Abstract
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.
Highlights
Cotton (Gossypium hirsutum) fiber develops from a single epidermal cell of the seed coat
Owing to its exceptional cell length and simple secondary cell wall composition, cotton fiber provides an excellent model for studies of plant cell elongation and cell wall biogenesis (Kim and Triplett, 2001)
The cotton WLIM1a protein is a 190-amino acid protein that comprises of a short N-terminal domain (Nt, 9 amino acids), two typical LIM domains (D1 and D2; 56 amino acids each) separated by a 44-amino acid linker sequence L, and a C-terminal domain (Ct, 25 amino acids) (Figure 1A)
Summary
Cotton (Gossypium hirsutum) fiber develops from a single epidermal cell of the seed coat. Fiber development can be divided into four overlapping stages: initiation, elongation, secondary wall deposition, and maturation (Graves and Stewart, 1988). Growth and development in these stages determine fiber properties. Fiber elongation determines length while secondary wall synthesis determines traits of fineness and strength. Owing to its exceptional cell length and simple secondary cell wall composition, cotton fiber provides an excellent model for studies of plant cell elongation and cell wall biogenesis (Kim and Triplett, 2001). Significant progress has been made in large-scale identification of genes and proteins in-
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