Pyrabactin regulates root hydraulic properties in maize seedlings by affecting PIP aquaporins in a phosphorylation-dependent manner.

Pyrabactin, an agonist of abscisic acid (ABA), has led to the isolation and characterization of pyrabactin resistance 1/pyrabactin resistance 1-like (PYR1/PYLs) ABA receptors in Arabidopsis, which has well explained ABA-mediated stomatal movement and stress-related gene expression. In addition to inducing stomatal closure and inhibiting transpiration, ABA can also enhance root hydraulic conductivity (Lpr), thus maintaining water balance under water deficiency-related stress, but its molecular mechanism remains unclear. In the present study, the root hydraulic properties of maize seedlings in response to pyrabactin were compared to those caused by ABA. Similar to ABA, lower concentration of pyrabactin induced a remarkable increase in Lpr as well as in the gene expression of the plasma membrane intrinsic protein (ZmPIP) aquaporin and in the ZmPIP2; 1/2; 2 protein abundance. The pyrabactin-induced enhancement of Lpr was abolished by H2O2 application, indicating that pyrabactin regulates Lpr by modulating ZmPIP at transcriptional, translational and post-translational (activity) level. Pyrabactin-mediated water transport and ZmPIP gene expression were phosphorylation-dependent, suggesting that ABA-PYR1-(PP2C)-protein kinase-AQP signaling pathway may be involved in this process. As we know this is the first established ABA signaling transduction pathway that mediated water transport in roots. This observation further addressed the importance of PYR1/PYLs ABA receptor in regulating plant water use efficiency from the under ground level. Except inhibiting transpiration in leaves, our result introduces the exciting possibility of application ABA agonists for regulating roots water uptake in field, with a species- and dose dependent manner.