Cotton beta-glucosidase gene GhBG1A coordinates fiber transition from elongation to secondary cell wall deposition

Abstract：Cotton fiber is the most important natural textile raw material in the world. It also represents an outstanding single-celled model for understanding plant cell elongation and cell wall and cellulose biosynthesis. Compared to extensive studies on fiber initiation and elongation processes, much less is known about the molecular basis underlying secondary cell wall cellulose deposition, a process profoundly impacting mature fiber properties. In this study, we identified a gene, GhBG1A, encoding glycosyl hydrolase family 3 beta-glucosidase, which coordinates cotton fiber elongation and cellulose deposition through regulating sugar metabolism. GhBG1A was preferentially expressed in cotton fibers and significantly associated with fiber length and strength. Overexpression of GhBG1A at fiber elongation stage significantly reduced fiber length, but remarkably increased cellulose biosynthesis leading to thicker fiber cell wall. Molecular and biochemical studies indicate that sucrose content and expression levels of cellulose biosynthesis related genes was evidently increased in transgenic cotton fibers. Moreover, using two cultivated tetraploid cotton species with distinctly different fiber qualities, higher transcript levels and enzyme activities of GhBG1A homologs were detected at fiber secondary cell wall (SCW) deposition stage in G. barbadense cv. H7124, which possesses elite fibers, than that in G. hirsutum acc. TM-1. Taken together, GhBG1A plays an important role in fiber transition from elongation to SCW deposition, and fine-tune overexpression of GhBG1A homolog at fiber SCW stage could improve fiber qualities in cotton fiber quality breeding program.