Abstract
The secondary cell wall in mature cotton fibers contains over 90% cellulose with low quantities of xylan and lignin. However, little is known regarding the regulation of secondary cell wall biosynthesis in cotton fibers. In this study, we characterized an R2R3-MYB transcription factor, GhMYB7, in cotton. GhMYB7 is expressed at a high level in developing fibers and encodes a MYB protein that is targeted to the cell nucleus and has transcriptional activation activity. Ectopic expression of GhMYB7 in Arabidopsis resulted in small, curled, dark green leaves and also led to shorter inflorescence stems. A cross-sectional assay of basal stems revealed that cell wall thickness of vessels and interfascicular fibers was higher in transgenic lines overexpressing GhMYB7 than in the wild type. Constitutive expression of GhMYB7 in Arabidopsis activated the expression of a suite of secondary cell wall biosynthesis-related genes (including some secondary cell wall-associated transcription factors), leading to the ectopic deposition of cellulose and lignin. The ectopic deposition of secondary cell walls may have been initiated before the cessation of cell expansion. Moreover, GhMYB7 was capable of binding to the promoter regions of AtSND1 and AtCesA4, suggesting that GhMYB7 may function upstream of NAC transcription factors. Collectively, these findings suggest that GhMYB7 is a potential transcriptional activator, which may participate in regulating secondary cell wall biosynthesis of cotton fibers.
Highlights
Cotton fibers, the world’s most important natural textile material, are single-cell protrusions originating from individual epidermal cells of the ovules
These findings suggest that GhMYB7 is a potential transcriptional activator, which may participate in regulating secondary cell wall biosynthesis of cotton fibers
Sequence alignment showed that the GhMYB7 amino acid sequence shared high similarity with AtMYB26 and AtMYB103, which have been shown to positively regulate secondary cell wall (SCW) biosynthesis in Arabidopsis (Yang et al, 2007; Zhong et al, 2008)
Summary
The world’s most important natural textile material, are single-cell protrusions originating from individual epidermal cells of the ovules. Fiber development can be divided into four distinct but overlapping phases, that is, fiber initiation, primary cell-wall formation, secondary cell-wall thickening, and maturation (Basra and Mailk, 1984). The secondary cell wall (SCW) of the mature fiber consists of over 90% cellulose, with low quantities of xylan and lignin (Haigler et al, 2012; Han et al, 2013). Deposition of >90% cellulose in cotton fiber cell walls during the SCW thickening stage makes this unique cell valuable in understanding the regulation of plant cell wall biogenesis. Only one study has elucidated the role of a MYB protein in SCW biosynthesis of cotton fibers (Sun et al, 2015)
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