DEVELOPMENTAL EXPRESSION OF A TURGOR-RESPONSIVE GENE THAT ENCODES AN INTRINSIC MEMBRANE-PROTEIN

We previously reported that the pea (Pisum sativum) gene, Trg31, shows increased transcription and elevated mRNA levels in plant tissues which are dehydrated and lose turgor. The protein encoded by Trg31 is homologous to members of the MIP intrinsic membrane protein superfamily. Expression of Trg31 was characterized during pea seedling development and in transgenic tobacco using Trg31 promoter::Gus fusions. In pea, Trg31 mRNA abundance was highest in roots followed by flowers, stems and leaves. In roots, Trg31 mRNA levels were highest in non-elongating regions and low in root tips. In dark-grown seedlings, Trg31 mRNA levels were high in stems and illumination caused mRNA abundance in stems to decrease. Histochemical analysis of transgenic tobacco expressing Trg31 promoter::Gus constructs showed high GUS activity in root to shoot and hypocotyl to cotyledon junctions and cotyledons in germinating seedlings. High activity was also observed in the leaf marginal meristem and trichomes. In more mature seedlings, Trg31 promoter activity was observed in the non-elongating portion of the root and in stems especially in the vascular tissue. A gradient of expression was noted in leaf to stem junction zones with highest expression in the younger tissues. Very high expression was observed in stems of flowers and other floral tissues including the calyx, corolla, style, ovules, pods and pollen. This expression pattern suggests that the Trg31 gene product may facilitate transport from sources, through transmitting tissues to sinks.