The two domains of cotton WLIM1a protein are functionally divergent.

Our previous study demonstrated that WLIM1a has dual roles in fiber elongation and secondary cell wall synthesis in upland cotton, and the protein acts either as an actin-binding protein or as a transcription factor. Because WLIM1a consists of two different LIM domains, it is possible that these elements contribute differentially to the dual functions of the protein. In this study, we dissected the two LIM domains and characterized their biochemical functions. By using red fluorescent protein (RFP) fusion, co-sedimentation, and DNA binding methods, we found that the two domains of WLIM1a, domain1 (D1) and domain2 (D2), possessed different biochemical properties. While D1 contributed primarily to the actin filament-bundling activity of WLIM1a, D2 contributed to the DNA-binding activity of the protein; both D1 and D2 relied on a linker sequence for their activities. In addition, we found that WLIM1a and its two LIM domains form dimers in vitro. These results may lead to a better understanding of the molecular mechanisms of dual functions of WLIM1a during cotton fiber development.