RtNAC055 promotes drought tolerance via a stomatal closure pathway linked to methyl jasmonate/hydrogen peroxide signaling in <i>Reaumuria trigyna</i>

Abstract

The stomata regulate CO₂ uptake and efficient water usage, thereby promoting drought stress tolerance. NAC proteins (NAM, ATAF1/2, and CUC2) participate in plant reactions following drought stress, but the molecular mechanisms underlying NAC-mediated regulation of stomatal movement are unclear. In this study, a novel NAC gene from <i>Reaumuria trigyna</i>, <i>RtNAC055</i>, was found to enhance drought tolerance via a stomatal closure pathway. It was regulated by RtMYC2 and integrated with jasmonic acid signaling and was predominantly expressed in stomata and root. The suppression of <i>RtNAC055</i> could improve jasmonic acid and H₂O₂ production and increase the drought tolerance of transgenic <i>R. trigyna</i> callus. Ectopic expression of <i>RtNAC055</i> in the <i>Arabidopsis atnac055</i> mutant rescued its drought-sensitive phenotype by decreasing stomatal aperture. Under drought stress, overexpression of <i>RtNAC055</i> in poplar promoted ROS (H₂O₂) accumulation in stomata, which accelerated stomatal closure and maintained a high photosynthetic rate. Drought upregulated the expression of <i>PtRbohD/F</i>, <i>PtP5CS2</i>, and <i>PtDREB1</i>.<i>1</i>, as well as antioxidant enzyme activities in heterologous expression poplars. RtNAC055 promoted H₂O₂ production in guard cells by directly binding to the promoter of <i>RtRbohE</i>, thus regulating stomatal closure. The stress-related genes <i>RtDREB1</i>.<i>1/P5CS1</i> were directly regulated by RtNAC055. These results indicate that RtNAC055 regulates stomatal closure by maintaining the balance between the antioxidant system and H₂O₂ level, reducing the transpiration rate and water loss, and improving photosynthetic efficiency and drought resistance.