Pectate lyase-like Gene GhPEL76 regulates organ elongation in Arabidopsis and fiber elongation in cotton

Pectate lyases (PELs) play important roles in plant growth and development, mainly by degrading the pectin in primary cell walls. However, the role of PELs in cotton fiber elongation, which also involves changes in cellular structure and components, is poorly understood. Therefore, we aimed to isolate and characterize GhPEL76, as we suspected it to contribute to the regulation of fiber elongation. Expression analysis (qRT-PCR) revealed that GhPEL76 is predominately expressed in cotton fiber, with significantly different expression levels in long- and short-fiber cultivars, and that GhPEL76 expression is responsive to gibberellic acid and indoleacetic acid treatment. Furthermore, GhPEL76 promoter-driven β-glucuronidase activity was detected in the roots, hypocotyls, and leaves of transgenic Arabidopsis plants, and the overexpression of GhPEL76 in transgenic Arabidopsis promoted the elongation of several organs, including petioles, hypocotyls, primary roots, and trichomes. Additionally, the virus-induced silencing of GhPEL76 in cotton reduced fiber length, and both yeast one-hybrid and transient dual-luciferase assays suggested that GhbHLH13, a bHLH transcription factor that is up-regulated during fiber elongation, activates GhPEL76 expression by binding to the G-box of the GhPEL76 promoter region. Therefore, these results suggest GhPEL76 positively regulates fiber elongation and provide a basis for future studies of cotton fiber development.