PhD student The Hebrew University of Jerusalem Herzliya, HaMerkaz, Israel
Body of Abstract: The phytohormone abscisic acid (ABA) plays essential roles in plant growth and development, including seed maturation and germination, fruit development and ripening, and adaptation to abiotic and biotic stresses. Exposure of plants to drought and high salinity increases ABA levels, which affects gene expression. The core ABA signaling machinery consists of a family of protein receptors (PYR/PYL/RCAR), protein phosphatases (PP2Cs), and SNF1-related kinases (SnRK2s), which activate downstream genes. In tomato (Solanum lycopersicum), there are eight receptor genes, seven PP2Cs, and eight SnRK2s. The research aims to unravel the functions of specific SnRK2 kinases in developmental processes and stress signaling. To this end, we introduced mutations in all SnRK2 genes in tomato (cv M82) using CRISPR-Cas9 gene editing. Characterization of these mutants showed that ABA-regulated water retention in tomato plants is mainly mediated by SnRK2.3, which is essential for stomatal closure under water stress conditions. Tomato plants lacking SnRK2.3 produce smaller fruits with more seeds without loss of total fruit yield. Although SnRK2.3 and SnRK2.4 belong to the same subgroup of SnRK2 enzymes, SnRK2.4 is not involved in stomata closure. However, a double mutant in both genes is lethal, indicating that other essential roles of SnRK2.3 in embryonic development overlap with SnRK2.4. These results shed light on ABA signaling and pave the way for application in breeding improved drought tolerant tomato varieties.