Biology subjects

Nyamdari, B.

Publications and source records attributed to Nyamdari, B..

3 recordsLinked to original sources

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↗

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↗

bioRxiv2018

A role for phylloquinone biosynthesis in the plasma membrane as revealed in a non-photosynthetic parasitic plant

Phylloquinone is a lipophilic naphthoquinone found predominantly in chloroplasts and best known for its function in photosystem I electron transport and disulfide bridge formation of photosystem II subunits. Phylloquinone has also been detected in plasma membrane preparations of heterotrophic tissues with potential transmembrane redox function, but the molecular basis for this noncanonical pathway is unknown. Here we provide evidence of plasma membrane phylloquinone biosynthesis in a nonphotosynthetic holoparasite Phelipanche aegyptiaca. A nonphotosynthetic and nonplastidial role for phylloquinone is supported by transcription of phylloquinone biosynthetic genes during seed germination and haustorium development, by plasma membrane-localization of alternative terminal enzymes, and by detection of phylloquinone in germinated seeds. Comparative gene network analysis with photosynthetically competent parasites revealed a bias of Phelipanche phylloquinone genes toward coexpression with oxidoreductases involved in plasma membrane electron transport. Genes encoding the plasma membrane phylloquinone pathway are also present in several photoautotrophic taxa of Asterids, suggesting an ancient origin of multifunctionality. Our findings suggest that nonphotosynthetic holoparasites exploit alternative targeting of phylloquinone for transmembrane redox signaling associated with parasitism.

plant biology↗