A brassinosteroid signal regulated beta-tubulin GhTUB17 play a role in cotton fiber elongation by influencing microtubule organization

Abstract

Cotton (Gossypium hirsutum L.) is an important natural fiber crop in the world. Cotton fiber cell is an extremely elongated single cell and a major cash product of cotton plants. Both brassinosteroids (BRs) and cytoskeleton play essential roles in fiber cell elongation. However, the relationship of BRs with cytoskeleton in fiber elongation is largely unknown. In the study, a BRs responsive beta-tubulin gene GhTUB17 was identified, which preferentially expressed in fiber cell and peaked in the rapid elongation stage. GhTUB17 was up- and down-regulated by brassinolide (BL) and brassinozole (BRZ), respectively. Furthermore, compared with control, GhTUB17 expression was increased in transgenic fiber cell overexpressing GhBES1, a transcription factor in BRs signaling, while was decreased in the fiber of li-1, a short fiber mutant of upland cotton. GhBES1 could bind to the promoter of GhTUB17 and positively regulate its expression. Overexpressing GhTUB17 promoted fiber elongation while suppressing GhTUB17 inhibited fiber elongation. The arrangement patterns of both microtubule and microfilament were altered in transgenic cotton fibers. These results indicated that GhTUB17 was a target gene of GhBES1 and play an important role in fiber cell elongation by regulating the organization of microtubule and microfilament cytoskeleton. It provided a link between BRs and cytoskeleton in fiber cell elongation and a potential gene to improve the fiber quality, and shed light on understanding the action mechanism of BRs.