GhMYB1 regulates SCW stage-specific expression of the GhGDSL promoter in the fibres of Gossypium hirsutum L

Secondary cell wall (SCW) biosynthesis is an important stage of the cotton fibre development, and its transcriptional regulation is poorly understood. We selected the Gossypium hirsutum GDSL (GhGDSL) lipase/hydrolase gene (CotAD_74480), which is expressed during SCW biosynthesis (19 through to 25 days postanthesis; DPA), for study. T₁ -transgenic cotton lines expressing the β-glucuronidase (gus) reporter under the control of a 1026-bp promoter fragment of GhGDSL (P_GhGDSL ) showed 19 DPA stage-specific increase in GUS expression. 5' deletion indicated that the 194-bp fragment between -788 and -594 relative to the transcription start site was essential for this stage-specific expression. Site-directed mutagenesis of eight transcription factor binding sites within P_GhGDSL demonstrated that the MYB1AT motif (AAACCA) at -603/-598 was critical for the 19 DPA-specific reporter gene expressions. Yeast one-hybrid (Y1H) analysis identified nine proteins, including GhMYB1 (CotAD_64719) that bound to the P_GhGDSL promoter. Further, Y1H experiments using the 5' promoter deletions and individually mutated promoter motifs indicated that GhMYB1 interacted with P_GhGDSL at MYB1AT sequence. GhMYB1 was expressed specifically in fibre from 19 DPA, overlapping with the sharp rise in GhGDSL expression, indicating that it could regulate GhGDSL during fibre development. Analysis of genes co-expressed with GhMYB1 showed that it potentially regulates a number of other 19-25 DPA-specific genes in networks including those functioning in the cell wall and precursor synthesis, but not the major polysaccharide and protein components of the fibre SCW. GhGDSL and its promoter are therefore potential tools for the improvement of cotton fibre quality traits.