Abstract
The absorption of soil water by roots allows plants to maintain their water status. At the endodermis, water transport can be affected by initial formation of a Casparian strip, and further deposition of suberin lamellas and regulated by the function of aquaporins. Four Casparian strip membrane domain protein-like (CASPL) (CASPL1B1, CASPL1B2, CASPL1D1 and CASPL1D2) were previously shown to interact with PIP2;1, (Bellati et al. 2016). The present work shows that CASPL1B1, CASPL1B2 and CASPL1D2 are exclusively expressed in suberized endodermal cells, suggesting a cell-specific role in suberization and/or water transport regulation. When compared to wild-type plants, and by contrast to caspl1b1*caspl1b2 double loss-of-function, caspl1d1*caspl1d2 double mutants showed, in some control or NaCl stress experiments and not upon ABA treatment a weak enlargement of the continuous suberization zone. None of the mutants showed root hydraulic conductivity (Lpr ) phenotype, whether in control, NaCl or ABA treatment conditions. The data suggest a slight negative role for CASPL1D1 and CASPL1D2 in suberization under control or salt stress conditions, with no major impact on whole root transport functions. At the molecular level, CASPL1B1 was able to physically interact with PIP2;1, and potentially could influence the regulation of aquaporins by acting on their phosphorylated form.