Biology subjects

Waszczak, C.

Publications and source records attributed to Waszczak, C..

4 recordsLinked to original sources

bioRxiv2025

The EGY1-SGR1 module controls chloroplast development and senescence by modulating photosynthetic functions

The chloroplast plays essential roles not only in production of biochemical energy and metabolism, but also in plant development, including senescence. We describe a mutant with an unusual progression of senescence and identify it as an allele of ethylene-dependent gravitropism-deficient and yellow-green 1 (egy1-5). EGY1 encodes a chloroplast-localized metalloprotease that regulates chlorophyll metabolism. The single egy1-5 mutant exhibits defects in various aspects of chloroplast function, including abnormal accumulation of photosynthetic complexes, defects in photosynthetic electron transfer chain and altered responses to the chemicals methyl viologen and lincomycin. Additionally, egy1 lacks guard cell chloroplasts. We performed a suppressor mutant screen in the egy1 background to identify new regulators of senescence and chloroplast development. We found two suppressors that restored green leaves and mapping revealed that both suppressors had mutations in STAY-GREEN 1 (SGR1). SGR1 encodes the Mg2+ dechelatase enzyme, which catalyses the first step in chlorophyll breakdown. Several defects in the egy1 mutant were either fully or partially suppressed in egy1 sgr1. This enabled the function of EGY1 to be isolated, independent of the pleiotropic effects of chlorophyll degradation. Our findings suggest that chlorophyll homeostasis regulates the overall development and function of the chloroplast as well as plant senescence. HighlightIdentifying new mutants with defects in chlorophyll metabolism and chloroplast development shows that proper chlorophyll homeostasis is necessary for maintaining functional chloroplasts.

plant biology↗

bioRxiv2020

Genetic screen to saturate guard cell signaling network reveals a role of GDP-L-fucose metabolism in stomatal closure

Guard cells regulate plant gas exchange by controlling the aperture of stomatal pores. The process of stomatal closure involves a multi-input signaling network that governs the activity of ion channels, which in turn regulate guard cell turgor pressure and volume. Here we describe a forward genetic screen to identify novel components involved in stomatal movements. Through an ozone-sensitivity approach combined with whole-rosette gas exchange analysis, 130 mutants of established stomatal regulators and 76 novel mutants impaired in stomatal closure were identified. One of the novel mutants was mapped to MURUS1 (MUR1), the first enzyme in de novo GDP-L-fucose biosynthesis. Defects in synthesis or import of GDP-L-Fuc into the Golgi apparatus resulted in impaired stomatal closure to multiple stimuli. Stomatal phenotypes observed in mur1 were independent from the canonical guard cell signaling and instead could be related to altered mechanical properties of guard cell walls. Impaired fucosylation of xyloglucan, N-linked glycans and arabinogalactan proteins did not explain the aberrant function of mur1 stomata, however our data suggest that the stomatal phenotypes observed in mur1 can at least partially be attributed to defective dimerization of rhamnogalactouronan-II. In addition to providing the genetic framework for future studies on guard cell signaling, our work emphasizes the impact of fucose metabolism on stomatal movement.

plant biology↗

bioRxiv2019

Dual-targeted transcription factors are required for optimal photosynthesis and stress responses in Arabidopsis thaliana

Chloroplast to nucleus retrograde signaling is essential for cell function, acclimation to fluctuating environmental conditions, plant growth and development. The vast majority of chloroplast proteins are nuclear-encoded and must be imported into the organelle after synthesis in the cytoplasm. This import is essential for the development of fully functional chloroplasts. On the other hand, functional chloroplasts act as sensors of environmental changes and can trigger acclimatory responses that influence nuclear gene expression. Signaling via mobile transcription factors (TFs) has been recently recognized as a way of communication between organelles and the nucleus. In this study, we performed a targeted reverse genetic screen to identify novel dual-localized TFs involved in chloroplast retrograde signaling during stress responses. We found that CHLOROPLAST IMPORT APPARATUS 2 (CIA2), a TF with putative plastid transit peptide can be detected in chloroplasts and the nucleus. Further, we found that CIA2, along with its homolog CIA2-like (CIL) act in an unequally redundant manner and are involved in the regulation of Arabidopsis responses to UV-AB, high light, and heat shock. Finally, our results suggest that both CIA2 and CIL are crucial for chloroplast translation. Our results contribute to a deeper understanding of signaling events in the chloroplast-nucleus cross-talk.\n\nSignificanceWe found that a transcription factor CIA2 can be located in chloroplasts and nucleus. CIA2 and is close homolog CIL are involved in protein translation and abiotic stress responses, and we suggest that they play an essential role in retrograde signaling between these organelles.

plant biology↗

bioRxiv2019

The role of strigolactones in regulation of stomatal conductance and plant-pathogen interactions in Arabidopsis thaliana

Strigolactones are a group of phytohormones that control shoot branching in Arabidopsis thaliana. However, in recent years they have been shown to affect many other plant processes. We previously showed that the strigolactone perception mutant more axillary branches 2 (max2) has increased susceptibility to plant pathogenic bacteria as a result of more open stomata as well as alterations in hormonal signalling. Here we show that both, strigolactone biosynthesis- (max3 and max4), and perception mutants (max2 and dwarf14) are significantly more sensitive to Pseudomonas syringae DC3000. Moreover, in response to P. syringae infection, high levels of SA accumulated in max2 and this mutant was ozone sensitive. To search for the mechanisms that could explain pathogen- and ozone sensitivity we performed gene expression analysis and several different assays that explore the function of guard cells and regulation of guard cell signalling.\n\nTreatments with GR24 (a strigolactone analogue) resulted in very modest changes in defence-related gene expression. In contrast, guard cell function was clearly impaired in max2 and depending on the assay used, also in max3, max4 and d14 mutants. Moreover, stomatal responses to stimuli that cause stomatal closure in wild-type plants (darkness, high CO2 and ABA) were analysed in the strigolactone mutants. In darkness both strigolactone biosynthesis and perception mutants showed reduced stomatal closure, whereas the response to high CO2 was impaired only in max2 and d14. The response to ABA was not impaired in any of the mutants. To position the role of MAX2 in the guard cell signalling network, max2 was crossed with mutants defective in ABA biosynthesis (aba2), in guard cell ABA signalling (ost1) and a scaffold protein required for proper ion channel activity (ghr1). The stomatal conductance of double mutants was consistently higher than the corresponding single mutants, suggesting that MAX2 acts in a signalling pathway that functions in parallel to the well characterized guard cell ABA signalling pathway. We propose that the impaired defence responses of max2 is related to more open stomata that allows increased entry of bacteria or air pollutants like ozone. Furthermore, as MAX2 appears to act in a specific branch of guard cell signalling (related to CO2 signalling), this protein could be one of the elusive components that allow guard cells to distinguish between different environmental conditions.

plant biology↗