The maize aquaporin ZmPIP1;6 enhances stomatal opening and CO2- and ABA-induced stomatal closure

The plasma membrane aquaporin ZmPIP1;6 is expressed in maize stomatal complexes, with higher expression during the day than at night. To elucidate the role of ZmPIP1;6 in gas exchange and stomatal movement, it was expressed in maize (inbred line B104) under the control of p35S promoter (OE) or its native promoter fused with mYFP cDNA (mYFP-ZmPIP1;6). In stomatal complexes of the leaf mature zone, mYFP-ZmPIP1;6 showed higher expression in subsidiary cells than in guard cells, with light and dark treatments influencing its subcellular localization. Notably, ZmPIP1;6 internalization increased in dark conditions versus light. Stomatal opening was greater in ZmPIP1;6 OE than in wild type (WT), while closure exhibited greater sensitivity to elevated CO2 concentration or ABA treatment. Our finding revealed that reactive oxygen species (H2O2) was involved in ABA-induced stomatal closure, while ZmPIP1;6 was unable to facilitate H2O2 diffusion when expressed in yeast. Finally, ZmPIP1;6 OE and mYFP-ZmPIP1;6 transgenic plants exhibited higher abaxial stomatal density than WT. Overall, these results indicate that ZmPIP1;6 plays important roles in stomatal opening and CO2- and ABA-induced stomatal closure.