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

Summary 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 ( Gh GDSL ) lipase/hydrolase gene (Cot AD _74480), which is expressed during SCW biosynthesis (19 through to 25 days postanthesis; DPA ), for study. T 1 ‐transgenic cotton lines expressing the β‐glucuronidase ( gus ) reporter under the control of a 1026‐bp promoter fragment of Gh GDSL ( P G h GDSL ) 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 G h GDSL demonstrated that the MYB 1 AT motif ( AAACCA ) at –603/–598 was critical for the 19 DPA ‐specific reporter gene expressions. Yeast one‐hybrid (Y1H) analysis identified nine proteins, including Gh MYB 1 (Cot AD _64719) that bound to the P G h GDSL promoter. Further, Y1H experiments using the 5′ promoter deletions and individually mutated promoter motifs indicated that Gh MYB 1 interacted with P G h GDSL at MYB 1 AT sequence. Gh MYB 1 was expressed specifically in fibre from 19 DPA , overlapping with the sharp rise in Gh GDSL expression, indicating that it could regulate Gh GDSL during fibre development. Analysis of genes co‐expressed with Gh MYB 1 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 . Gh GDSL and its promoter are therefore potential tools for the improvement of cotton fibre quality traits.