A Transcript Profiling Approach Reveals an Abscisic Acid-Specific Glycosyltransferase (UGT73C14) Induced in Developing Fiber of <i>Ligon lintless-2</i> Mutant of Cotton (<i>Gossypium hirsutum</i> L.)

<div><p><i>Ligon lintless-2</i>, a monogenic dominant cotton (<i>Gossypium hirsutum</i> 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 <i>Ligon lintless-2</i> 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 <i>Escherichia coli</i> 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 donors. 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 <i>in vivo</i> 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 <i>Li</i>_<i>2</i> mutant line and may be involved in the regulation of ABA homeostasis.</p>