PIP2;1 aquaporin promotes early stomatal closure in grapevine leaves during water stress

Aquaporins play a key role in plant responses to drought. Our previous work showed limited embolism in grapevine leaves under mild water stress and suggested that the outside-xylem water pathway plays a dominant role in reducing leaf hydraulic conductance (Kleaf) during dehydration. We used CRISPR-Cas9 to knockout the PIP2;1 aquaporin encoding gene in Vitis vinifera cv. Chardonnay to study how leaf function during dehydration is affected by this aquaporin isoform. We measured functional responses like stomatal and photosynthetic responses as well as Kleaf to compare wild-type and two independent PIP2;1 knockout lines. Under moderate drought, mutants maintained greater stomatal conductance (gs) and photosynthetic rates as {Psi}w declined. No significant differences were observed in mesophyll conductance (gm) across genotypes, however, mutants exhibited slightly higher values under moderate drought. Interestingly, all lines exhibited similar Kleaf vulnerabilities to drought. Our findings show that PIP2;1 induces earlier stomatal closure during dehydration while not modulating Kleaf responses across genotypes. This rapid response in WT plants would prevent further water loss that would lead to higher xylem tensions that can lead to embolism. These findings show that multiple mechanisms collectively limit leaf gas exchange and water loss during dehydration, enhancing our understanding of plant resilience to changing environments.