Plant Biology
Raffinose synthase enhances drought tolerance through raffinose synthesis or galactinol hydrolysis in maize and Arabidopsis plants
Raffinose and its precursor galactinol accumulate in plant leaves during abiotic stress. RAFFINOSE SYNTHASE (RAFS) catalyzes raffinose formation by transferring a galactosyl group of galactinol to sucrose. However, whether RAFS contributes to plant drought tolerance and, if so, by what mechanism remains unclear. In this study, we report that expression of RAFS from maize (or corn, Zea mays) (ZmRAFS) is induced by drought, heat, cold, and salinity stresses. We found that zmrafs mutant maize plants completely lack raffinose and hyper-accumulate galactinol and are more sensitive to drought stress than the corresponding null-segregant (NS) plants.Proteomic analysis reveals that sugar and fatty acid metabolisms play a central role in sterility of the male-sterile line 1355A of cotton
Cotton (Gossypium spp.) is one of the most important economic crops and exhibits yield-improving heterosis in specific hybrid combinations. The genic male-sterility system is the main strategy used for producing heterosis in cotton. To better understand the mechanisms of male sterility in cotton, we carried out two-dimensional electrophoresis (2-DE) and label-free quantitative proteomics analysis in the anthers of two near-isogenic lines, the male-sterile line 1355A and the male-fertile line 1355B.Identification of the Plant Ribokinase and Discovery of a Role for Arabidopsis Ribokinase in Nucleoside Metabolism
Ribose can be used for energy or as a component of several important biomolecules, but for it to be used in either capacity it must first be phosphorylated by ribokinase (RBSK). RBSK proteins are part of the phosphofructokinase-B (pfkB) family of carbohydrate kinases. Sequence comparisons of pfkB proteins from the model plant Arabidopsis thaliana with the human and Escherichia coli RBSK identified a single candidate RBSK, At1g17160 (AtRBSK). AtRBSK is more similar to predicted RBSKs from other plant species and known mammalian and prokaryotic RBSK than to all other PfkB proteins in Arabidopsis.Degradation of Glucan Primers in the Absence of Starch Synthase 4 Disrupts Starch Granule Initiation in Arabidopsis
Arabidopsis leaf chloroplasts typically contain five to seven semicrystalline starch granules. It is not understood how the synthesis of each granule is initiated or how starch granule number is determined within each chloroplast. An Arabidopsis mutant lacking the glucosyl-transferase, STARCH SYNTHASE 4 (SS4) is impaired in its ability to initiate starch granules; its chloroplasts rarely contain more than one large granule, and the plants have a pale appearance and reduced growth. Here we report that the chloroplastic α-amylase AMY3, a starch-degrading enzyme, interferes with granule initiation in the ss4 mutant background.Structural Dissection of the Maltodextrin Disproportionation Cycle of the Arabidopsis Plastidial Disproportionating Enzyme 1 (DPE1)
Background: Arabidopsis maltodextrin disproportionating enzyme 1 (AtDPE1) plays a key role in chloroplast starch degradation.Results: Six AtDPE1 structures define the active site and reveal mechanistically relevant conformations of both the enzyme and substrate.Conclusion: Substrates are captured through loop rearrangements; the subtle deployment of active site residues controls catalysis.Significance: A molecular level understanding of the complete disproportionation cycle of AtDPE1 is presented.
