Plasma membrane aquaporins regulate root hydraulic conductivity in the model plant Setaria viridis.

The high rate of productivity observed in panicoid crops is in part due to their extensive root system. Recently green foxtail (Setaria viridis) has emerged as a genetic model system for panicoid grasses. Natural accessions of S. viridis originating from different parts of the world, with differential leaf physiological behaviour, have been identified. This work focused on understanding the physiological and molecular mechanisms controlling root hydraulic conductivity and root-to-shoot gas-exchange signalling in S. viridis. We identified two accessions, SHA and ZHA, with contrasting behaviour at the leaf, root, and whole-plant level. Our results indicated a role for root aquaporin plasma membrane intrinsic proteins in the differential behaviour of SHA and ZHA. Moreover, a different root hydraulics response to low levels of abscisic acid between SHA and ZHA was observed, which was associated with root aquaporins (AQPs). Using cell imaging, biochemical and reverse-genetic approaches, we identified plasma membrane intrinsic protein 1; 6 (PIP1; 6) as a possible PIP1 candidate that regulates radial root hydraulics and root-to-shoot signalling of gas exchange in S. viridis. In heterologous systems, PIP1; 6 localized in the endoplasmic reticulum, and upon interaction with PIP2s, re-localization to the plasma membrane was observed. PIP1; 6 was predominantly expressed at the root endodermis. Generation of knockout PIP1; 6 plants (KO-PIP1; 6) in S. viridis showed altered root hydraulic conductivity, altered gas exchange and alteration of root transcriptional patterns. Our results indicate that PIPs are essential in regulating whole-plant water homeostasis in S. viridis. We conclude that root hydraulic conductivity and gas exchange are positively associated and are regulated by AQPs.