Physiological and molecular characterisation of altered root hydraulic properties in rice due to allelic variation or genetic manipulation of plasma membrane intrinsic proteins (PIPs, a class of aquaporins)

A cluster of three PIPs on chromosome 7 of rice are all candidate genes for a drought avoidance locus. These genes are highly expressed in roots and thought to have a major role in root hydraulic conductance. Natural allelic variation in hydraulic conductance has been detected in near isogenic lines differing only for this part of chromosome 7, but is only detected when plants are droughted. RNAi knockdown lines of one gene (PIP2.1) show lower hydraulic conductance irrespective of drought, while RNAi lines of PIP2.4 show no clear phenotype. We could hypothesis either that the natural variation affects hydraulic conductance only when flow rates are high (when transportation is high) or that it affects it only when the roots are dried. We want to test these hypothesis. We want to know the implications for drought avoidance since the implication is that in some scenarios, lower hydraulic conductance would have a negative impact on performance under drought, while in others it would be a benefit. In addition, we want to know more about the differences between i) genotypes, ii) wild type/transgenics and iii) well watered/droughted plants in terms of their expression and protein composition of PIP genes, a complex problem given the strong homology between PIP gene family members and the complex heterodimer nature of their existence in membranes.

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