Isolation of Six Novel Aquaporin Genes from Triticum aestivum L. and Functional Analysis of TaAQP6 in Water Redistribution

Abstract

Water transport through the cell membranes is regulated largely by a family of proteins known as aquaporins (AQPs). In this study, six novel aquaporin genes, TaAQP1∼TaAQP6, were isolated from the common wheat Triticum aestivum L. var. Changle 5. These six TaAQPs share common features with other plant AQPs. Three of them (TaAQP2, 3, and 4) phylogenetically belong to plant PIP2 group, and the other three resemble proteins from PIP1(TaAQP1), TIP1(TaAQP6), and TIP2(TaAQP5) groups, respectively. The subcellular localization assay, determined by onion epidermal cell transient expression system, indicated that TaAQP6 is a membrane-associated protein. Transformation of TaAQP6 into Xenopus oocytes demonstrated that it facilitated water uptake, suggesting that this TaAQP is an active membrane-associated protein. The expression of TaAQP6 was upregulated in shoots of wheat seedlings, but downregulated in roots under polyethylene glycol (PEG) stress. In split-root experiment, the amount of TaAQP6 transcripts decreased in dry roots (cultured in PEG solution), but increased in wet roots (cultured in water), and remained unchanged in shoots. It is interesting to note that the osmolality changes of different parts in PEG-treated and split-root seedlings were related to the expression of TaAQP6. Taken together, we proposed that TaAQP6 participates in internal water redistribution of wheat seedlings during osmotic stress by regulating outflow of water from water-rich organs to the parts with poor water status under water deficit condition.