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Modification of the expression of the aquaporin ZmPIP2;5 affects water relations and plant growth
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Edité par CCSD ; Oxford University Press ; American Society of Plant Biologists -
International audience. In maize (Zea mays), the plasma membrane intrinsic protein PIP2;5 is the most highly expressed aquaporin in roots. Here, we investigated how deregulation of PIP2;5 expression affects water relations and growth using maize overexpressing (OE; B104 inbred) or knockout (KO; W22 inbred) lines. The hydraulic conductivity of the cortex cells of roots grown hydroponically was higher and lower in PIP2;5 OE and pip2;5 KO lines, respectively, compared with their corresponding wild-type (WT) plants. While whole root conductivity decreased in the KO lines compared to the WT, no difference was observed in OE plants. This paradox was interpreted using the MECHA hydraulic model, which computes the radial flow of water within root sections. The model hints that the plasma membrane permeability of the cells is not radially uniform but PIP2;5 may be saturated in cell layers with apoplastic barriers, i.e. the endodermis and exodermis, suggesting the presence of post-translational mechanisms controlling the abundance of PIP in the plasma membrane in these cells. At the leaf level, where the PIP2;5 gene is lowly expressed in WT plants, the hydraulic conductance was higher in the PIP2;5 OE lines compared with the WT plants, whereas no difference was observed in the pip2;5 KO lines. The temporal trend of leaf elongation rate used as a proxy of that of xylem water potential was faster in PIP2;5 OE plants upon mild stress, but not in well-watered condition, demonstrating that PIP2;5 may play a beneficial role for plant growth under specific conditions.
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