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Results for “Plant Biology”

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bioRxiv2018

Effect of Thiobacillus and superabsorbent on essential oil components in Thyme species

Optimal nutrition along with non-stress conditions has a significant impact on the quantity and quality of essential oil in medicinal plants. The objective of this research was to examine the possibility of improving the quantity and quality of essential oil in thyme through nutrition of the seedlings using Thiobacillus bio-fertilizer and treatment by Superabsorbent. For this purpose, seedlings of two thyme species (Thymus vulgaris and Thymus daenensis) were sown in pots and exposed to different levels of Thiobacillus and superabsorbent. Results of Gas Chromatography Mass Spectrometry (GC/MS) revealed that the main compounds detected for T. vulgaris were thymol (31.5%), p-cymene (23.4%),{gamma} -terpinene (13.9%), linalool (38.3%) and carvacrol (2.7%) while the main compounds of T. daenensis were thymol (51.2%), o-cymene (12.9%),{gamma} -terpinene (4.5%), linalool (1.7%) and borneol (3.1%). Furthermore, the application of Thiobacillus had a significant effect on -pinene content (p = 0.05). Moreover, the interaction between superabsorbent and Thiobacillus significantly changed the percentage of thymol, borneol, and caryophyllene. In conclusion, the mean of essence components in T. vulgaris was more than T. daenensis with the exception of thymol and caryophyllene.

plant biology↗

bioRxiv2018

Altered Gene Regulatory Networks are Associated with the Transition from C3 to Crassulacean Acid Metabolism in Erycina (Oncidiinae: Orchidaceae)

Crassulacean acid metabolism (CAM) photosynthesis is a modification of the core C3 photosynthetic pathway that improves the ability of plants to assimilate carbon in water-limited environments. CAM plants fix CO2 mostly at night, when transpiration rates are low. All of the CAM pathway genes exist in ancestral C3 species, but the timing and magnitude of expression are greatly altered between C3 and CAM species. Understanding these regulatory changes is key to elucidating the mechanism by which CAM evolved from C3. Here we use two closely related species in the Orchidaceae, Erycina pusilla (CAM) and Erycina crista-galli (C3), to conduct comparative transcriptomic analyses across multiple time points. Clustering of genes with expression variation across the diel cycle revealed some canonical CAM pathway genes similarly expressed in both species, regardless of photosynthetic pathway. However, gene network construction indicated that 149 gene families had significant differences in network connectivity and were further explored for these functional enrichments. Genes involved in light sensing and ABA signaling were some of the most differently connected genes between the C3 and CAM Erycina species, in agreement with the contrasting diel patterns of stomatal conductance in C3 and CAM plants. Our results suggest changes to transcriptional cascades are important for the transition from C3 to CAM photosynthesis in Erycina.

plant biology↗

bioRxiv2018

pH gradient mitigation in the leaf cell secretory pathway alters the defense response of Nicotiana benthamiana to agroinfiltration

Partial neutralization of the Golgi lumen pH by ectopic expression of influenza virus M2 proton channel stabilizes acid-labile and protease-susceptible recombinant proteins in the plant cell secretory pathway. Here, we assessed the impact of M2 channel expression on the proteome of Nicotiana benthamiana leaf tissue infiltrated with the bacterial gene vector Agrobacterium tumefaciens, keeping in mind the key role of pH homeostasis on secreted protein processing and the involvement of protein secretion processes in plant cells upon microbial challenge. The proteomes of leaves agroinfiltrated with an empty vector or with an M2 channel-encoding vector were compared with the proteome of non-infiltrated leaves using a iTRAQ quantitative proteomics procedure. Leaves infiltrated with the empty vector had a low soluble protein content compared to non-infiltrated leaves, associated with a strong decrease of photosynthesis-associated proteins (including Rubisco) and a parallel increase of stress-related secreted proteins (including pathogenesis-related proteins, protease inhibitors and molecular chaperones). M2 expression partly compromised these alterations of the proteome to restore original soluble protein and Rubisco contents, associated with higher levels of translation-associated (ribosomal) proteins and reduced levels of stress-related proteins in the apoplast. Proteome changes in M2-expressing leaves were determined both transcriptionally and post-transcriptionally, to alter the steady-state levels of proteins not only along the secretory pathway but also in other cellular compartments including the chloroplast, the cytoplasm, the nucleus and the mitochondrion. These data illustrate the cell-wide influence of Golgi lumen pH homeostasis on the leaf proteome of N. benthamiana plants responding to microbial challenge. They underline in practice the relevance of carefully considering the eventual off-target effects of accessory proteins used to modulate specific cellular or metabolic functions in plant protein biofactories.

plant biology↗

bioRxiv2018

Classifying cold stress responses of inbred maize seedlings using RGB imaging

Increasing the tolerance of maize seedlings to low temperature episodes could mitigate the effects of increasing climate variability on yield. To aid progress toward this goal, we established a growth chamber-based system for subjecting seedlings of 40 maize inbred genotypes to a defined, temporary cold stress while collecting digital profile images over a 9-day time course. Image analysis performed with PlantCV software quantified shoot height, shoot area, 14 other morphological traits, and necrosis identified by color analysis. Hierarchical clustering of changes in growth rates of morphological traits and quantification of leaf necrosis over two time intervals resulted in three clusters of genotypes, which are characterized by unique responses to cold stress. For any given genotype, the set of traits with similar growth rates is unique. However, the patterns among traits are different between genotypes. Cold sensitivity was not correlated with the latitude where the inbred varieties were released suggesting potential further improvement for this trait. This work will serve as the basis for future experiments investigating the genetic basis of recovery to cold stress in maize seedlings.

plant biology↗

bioRxiv2018

Nitrate inhibition of nodule formation in Medicago truncatula is mediated by ACC SYNTHASE 10

Legumes form a mutualistic endosymbiosis with nitrogen-fixing rhizobia. These rhizobia are housed intracellularly in specialised lateral root organs, called nodules. Initiation of these nodules is triggered by bacterial derived signalling molecules, lipochitooligosaccharides (LCO). The process of nitrogen fixation is highly energy-demanding and therefore nodule initiation is tightly regulated. Nitrate is a potent inhibitor of nodulation. However, the precise mechanisms by which nitrate inhibits nodulation is poorly understood. Here, we demonstrate that in Medicago truncatula nitrate interferes with the transcriptional regulation of the ethylene biosynthesis gene ACC SYNTHASE 10. ACSs commit the rate limiting step in ethylene biosynthesis and in M. truncatula ACS10 is highly expressed in the zone of the root where nodulation occurs. Our results show that a reduction in ACS10 expression in response to LCO exposure correlates with the ability to form nodules. In addition, RNAi-mediated knockdown of ACS10 confers nodulation ability under otherwise inhibitory nitrate conditions. This discovery sheds new light on how ethylene is involved in the inhibition of nodulation by nitrate, bringing us one step closer to understanding how plants regulate their susceptibility towards rhizobia.

plant biology↗

bioRxiv2018

Triose phosphate utilization and beyond: from photosynthesis to end-product synthesis

During photosynthesis plants fix CO2 from the atmosphere onto ribulose-bisphosphate producing 3-phosphoglycerate, which is reduced to triose phosphates (TPs). The TPs are then converted into the end products of photosynthesis. When a plant is photosynthesizing very quickly it may not be possible to commit photosynthate to end product as fast as it is produced, causing a decrease in available phosphate and limiting the rate of photosynthesis to the rate of triose phosphate utilization (TPU). The occurrence of an observable TPU limitation is highly variable based on species and especially growth conditions, with TPU capacity seemingly regulated to be in just slight excess of the likely photosynthetic rate. The physiological effects of TPU limitation are discussed with an emphasis on interactions between the Calvin-Benson cycle and the light reactions. Methods for detecting TPU-limited data from gas exchange data are detailed, and the impact on modeling of some physiological effects are shown. Special consideration is given to common misconceptions about TPU.\n\nHighlightPhotosynthetic triose phosphate utilization limitation is discussed, highlighting misleading points in physiology and focusing on regulation.

plant biology↗

bioRxiv2018

Unleashing floret fertility by a mutated homeobox gene improved grain yield during wheat evolution under domestication

Floret fertility is a key trait to determine the number of grains per inflorescence in cereals. During wheat (Triticum sp.) evolution, floret fertility has been increased and current bread wheat (T. aestivum L.) produces three to five grains per spikelet; however, little is known about the genetic basis controlling floret fertility. Here we identify the quantitative trait locus Grain Number Increase 1 (GNI1), encoding a homeodomain leucine zipper class I (HD-Zip I) transcription factor. GNI1 evolved in the Triticeae through gene duplication and functionalization. GNI1 was predominantly expressed in the most apical floret primordia and parts of the rachilla, suggesting that GNI1 inhibits rachilla growth and development. GNI1 expression decreased during wheat evolution, and as a consequence, more fertile florets and grains per spikelet are being produced. Genetic analysis revealed that the reduced-function allele of GNI1-A contributes to increase the number of fertile florets per spikelet. The knockdown of GNI1 in transgenic hexaploid wheat improved fertile floret and grain number. Furthermore, wheat plants carrying the impaired allele increased grain yield under field conditions. Our findings illuminate that gene duplication and functionalization generated evolutionary novelty for floret fertility (i.e. reducing floral numbers) while the mutations towards increased grain production were under selection during wheat evolution under domestication.\n\nSignificance StatementGrain number is a fundamental trait for cereal grain yield; but its underlying genetic basis is mainly unknown in wheat. Here we show for the first time a direct link between increased floret fertility, higher grain number per spike and higher plot-yields of wheat in the field. We have identified GNI1 gene encoding an HD-Zip I transcription factor responsible for increased floret fertility. The wild type allele imposes an inhibitory role specifically during rachilla development, indicating that expression of this protein actively shuts-down grain yield potential; whereas, the reduced-function allele enables more florets and grains to be produced. GNI1 evolved through gene duplication in Triticeae and its mutations were under parallel human selection during wheat and barley evolution under domestication.

plant biology↗

bioRxiv2018

Defining the developmental program leading to meiosis in maize

In multicellular organisms, the entry into meiosis is a complex process characterized by increasing levels of meiotic specialization. We used single-cell RNA-sequencing to reconstruct the developmental program into meiosis in maize. We observed a smooth continuum of expression stages leading up to meiosis, followed by a sharp reorganization of the transcriptome in early meiotic prophase. This latter transcriptional shift was dramatic, with 26.7% of expressed genes changing by 2 fold or more, and occurred just prior to a proposed cell cycle checkpoint. Changes in cell physiology accompanied the nuclear events of meiosis, including a decrease in protein translation capacity and increase in membrane-bound organelles. We further identified differences in gene expression between the mitotic and meiotic cell cycles. Our results uncover a multi-step pathway into meiosis and highlight the power of single cell RNA-seq to define developmental transitions.

plant biology↗

bioRxiv2018

Root endophytes improve physiological performance and yield in crops under salt stress by up-regulating the foliar sodium concentration

Increase in the soil salinity will be a conspicuous constraint for both native plant communities as well as several crops worldwide. In this context plant root-associated fungi appear as a new strategy to improve ecophysiological performance and yield of crops under abiotic stress. Here, we evaluated how the inoculation of fungal endophytes isolated from Antarctic plants can improve the ecophysiological performance in cultivars of tomato and lettuce, grown under different salt conditions. In addition, we assessed if the expression of the NHX1 gene that is related with salt tolerance is enhanced in presence of fungal endophytes. Finally, we evaluated the regulation the nutritional status and specifically the Na+ content in leaves. Overall, those individuals with presence of endophytes showed higher ecophysiological performance. In addition, the presence of fungal endophytes was correlated with a higher regulation of ion homeostasis by enhanced expression of NHX1 gene. Our results suggest that presence of fungal endophytes could minimize the negative effect of salt by improving osmotic tolerance through ecophysiological and molecular mechanisms. Thus, root-endophytes might be a successful biotechnological tool to maintain high levels of ecophysiological performance and productivity in zones under osmotic stress, acting as potential solution to maintain the global food security.\n\nHighlightWe showed that functional symbiosis improve the physiological performance and yield in crops subjected to salinity, by biochemical and molecular mechanisms. Thus, here we pointed a successful strategy to meet the future challenges for help to maintain the food security.

plant biology↗

bioRxiv2018

Multi-lab EcoFAB study shows highly reproducible physiology and depletion of soil metabolites by a model grass

O_LIThere is a dynamic reciprocity between plants and their environment: On one hand, the physiochemical properties of soil influence plant morphology and metabolism, while on the other, root morphology and exudates shape the environment surrounding roots. Here, we investigate both of these aspects as well as the reproducibility of these responses across laboratories.\nC_LIO_LIThe model grass Brachypodium distachyon was grown in phosphate-sufficient and phosphate-deficient mineral media, as well as in sterile soil extract, within fabricated ecosystem (EcoFAB) devices across four laboratories.\nC_LIO_LITissue weight and phosphate content, total root length, root tissue and exudate metabolic profiles were found to be consistent across laboratories and distinct between experimental treatments. Plants grown in soil extract were morphologically and metabolically distinct in all laboratories, with root hairs four times longer compared to other growth conditions. Further, plants depleted half of the investigated metabolites from the soil extract.\nC_LIO_LITo interact with their environment, plants not only adapt morphology and release complex metabolite mixtures; they also selectively deplete a range of soil-derived metabolites. The EcoFABs utilized here generated high inter-laboratory reproducibility, demonstrating that their value in standardized investigations of plant traits.\nC_LI

plant biology↗

bioRxiv2018

Gibberellin response in the embryo epidermis regulates germination uniformity in response to seed priming

Uniformity in seed germination remains a primary objective in plant-based food production systems, ensuring predictable and synchronized harvest dates, while suppressing weeds. Treatments including priming can be used to increase germination uniformity and increase the value of commercial seeds. Despite the economic and agronomic importance of seed enhancement treatments, little is known as to how they work at a mechanistic level. Using a combination of molecular genetics and microscopy, we established that hydropriming limits embryo growth genetic programs at an early stage of germination. Conversely, gibberellin (GA) and abscisic acid (ABA)-associated molecular processes progress to later stages of this developmental chronology. The response to GA was specifically affected in the epidermis of germinating embryos in response to hydropriming based on reporter gene expression. The reduction of GA response specifically in the embryo epidermis resulted in increased uniformity of seed germination following hydropriming relative to control seeds. This represents the identification of both a molecular signalling pathway and cell type that are acting to enhance the agronomic germination properties of seed populations. This provides molecular and cellular targets which may be genetically manipulated to enhance seed germination and food production in agronomic species.

plant biology↗

bioRxiv2018

Methyl viologen can affect mitochondrial function in Arabidopsis.

Reactive oxygen species (ROS) are key signalling intermediates in plant metabolism, defence, and stress adaptation. The chloroplast and mitochondria are centres of metabolic control and ROS production, which coordinate stress responses in other cell compartments. The herbicide and experimental tool, methyl viologen (MV) induces ROS generation in the chloroplast under illumination, but is also toxic in non-photosynthetic organisms. We used MV to probe plant ROS signalling in compartments other than the chloroplast. Taking a genetic approach in Arabidopsis thaliana, we used natural variation, QTL mapping, and mutant studies with MV in the light, but also under dark conditions, when the chloroplast electron transport is inactive. These studies revealed a light-independent MV-induced ROS-signalling pathway, suggesting mitochondrial involvement. Mitochondrial Mn SUPEROXIDE DISMUTASE was required for ROS-tolerance and the effect of MV was enhanced by exogenous sugar, providing further evidence for the role of mitochondria. Mutant and hormone feeding assays revealed roles for stress hormones in organellar ROS-responses. The radical-induced cell death1 mutant, which is tolerant to MV-induced ROS and exhibits altered mitochondrial signalling, was used to probe interactions between organelles. Our studies implicate mitochondria in the response to ROS induced by MV.

plant biology↗

bioRxiv2018

Tomato fruit ripening factor NOR controls leaf senescence

NAC transcription factors (TFs) are important regulators of expressional reprogramming during plant development, stress responses and leaf senescence. NAC TFs also play important roles in fruit ripening. In tomato (Solanum lycopersicum), one of the best characterized NAC involved in fruit ripening is NON-RIPENING (NOR) and the non-ripening (nor) mutation has been widely used to extend fruit shelf life in elite varieties. Here, we show that NOR additionally controls leaf senescence. Expression of NOR increases with leaf age, and developmental as well as dark-induced senescence are delayed in the nor mutant, while overexpression of NOR promotes leaf senescence. Genes associated with chlorophyll degradation as well as senescence-associated genes (SAGs) show reduced and elevated expression, respectively, in nor mutants and NOR overexpressors. Overexpression of NOR also stimulates leaf senescence in Arabidopsis thaliana. In tomato, NOR supports senescence by directly and positively regulating the expression of several senescence-associated genes including, besides others, SlSAG15 and SlSAG113, SlSGR1 and SlYLS4. Finally, we find that another senescence control NAC TF, namely SlNAP2, acts upstream of NOR to regulate its expression. Our data support a model whereby NAC TFs have often been recruited by higher plants for both, the control of leaf senescence and fruit ripening.

plant biology↗

bioRxiv2018

A histidine kinase gene is required for large radius root tip circumnutation and surface exploration in rice

The intricate growth patterns that accompany plant organ elongation have long intrigued biologists 1. Circumnutation refers to the circular or elliptical growth of the tip of a plant organ around a central axis. While the utility of circumnutation for climbing plants is clear, its function in roots is less obvious. Additionally, the genetic requirements for root circumnutation are not known. Here we show that mutations in a gene encoding a histidine kinase abolish large radius root tip circumnutation in rice. Using a gel-based imaging system and a whole genome sequenced mutant population, we identified three different mutant alleles of the gene OsHK1 that exhibit increased seedling root depth. Time-lapse imaging indicated that this phenotype is likely due to a lack of large radius root tip circumnutation in OsHK1 mutants. Treatment of mutant roots with the plant hormone zeatin rescues circumnutation, indicating that OsHK1 functions in a cytokinin-related signaling pathway. We found that OsHK1 mutants are impaired in their ability to explore flat surfaces, suggesting that circumnutation facilitates root exploration at the interface of compacted soil horizons.

plant biology↗

bioRxiv2018

FT/FD-GRF5 repression loop directs growth to increase soybean yield

Major advances in crop yield are eternally needed to cope with population growth. To balance vegetative and reproductive growth plays an important role in agricultural yield. To extend vegetative phase can increase crop yield, however, this strategy risks loss of yield in the field as crops may not mature in time before winter come. Here, we identified a repression feedback loop between GmFTL/GmFDL and GmGRF5-1 (Glycine-max-Flowering-Locus-T/Glycine-max-FDL and Glycine-max-GROWTH-REGULATING-FACTOR5-1), which functions as a pivotal regulator in balancing vegetative and reproductive phases in soybean. GmFTL/GmFDL and GmGRF5-1 directly repress gene expression each other. Additionally, GmGRF5-1 enhances vegetative growth by directly enhancing expression of photosynthesis- and auxin synthesis-related genes. To modulate the loop, such as fine-tuning GmFTL expression to trade-off vegetative and reproductive growth, increases substantially soybean yield in the field. Our findings not only uncover the mechanism balancing vegetative and reproductive growth, but open a new window to improve crop yield.

plant biology↗

bioRxiv2018

Thermal acclimation of photosynthetic activity and Rubisco content in two hybrid poplar clones

The mechanistic bases of thermal acclimation of net photosynthetic rate (An) are still difficult to discern and empirical research remains limited, particularly for hybrid poplar. In the present study, we examined the contribution of a number of biochemical and biophysical traits on thermal acclimation of An for two hybrid poplar clones. We grew cuttings of Populus maximowiczii x Populus nigra (MxN) and Populus maximowiczii x Populus balsamifera (MxB) clones under two day/night temperature of 23{degrees}C/18{degrees}C and 33{degrees}C /27{degrees}C and under low and high soil nitrogen level. After 10 weeks, we measured leaf RuBisCO and RuBisCO activase (RCA) amounts and the temperature response of An, dark respiration (Rd), stomatal conductance, (gs), maximum carboxylation rate of CO2 (Vcmax) and photosynthetic electron transport rate (J). Results showed that a 10{degrees}C increase in growth temperature resulted in a shift in thermal optimum (Topt) of An of 6.2{+/-}1.6 {degrees}C and 8.0{+/-}1.2 {degrees}C for clone MxB and MxN respectively, and an increased An and gs at the growth temperature for clone MxB but not MxN. RuBisCO amount was increased by N level but was insensitive to growth temperature while RCA amount and the ratio of its short to long isoform was stimulated by warm condition for clone MxN and at low N for clone MxB. The activation energy of Vcmax and J decreased under warm condition for clone MxB and remain unchanged for clone MxN. Our study demonstrated the involvement of both RCA, activation energy of Vcmax and stomatal conductance in thermal acclimation of An.

plant biology↗

bioRxiv2018

Heterotrimeric G-proteins in unfolded protein response mediate plant growth-defense tradeoffs upstream of steroid and immune signaling

FLAGELLIN-SENSITIVE 2 (FLS2) is a plant immune receptor that binds bacterial flagellin to activate immune signaling. This immune signal is transduced by a heterotrimeric G protein complex at the plasma membrane and activates downstream signaling. However, it is unknown whether the heterotrimeric G proteins have functions at other subcellular locations away from the plasma membrane. Here, we show that components of the heterotrimeric G protein complex stabilize FLS2 protein levels by inhibiting the autophagic degradation of FLS2. Using genetic analysis, we determined that mutations of G protein components resulted in reduced immune signaling in part due to decreased FLS2 protein levels. Furthermore, reduction of FLS2 protein levels was caused by elevated proteasomal and autophagic degradation of FLS2. Genetic inhibition of autophagy in G protein mutants rescued FLS2 levels and immunity. Our findings suggest that the heterotrimeric G protein components, in addition to being part of the heterotrimeric G protein complex that transduces signals at the plasma membrane, also function away from the plasma membrane to control FLS2 protein levels. These results expand the functional capacity of the heterotrimeric G protein complexes in plant immunity.

plant biology↗

bioRxiv2018

SmbHLH37 functions antagonistically with SmMYC2 in regulating jasmonate-mediated biosynthesis of phenolic acids in Salvia miltiorrhiza

Jasmonates (JAs) are integral to various defense responses and induce biosynthesis of many secondary metabolites. MYC2, a basic helix-loop-helix (bHLH) transcription factor (TF), acts as a transcriptional activator of JA signaling. MYC2 is repressed by the JASMONATE ZIM-domain (JAZ) proteins in the absence of JA, but de-repressed by the protein complex SCFCOI1 on perception of JA. We previously reported that overexpression of SmMYC2 promotes the production of salvianolic acid B (Sal B) in Salvia miltiorrhiza. However, the responsible molecular mechanism is unclear. Here, we showed that SmMYC2 binds to and activates the promoters of its target genes SmTAT1, SmPAL1, and SmCYP98A14 to activate Sal B accumulations. SmbHLH37, a novel bHLH gene significantly up-regulated by constitutive expression of SmMYC2, was isolated from S. miltiorrhiza for detailed functional characterization. SmbHLH37 forms a homodimer and interacts with SmJAZ3/8. Overexpression of SmbHLH37 substantially decreased yields of Sal B. SmbHLH37 binds to the promoters of its target genes SmTAT1 and SmPAL1 and blocks their expression to suppress the pathway for Sal B biosynthesis. These results indicate that SmbHLH37 negatively regulates JA signaling and functions antagonistically with SmMYC2 in regulating Sal B biosynthesis in S. miltiorrhiza.

plant biology↗