Mature cotton fiber secondary cell wall comprises largely of cellulose (> 90%) and small amounts of xylan and lignin. Little is known about the cotton fiber xylan biosynthesis by far. To comprehensively survey xylan biosynthetic genes in cotton fiber, we identified five IRX9, five IRX10, one IRX14, six IRX15, two FRA8, one PARVUS, eight GUX, four GXM, two RWA, two AXY9, 13 TBL genes by using phylogenetic analysis coupled with expression profile analysis and co-expression analyses. In addition, we also identified two GT61 members, two GT47 memb...