SnRK2.6 interacts with phytochrome B and plays a negative role in red light-induced stomatal opening.

Light is an important environmental factor for plant growth and development. Phytochrome B (phyB), a classical red/far-red light receptor, plays vital role in controlling plant photomorphogenesis and light-induced stomatal opening. Phytohormone abscisic acid (ABA) accumulates rapidly and triggers a series of physiological and molecular events during the responses to multiple abiotic stresses. Recent studies showed that phyB mutant synthesizes more ABA and exhibits improved tolerance to salt and cold stress, suggesting that a crosstalk exists between light and ABA signaling pathway. However, whether ABA signaling components mediate responses to light remains unclear. Here, we showed that SnRK2.6 (Sucrose Nonfermenting 1-Related Protein Kinase 2.6), a key regulator in ABA signaling, interacts with phyB and participates in light-induced stomatal opening. First, we checked the interaction between phyB and SnRK2s, and found that SnRK2.2/2.3/2.6 kinases physically interacted with phyB in yeast and in vitro. We also performed co-IP assay to support that SnRK2.6 interacts with phyB in plant. To investigate the role of SnRK2.6 in red light-induced stomatal opening, we obtained the snrk2.6 mutant and overexpression lines, and found that snrk2.6 mutant exhibited a significantly larger stomatal aperture under red light treatment, while the two independent overexpression lines showed significantly smaller stomatal aperture, indicative of a negative role for SnRK2.6 in red light-induced stomatal opening. The interaction of SnRK2.6 with red light receptor and the negative role of SnRK2.6 in red light-induced stomatal opening provide new evidence for the crosstalk between ABA and red light in guard cell signaling.

RIC7 plays a negative role in ABA-induced stomatal closure by inhibiting H2O2 production.

When plants encounter environmental stresses, phytohormone abscisic acid (ABA) accumulates quickly and efficiently reduces water loss by inducing stomatal closure. Reactive oxygen species (ROS) is an important regulator in ABA-induced stomatal closure, and ROS generation is modulated by multiple components in guard-cell ABA signaling. ROP interactive CRIB-containing protein 7 (RIC7) has been found to negatively regulate ABA-induced stomatal closure. However, the molecular details of the RIC7 function in this process are unclear. Here, by using two RIC7 overexpressing mutants, we confirmed the negative role of RIC7 in ABA-induced stomatal closure and found that guard cells of RIC7 overexpressing mutants generated less H2O2 than the wild type with ABA treatment, which were consistent with the reduced expression levels of ROS generation related NADPH oxidase genes AtRBOHD and AtRBOHF, and cytosolic polyamine oxidase genes PAO1 and PAO5 in the RIC7 overexpressing mutants. Furthermore, external applied H2O2 failed to rescue the defects of stomatal closure in RIC7 overexpressing mutants. These results suggest that RIC7 affects H2O2 generation in guard cells, and the function of H2O2 is dependent on RIC7 in ABA-induced stomatal closure, indicative of interdependency between RIC7 and H2O2 in ABA guard-cell signaling.