The Plant Cell, Vol. 25: 4281, November 2013, www.plantcell.org ã 2013 American Society of Plant Biologists. All rights reserved.

IN BRIEF

Towards Breeding Strong but Fine Cotton Fibers with a Little Help from WLIM1a The cotton (Gossypium hirsutum) fibers in that comfy sweater of yours developed from single epidermal cells of the cotton seed coat. Mature cotton fiber cells are extremely long (up to 3 to 5 cm). During the fast elongation stage, the length of the cotton fiber increases to 1000 to 3000 times the diameter of the cell (Meinert and Delmer, 1977). Accomplishing this task requires the formation of actin bundles, which serve as tracks to transport the large amount of materials needed for fiber elongation. The fast elongation stage ends with a reactive oxygen species burst, leading to the onset of secondary cell wall synthesis. Indeed, a cotton fiber is primarily occupied by the secondary wall, which mainly consists of cellulose and some minor noncellulosic carbohydrates. While a fair amount is known about cotton cell elongation (Li et al., 2013), little is known about secondary wall formation, a process that largely determines the fineness and strength of the fiber. Not surprisingly, a negative correlation is often observed between cotton fiber fineness and strength; the concurrent improvement of these traits represents a bottleneck in cotton breeding. In the process of unraveling the mechanism underlying secondary cell wall formation in cotton, Han et al. (pages 4421–4438) characterized a protein whose expression simultaneously increases fiber fineness and strength. Specifically, the authors aimed to identify and elucidate the function of a LIM-domain protein, WLIM1a, in cotton, which they suspected would function in fiber development. LIM-domain proteins are small (;200–amino acid) proteins that are widely distributed in eukaryotes and contain two LIM domains separated by a long (40– to 50–amino acid) linker. The LIM domain is an evolutionarily conserved double zinc-finger motif. In animals, nuclear LIM-domain proteins act primarily in tissue-specific gene regulation and cell fate determination, whereas cytoplasmic LIM-domain proteins function mainly in cytoskeletal organization. While LIM-domain proteins have been identified in various plants and have been shown to function in cytoskeletal www.plantcell.org/cgi/doi/10.1105/tpc.113.251110

Scanning electron micrographs of the surfaces of wild-type (WT) and WLIM1a-overexpressing fibers. Bar = 5 mm. (Reprinted from Han et al. [2013], Figure 3D.)

organization and transcriptional regulation (Moes et al., 2013), our knowledge of the physiological roles of plant LIM-domain proteins remains limited. Han and colleagues determined that WLIM1a is preferentially expressed during the elongation and secondary cell wall synthesis stages in developing cotton fibers, making WLIM1a a target for further study. They found that the fibers of WLIM1aunderexpressing plants were not obviously altered in terms of length or other fiber properties. By contrast, WLIM1a-overexpressing plants had long fibers. The secondary walls of these fibers were much thinner and more compact than those of the wild type, with reduced microfibril angles and a smoother, more uniform arrangement of fibrils, as determined by scanning electron microscopy (see figure) and x-ray diffraction analysis. WLIM1a probably contributes to rapid fiber elongation via its function in actin filament bundling. Unexpectedly, the fiber phenotype observed in the WLIM1a-overexpressing plants is likely due to the presence of increased levels of lignin/lignin-like phenolics. WLIM1a may respond to the reactive oxygen species burst that terminates fiber elongation by entering the nucleus, where it serves as a transcription factor to activate the expression of genes in the phenylpropanoid biosynthesis pathway. Thus, WLIM1a may play an important role in the crosstalk between the processes of cell elongation and secondary wall synthesis in developing cotton fibers.

Importantly, the formation of the thin, compact secondary cell walls in WLIM1aoverexpressing fibers resulted in simultaneous improvement of fiber fineness and strength, making WLIM1a (or other genes involved in the biosynthesis of lignin/lignin-like phenolics) a promising target for cotton breeding. Your next cotton sweater may be softer and stronger than the one you’re wearing now. Jennifer Lockhart Science Editor [email protected] REFERENCES Han, L.B., Li, Y.B., Wang, H.Y., Wu, X.M., Li, C.L., Luo, M., Wu, S.J., Kong, Z.S., Pei, Y., Jiao, G.L., and Xia, G.X. (2013). The dual functions of WLIM1a in cell elongation and secondary wall formation in developing cotton fibers. Plant Cell 25: 4421–4438. Li, X.M., Yuan, D.J., Zhang, J.F., Lin, Z.X., and Zhang, X.L. (2013). Genetic mapping and characteristics of genes specifically or preferentially expressed during fiber development in cotton. PLoS ONE 8: e54444. Meinert, M.C., and Delmer, D.P. (1977). Changes in biochemical composition of the cell wall of the cotton fiber during development. Plant Physiol. 59: 1088–1097. Moes, D., Gatti, S., Hoffmann, C., Dieterle, M., Moreau, F., Neumann, K., Schumacher, M., Diederich, M., Grill, E., Shen, W.H., Steinmetz, A., and Thomas, C. (2013). A LIM domain protein from tobacco involved in actin-bundling and histone gene transcription. Mol. Plant 6: 483–502.

Towards Breeding Strong but Fine Cotton Fibers with a Little Help from WLIM1a Jennifer Lockhart Plant Cell 2013;25;4281; originally published online November 12, 2013; DOI 10.1105/tpc.113.251110 This information is current as of March 18, 2015 References

This article cites 4 articles, 2 of which can be accessed free at: http://www.plantcell.org/content/25/11/4281.full.html#ref-list-1

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Towards breeding strong but fine cotton fibers with a little help from WLIM1a.

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