Meristem-localized inducible expression of a UDP-glycosyltransferase gene is essential for growth and development in pea and alfalfa

PsUGT1, which encodes a microsomal UDP-glucuronosyltransferase, was cloned from root tips of Pisum sativum. PsUGT1 expression is correlated with mitos is and strongly induced in dividing cells. A region at the C terminus of th e encoded protein is closely related to the UDP-glucuronic acid binding sit e consensus sequence, and the protein encoded by PsUGT1 catalyzes conjugati on of UDP-glucuronic acid to an unknown compound. Overexpression of PsUGT1 sense mRNA has no detectable effect on transgenic pea hairy root cultures o r regenerated alfalfa. However, inhibiting PsUGT1 expression by the constit utive expression of antisense mRNA (under the control of the cauliflower mo saic virus 35S promoter) markedly retards growth and development of transge nic alfalfa. Cell structure and organization in the antisense plants are si milar to those of controls, but plant growth is reduced and development is delayed. This inhibition in growth is correlated with a twofold delay in th e time required for completion of a cell cycle and with a >99% inhibition o f border cell production. Inhibition of PsUGT1 expression by meristem-local ized inducible expression of PsUGT1 antisense mRNA (under the control of it s own promoter) is lethal both in pea hairy roots and in transgenic alfalfa plants. These results indicate that PsUGT1 expression is required for norm al plant growth and development, and they are consistent with the hypothesi s that this UDP-glycosyltransferase regulates activity of a ligand(s) neede d for cell division.