Abstract
Plant plasma membrane intrinsic proteins (PIP) cluster in two phylogenetic groups, PIP1 and PIP2 that have different water channel activities when expressed in Xenopus oocytes. PIP2s induce a marked increase of the membrane osmotic water-permeability coefficient (Pf), whereas PIP1s are generally inactive. Here we report the cloning of two durum wheat (Triticum turgidum L. subsp. durum) cDNAs encoding TdPIP1;1 and TdPIP2;1 belonging to the PIP1 and PIP2 subfamilies, respectively. Contrary to TdPIP1;1, expression of TdPIP2;1 in Xenopus oocytes resulted in an increase in Pf compared to water-injected oocytes. Co-expression of the non-functional TdPIP1;1 and the functional TdPIP2;1 lead to a significant increase in Pf compared with oocytes expressing TdPIP2;1 alone. A truncated form of TdPIP2;1, tdpip2;1, missing the first two transmembrane domains, had no water channel activity. Nonetheless, its co-expression with the functional TdPIP2;1 partially inhibits the Pf and disrupt the activities of plant aquaporins. In contrast to the approach developed in Xenopus oocytes, phenotypic analyses of transgenic tobacco plants expressing TdPIP1;1 or TdPIP2;1 generated a tolerance phenotype towards osmotic and salinity stress. TdPIP1;1 and TdPIP2;1 are differentially regulated in roots and leaves in the salt-tolerant wheat variety when challenged with salt stress and abscisic acid. Confocal microscopy analysis of tobacco roots expressing TdPIP1;1 and TdPIP2;1 fused to the green fluorescent protein showed that the proteins were localized at the plasma membrane.
► Two cDNAs isoforms of PIPs from durum wheat have been sequenced and characterized. ► The Pf of TdPIP2;1 increased rapidly indicating that it forms a functional water channel. ► Whereas, TdPIP1;1 or truncated forms had Pf values similar to water-injected oocytes. ► TdPIP1;1 and TdPIP2;1 proteins were localized to the cell plasma membrane. ► Overexpression of TdPIP1;1 and TdPIP2;1 produced higher salt and drought tolerance.