Abstract
Aquaporins are channel proteins which transport water across cell membranes. We show that the bread wheat aquaporin gene TaTIP2;2 maps to the long arm of chromosome 7b and that its product localizes to the endomembrane system. The gene is expressed constitutively in both the root and the leaf, and is down-regulated by salinity and drought stress. Salinity stress induced an increased level of C-methylation within the CNG trinucleotides in the TaTIP2;2 promoter region. The heterologous expression of TaTIP2;2 in Arabidopsis thaliana compromised its drought and salinity tolerance, suggesting that TaTIP2;2 may be a negative regulator of abiotic stress. The proline content of transgenic A. thaliana plants fell, consistent with the down-regulation of P5CS1, while the expression of SOS1, SOS2, SOS3, CBF3 and DREB2A, which are all stress tolerance-related genes acting in an ABA-independent fashion, was also down-regulated. The supply of exogenous ABA had little effect either on TaTIP2;2 expression in wheat or on the phenotype of transgenic A. thaliana. The expression level of the ABA signalling genes ABI1, ABI2 and ABF3 remained unaltered in the transgenic A. thaliana plants. Thus TaTIP2;2 probably regulates the response to stress via an ABA-independent pathway(s).
Highlights
A range of abiotic stresses, including soil salinity, drought and extreme temperature, can compromise crop yield and quality
Their structure is characterized by the formation of six transmembrane domains connected by five loops [2,3,4]. Based on their sub-cellular localization and sequence, plant aquaporins have been classified into four sub-families, namely the plasma membrane intrinsic proteins (PIPs), the tonoplast intrinsic proteins (TIPs), the nodulin 26-like intrinsic proteins (NIPs) and the small basic intrinsic proteins [5]
We have determined its chromosomal location and confirmed that its expression is suppressed by both drought and salinity stress. We show that it encodes a protein deposited in the endomembrane, and that its heterologous expression in A. thaliana compromised the level of tolerance to salinity and drought stress
Summary
A range of abiotic stresses, including soil salinity, drought and extreme temperature, can compromise crop yield and quality. Improving tolerance to these stresses is a major priority in many crop breeding programmes. The aquaporins belong to a highly conserved major intrinsic protein family, and combine with the cell membrane system to control the flow of water between and within the cell. Their structure is characterized by the formation of six transmembrane domains connected by five loops [2,3,4]. There are three new subclasses of aquaporins in moss Physcomitrella patens, named GlpF-like intrinsic protein (GIP), hybrid intrinsic protein (HIP) and X intrinsic protein (XIP) [6]
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