Characterization of PIP2 aquaporins in Saccharum hybrids
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Aquaporins (AQPs) are proteins that facilitate the transport of water, small neutral solutes and gases across membranes and have an important role in plant physiology and drought stress responses. The sugarcane (Saccharum spp.) transcriptome was searched for AQPs, also known as major intrinsic proteins. Phylogenetic analysis based on nucleotide sequences identified 33 isoforms that fit into four AQP subfamilies previously described for monocotyledonous: 13 plasma membrane intrinsic protein (PIPs), 11 tonoplast intrinsic proteins (TIPs), six nodulin 26-like intrinsic proteins (NIPs) and three small basic intrinsic proteins (SIPs). Among the PIPs, five proteins were classified as PIP1 type and eight were classified as PIP2 type. The expression profiles of three PIP2 isoforms (ShPIP2;1, ShPIP2;5 and ShPIP2;6), which are counterparts of previously described isoforms involved in drought stress in leaves of higher plants, were aligned with monocots and dicot PIP2 protein sequence showing high identity with maize proteins. Furthermore, the transcript abundance of these three genes was evaluated through quantitative PCR (qPCR) in two sugarcane genotypes ('IACSP94-2094' and 'IACSP97-7065') subjected to water deficit under field and greenhouse conditions. ShPIP2;1, ShPIP2;5 and ShPIP2;6 isoforms were responsive to water deficit and their expression patterns were dependent on genotype, experimental condition and duration of drought stress. Taken together, our results show that the three APQs have their expression in leaves changed under drought, suggesting that these proteins constitute an important target for functional characterization in sugarcane, particularly focusing the performance of plants under varying water availability.