Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 15, 2013
Publication Date: September 23, 2013
Citation: Gilbert, M.K., Bland, J.M., Shockey, J.M., Cao, H., Hinchliffe, D.J., Fang, D.D., Naoumkina, M.A. 2013. A transcript profiling approach reveals an abscisic acid specific glycosyltransferase (UGT73C14) induced in developing fiber of Ligon lintless-2 mutant of cotton (Gossypium hirsutum L.). PLoS One. 8(9):e75268. Interpretive Summary: Glycosyltransferases transfer sugars to a wide range of acceptors, from hormones and secondary metabolites to chemicals and toxins in the environment. Glycosylation reactions serve to convert reactive molecules into more stable and non-reactive storage forms. Glycosylation also serves as a regulatory step in homeostasis of plant hormones. Despite the importance of hormone regulation in cotton fiber development processes, to date, no cotton glycosyltransferase involved in these processes has been characterized at the molecular level. The aim of this study was to find and characterize cotton glycosyltransferase involved in regulation of cotton fiber development. Using transcript profiling and substrates screening approach, we identified cotton glycosyltransferase that was able to glycosylate abscisic acid. Studies in plant system confirmed activity of this glycosyltransferase against of abscisic acid, suggesting its role in abscisic acid homeostasis in cotton. Abscisic acid is a plant hormone that plays important roles in many biological processes including seed development, dormancy, germination, vegetative growth, and environmental stress responses. However, the inhibitory effect of abscisic acid on cotton fiber development has also been well-documented. Increased glycosylation of abscisic acid during cotton fiber development can improve fiber quality. Therefore, this glycosyltransferase is a good candidate for genetic manipulations to improve fiber quality.
Technical Abstract: Ligon lintless-2, a monogenic dominant cotton (Gossypium hirsutum L.) fiber mutation, causing extreme reduction in lint fiber length with no pleiotropic effects on vegetative growth, represents an excellent model system to study fiber elongation. A UDP-glycosyltransferase that was highly expressed in developing fibers of the mutant Ligon lintless-2 was isolated. The predicted amino acid sequence showed ~53% similarity with Arabidopsis UGT73C sub-family members and the UDP-glycosyltransferase was designated as UGT73C14. When expressed in Escherichia coli as a recombinant protein with a maltose binding protein tag, UGT73C14 displayed enzymatic activity toward ABA and utilized UDP-glucose and UDP-galactose as the sugar donor. The recombinant UGT73C14 converted natural occurring isoform (+)-cis, trans-ABA better than (+)-trans, trans-ABA and (-)-cis, trans-ABA. Transgenic Arabidopsis plants constitutively overexpressing UGT73C14 did not show phenotypic changes under standard growth conditions. However, the increased glycosylation of ABA resulted in phenotypic changes in post-germinative growth and seedling establishment, confirming in vivo activity of UGT73C14 for ABA. This suggests that the expression level of UGT73C14 is regulated by the observed elevated levels of ABA in developing fibers of the Li2 mutant line and may be involved in the regulation of ABA homeostasis.