The Aquaporin Gene Family of Cotton

Aquaporin proteins are found in most living organisms and are quite diverse in plants where they function as transport systems for water and other small molecules. Plant aquaporins have been shown to be differentially regulated under environmental stress such as drought, salt and cold treatment. The plant aquaporins belong to the large major intrinsic protein (MIP) family and consist of 5 subfamilies including plasma membrane intrinsic proteins (PIP), tonoplast intrinsic proteins (TIP), NOD26-like intrinsic proteins (NIP), small basic intrinsic proteins (SIP), and the recently discovered X intrinsic protein (XIP). Using conserved domain sequences obtained by comparing cotton EST/nucleotide data with sequences from other plants, we designed degenerate PCR primers to identify the complete aquaporin PIP and TIP families in cotton (Gossypium hirsutum L.). From this molecular cloning effort together with homology search, more than 60 cotton aquaporin genes were identified. These data suggest that the cotton aquaporins are as divergent as other plant species. The cotton aquaporins consist of more than 20 members each in the PIP, TIP subfamilies while also containing fewer, more divergent members of the NIP, SIP and XIP subfamilies. To explore the physiological roles of these aquaporin genes in cotton, expression analysis was performed using semi-quantitative RT-PCR. Our results suggest the cotton aquaporin family is structurally diversified and many cotton aquaporin transcripts are regulated tissue specifically while others are expressed across tissues.