Biology subjects

Harding, S. A.

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

2 recordsLinked to original sources

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↗