Suppression of GhGLU19 encoding β-1,3-glucanase promotes seed germination in cotton

The GARP family transcription factor MtHHO3 negatively regulates salt tolerance in Medicago truncatula

High salinity is one of the detrimental environmental factors restricting plant growth and crop production throughout the world. This study demonstrated that the GARP family transcription factor MtHHO3 is involved in response to salt stress and abscisic acid (ABA) signaling in Medicago truncatula. The transcription of MtHHO3 was repressed by salt, osmotic stress, and ABA treatment. The seed germination assay showed that, overexpression of MtHHO3 in Arabidopsis thaliana caused hypersensitivity to salt and osmotic stress, but increased resistance to ABA inhibition. Overexpression of MtHHO3 in M. truncatula resulted in decreased tolerance of salinity, while loss-of-function mutants mthho3-1 and mthho3-2 were more resistant to salt stress compared with wild-type plants. qRT-PCR analyses showed that MtHHO3 downregulated the expression of genes in stress and ABA responsive pathways. We further demonstrated that MtHHO3 repressed the transcription of the pathogenesis-related gene MtPR2 by binding to its promoter. Overall, these results indicate that MtHHO3 negatively regulates salt stress response in plants and deepen our understanding of the role of the GARP subfamily transcription factors in modulating salt stress and ABA signaling.

A cell wall-localized β-1,3-glucanase promotes fiber cell elongation and secondary cell wall deposition

β-1,3-glucanase functions in plant physiological and developmental processes. However, how β-1,3-glucanase participates in cell wall development remains largely unknown. Here, we answered this question by examining the role of GhGLU18, a β-1,3-glucanase, in cotton (Gossypium hirsutum) fibers, in which the content of β-1,3-glucan changes dynamically from 10% of the cell wall mass at the onset of secondary wall deposition to <1% at maturation. GhGLU18 was specifically expressed in cotton fiber with higher expression in late fiber elongation and secondary cell wall (SCW) synthesis stages. GhGLU18 largely localized to the cell wall and was able to hydrolyze β-1,3-glucan in vitro. Overexpression of GhGLU18 promoted polysaccharide accumulation, cell wall reconstruction, and cellulose synthesis, which led to increased fiber length and strength with thicker cell walls and shorter pitch of the fiber helix. However, GhGLU18-suppressed cotton resulted in opposite phenotypes. Additionally, GhGLU18 was directly activated by GhFSN1 (fiber SCW-related NAC1), a NAC transcription factor reported previously as the master regulator in SCW formation during fiber development. Our results demonstrate that cell wall-localized GhGLU18 promotes fiber elongation and SCW thickening by degrading callose and enhancing polysaccharide metabolism and cell wall synthesis.