Biology subjects

Harding, S. A.

Publications and source records attributed to Harding, S. A..

7 recordsLinked to original sources

bioRxiv2025

Loss of flavonol 3-O-glucosyltransferase activity confers soybean resistance to leaf-chewing insects

Caterpillars and beetles are among the most economically damaging defoliating insects, and their economic damage is predicted to increase in the coming decades. Hence the use of genetically derived resistance to supplement other pest control strategies is warranted. In soybean (Glycine max (L.) Merr.), a major determinant for resistance is the quantitative trait locus, QTL-M. Glyma07g14530, the gene underlying QTL-M, encodes a feeding-inducible flavonol 3-O-glycosyltransferase (F3GlcT or UGT78D2) that glucosylates kaempferol, as well as quercetin, myricetin, and isorhamnetin. The resistant allele has a premature stop codon in it, thus preventing the glucosylation and sequestration of flavonols in the vacuole, leading to a concomitant accumulation of proanthocyanidins and manifestation of resistance. Expressing the dominant (susceptible) allele in resistant plants restores susceptibility and silencing the susceptible allele results in resistance. The discovery and characterization of GmF3GlcT helps clarify the role of flavonoids in resistance to leaf-chewing insects and facilitates the development of insect-resistant cultivars that ultimately can lower production costs and reduce insecticide applications. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=131 SRC="FIGDIR/small/679769v1_ufig1.gif" ALT="Figure 1"> View larger version (46K): org.highwire.dtl.DTLVardef@10e2e77org.highwire.dtl.DTLVardef@ca905org.highwire.dtl.DTLVardef@12cb46corg.highwire.dtl.DTLVardef@1f9328b_HPS_FORMAT_FIGEXP M_FIG C_FIG The loss of flavonol 3-O-glucosyltransferase in soybean reduces feeding damage from defoliating insects and is accompanied by a concomitant increase in proanthocyanidins (red arrowhead). SignificanceUnraveling the biochemical and genetic basis of soybean resistance to leaf-chewing insects facilitates the development of new, naturally insect resistant varieties. Such varieties contribute to on-farm profitability and reduced concerns over pesticide residues in the field.

plant biology↗

bioRxiv2025

Leaf stage and roasting shape methylxanthine levels, chlorogenic acid, and overall metabolic profile of Ilex vomitoria leaf extracts

Yaupon holly (Ilex vomitoria) is a shrub native to the southeastern US whose leaves can be roasted and brewed into a caffeinated infusion. While production and consumption of yaupon tea is growing, not much is known about what influences downstream levels of caffeine and other metabolites within the leaf. To address this question, we used ultra-high performance liquid chromatography-mass spectrometry to measure the effect of leaf stage and roasting on the metabolome of yaupon leaves. We found caffeine levels strongly decreased with leaf stage but were not significantly affected by roasting. We also tentatively identified 100 chemicals that were dramatically increased by roasting, including several lactones and probable Maillard products related to known flavor compounds. These findings will help the yaupon tea industry produce a more consistent and tailored product, as well as lend insight into how leaf biochemistry changes over time.

biochemistry↗

bioRxiv2023

Sucrose or starch? The influence of tonoplast sucrose transporter perturbation on carbon partitioning for growth, defense, and winter protection in coppiced poplar

Non-structural carbohydrate reserves of stems and roots underpin overall tree fitness. These reserves also contribute to productivity under short-rotation management practices such as coppicing for bioenergy. While sucrose and starch comprise the predominant carbohydrate reserves of Populus, utilization is understood primarily in terms of starch turnover. The tonoplast sucrose transport protein SUT4 modulates sucrose export from source leaves to distant sinks during photoautotrophic growth, but the possibility of its involvement in remobilizing carbohydrates from sinks during heterotrophic growth has not been explored. Here, we used PtaSUT4-knockout mutants of Populus tremula x P. alba (INRA 717-1B4) in winter (cool) and summer (warm) glasshouse coppicing experiments to strain carbon demand and test for SUT4 involvement in reserve utilization. We show that epicormic bud emergence, subsequent growth, and xylem hexose increases were delayed or reduced in sut4 mutants following lower temperature winter coppicing. Depletion of stem reserves during post-coppice regrowth was not impaired in sut4, but sut4 winter maintenance costs may have been higher in metabolic terms. Bark accrual of abundant defense metabolites, including salicinoids, chlorogenic acids, and flavonoid products, was prioritized in the summer, but attenuated in sut4 mutants. Summer sprout growth was not reduced in sut4 compared to controls. Together, our results point to shifting priorities for SUT4 modulation of seasonal trade-offs between growth and other priorities in the stem and emerging buds during reserve utilization in Populus.

plant biology↗

bioRxiv2022

Shape analysis of Iron Age sheep astragali suggests west-to-east morphotype diffusion in the southern Levant

The movement of livestock across the Mediterranean is well-documented in the Neolithic era, but its significance during subsequent periods has received less attention. This study explores potential evidence for maritime connections between sheep populations in the Iron Age eastern Mediterranean by analyzing astragal bones from four coastal and inland sites in Israel and Cyprus. Employing an established geometric morphometric protocol, we investigated the hypothesis that intra-site morphological variability is higher in coastal sites, reflecting greater genetic diversity in the livestock populations. While our findings support this hypothesis, the conclusions are constrained by contextual and sample size limitations.

paleontology↗

bioRxiv2021

Multiplex knockout of trichome-regulating MYBs in poplar affects light sensitivity and triterpene accumulation

As the focus for CRISPR edited plants moves from proof-of-concept to real world applications, precise gene manipulation will increasingly require concurrent multiplex editing for polygenic traits. A common approach for editing across multiple sites is to design one gRNA per target; however, this complicates construct assembly and increases the possibility of off-target mutations. In this study, we utilized one gRNA to target MYB186, a known positive trichome regulator, as well as its paralogs MYB138 and MYB38 at a consensus site for mutagenesis in Populus tremula x P. alba INRA 717-1B4. Unexpected duplications of MYB186 and MYB138 resulted in a total of eight alleles for the three targeted genes in the hybrid poplar. Deep sequencing and PCR analyses confirmed editing across all eight targets in nearly all of the resultant glabrous mutants, ranging from small indels to large genomic dropouts, with no off-target activity detected at four potential sites. This highlights the effectiveness of a single gRNA targeting conserved exonic regions for multiplex editing. Additionally, cuticular wax and whole leaf analyses showed a complete absence of triterpenes in the trichomeless mutants, hinting at a previously undescribed role for the non-glandular trichomes of poplar. ONE SENTENCE SUMMARYTargeting conserved sequences with a single gRNA allowed efficient mutagenesis of a multigene family and the recovery of trichomeless and triterpene-free poplar mutants.

plant biology↗

bioRxiv2020

Defoliation-induced compensatory transpiration is compromised in SUT4-RNAi Populus

Leaf sucrose contents are high in species of the genus Populus and other temperate tree taxa. Sucrose is subcellularly compartmentalized, but assumptions about the physiological relevance of such partitioning remain largely unexplored. In this study, the effects of partial defoliation treatments on water uptake, leaf gas exchange properties, non-structural carbohydrate abundance in source and sink organs, and growth were compared in poplars with normal or impaired intracellular sucrose trafficking. The tonoplast sucrose transporter PtaSUT4 is well expressed in leaves of P. tremula x P. alba (INRA 717-IB4), and its inhibition by RNA-interference (RNAi) is known to affect leaf sucrose abundance. After partial defoliation, maximum photosynthesis rates increased while intercellular CO2 decreased with trajectories that were similar in wild type and SUT4-RNAi lines. Leaf transpiration increased more robustly in wild-type than RNAi plants, while leaf water content increased more in RNAi lines. Stomatal conductance did not differ between genotypes, nor did it increase with defoliation. Post-defoliation reductions in steady-state levels of sucrose, the major hexoses (glucose and fructose) and starch were similar in wild-type and SUT4-RNAi shoot sinks. Water uptake and stem growth after partial defoliation were not as well sustained in RNAi as in wild-type plants. The data suggest that vacuolar efflux of sucrose by PtaSUT4 more clearly facilitated adjustments in water uptake than sucrose export following leaf removal.

plant biology↗

bioRxiv2019

Compensatory guaiacyl lignin biosynthesis at the expense of syringyl lignin in 4CL1-knockout poplar

The lignin biosynthetic pathway is highly conserved in angiosperms, yet pathway manipulations give rise to a variety of taxon-specific outcomes. Knockout of lignin-associated 4-coumarate:CoA ligases (4CLs) in herbaceous species mainly reduces guaiacyl (G) lignin and enhances cell wall saccharification. Here we show that CRISPR-knockout of 4CL1 in Populus tremula x alba preferentially reduced syringyl (S) lignin, with negligible effects on biomass recalcitrance. Concordant with reduced S-lignin was downregulation of ferulate 5-hydroxylases (F5Hs). Lignification was largely sustained by 4CL5, a low-affinity paralog of 4CL1 typically with only minor xylem expression or activity. Levels of caffeate, the preferred substrate of 4CL5, increased in line with significant upregulation of caffeoyl shikimate esterase1. Upregulation of caffeoyl-CoA O-methyltransferase1 and downregulation of F5Hs are consistent with preferential funneling of 4CL5 products toward G-lignin biosynthesis at the expense of S-lignin. Thus, transcriptional and metabolic adaptations to 4CL1-knockout appear to have enabled 4CL5 catalysis at a level sufficient to sustain lignification. Finally, genes involved in sulfur assimilation, the glutathione-ascorbate cycle and various antioxidant systems were upregulated in the mutants, suggesting cascading responses to perturbed thioesterification in lignin biosynthesis. One sentence summaryKnockout of lignin-associated 4CL1 in Populus reveals a 4CL5-dependent, caffeate-modulated compensatory pathway for lignification with links to thiol redox balance and sulfur assimilation.

plant biology↗