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Recently, Professor Chen Yuling’s team from the School of Life Sciences at our university made a significant breakthrough in the field of stomatal movement regulation. Their research findings, titled "Dynamic phosphorylation of RopGEF2 by MPK3/6 kinases fine-tunes diurnal stomatal movements in Arabidopsis," have been published in the prestigious international academic journal The Plant Cell (Impact Factor = 11.6).

Stomata on the surface of plant leaves serve as channels for the exchange of water and CO₂ between plants and their environment, thereby regulating two critical physiological processes: transpiration and photosynthesis. Stomatal movement not only provides the driving force for water and nutrient uptake by roots but also directly affects the rate of photosynthesis. However, important scientific questions remain unresolved in this field: Under conditions of insufficient environmental water, how do plants appropriately reduce water loss while ensuring adequate CO₂ supply for photosynthesis, thus improving water use efficiency? Furthermore, given that stomatal aperture under light exhibits a diurnal rhythm of first increasing and then decreasing, do guard cells, in addition to providing the driving force for stomatal opening, also initiate a "braking" mechanism to limit excessive opening and prevent excessive water loss?

In previous studies, Professor Chen’s team discovered that the guanine nucleotide exchange factor RopGEF2 negatively regulates light-induced stomatal opening. Building on this foundation, the team further investigated the contribution of RopGEF2 to the diurnal rhythm of stomatal opening and its activity regulation mechanism. The study revealed that light induces changes in both the activity of MPK3/6 kinases and the phosphorylation level of RopGEF2 in guard cells, following a pattern consistent with stomatal aperture: rising first and then falling. Moreover, MPK3/6 was found to phosphorylate RopGEF2 at Serine 18 (Ser18) and Serine 352 (Ser352) sites. Notably, these two sites exhibit a sophisticated division of labor: phosphorylation at Ser18 enhances the protein stability of RopGEF2, preventing light-induced degradation, while phosphorylation at Ser352 boosts its guanine nucleotide exchange activity. This dual phosphorylation mechanism enables dynamic changes in both the abundance and activity of RopGEF2 in guard cells, precisely limiting excessive stomatal opening. Consequently, it effectively prevents excessive water loss while ensuring the gas exchange required for photosynthesis, thereby improving plant water use efficiency. These findings not only enrich the understanding of negative regulatory mechanisms of stomatal movement under light but also provide new evidence for the signaling networks enabling plants to adapt to their environment. Given the critical impact of stomatal regulation on crop drought tolerance and water use efficiency, the MPK3/6-RopGEF2 module holds promise as a novel molecular target for future breeding of crops with high water use efficiency.

Dr. Yuan Yaxin, a doctoral student at the School of Life Sciences of our university, is the first author of the paper. Professor Chen Yuling, Professor Zou Yanmin, and Professor Zhang Chunguang serve as co-corresponding authors. This work was supported by the National Natural Science Foundation of China.

Paper Link:

https://academic.oup.com/plcell/advance-article/doi/10.1093/plcell/koag082/8529286