UDP-glucosyltransferase 71C4 regulates seed development by redistributing phenylpropanoid metabolism in cotton

Seeds are important for plant reproduction, and hence it is important to identify genes regulating seed development. Here, we focused on a member of the glycosyltransferase (GT) family, UDP-glucosyltransferase 71C4 (UGT71C4), which influences the seed width, seed length, and yield traits (lint percentage and seed index) by regulating the lignin and flavonoid pathways of phenylpropane metabolism, affects the oil and protein contents of mature seeds, and controls the seed size by regulating cell proliferation. Overexpression of UGT71C4 leads to seed enlargement by activating expression of peroxiredoxins and the flavonoid metabolism pathway; induces accumulation of ROS, which promotes cell proliferation; and significantly improves yield traits, with the seed index increasing from 10.66 to 11.91 and protein increasing by 5.34%, but oil content decreasing 8.98%. Conversely, knockout of UGT71C4 causes seeds to become smaller; the lignin metabolism pathway to be activated, especially enzymes relating to lignin synthesis leading to increased ectopic deposition of lignin in the ovule and constrained ovule growth and development; and significant improvement of yield traits, with lint percentage increasing from 39.62% to 41.94%, seed index decreasing from 10.66 to 8.60, protein content decreasing 4.28%, and no significant change in oil content. Our research provides new insights into seed size regulation through UDP-glucosyltransferase, providing potential methods for improving plant yield.