Crosstalk between Ethylene, Jasmonate and ABA in Response to Salt Stress during Germination and Early Plant Growth in Cucurbita pepo

The crosstalk of phytohormones in the regulation of growth and development and the response of plants to environmental stresses is a cutting-edge research topic, especially in crop species. In this paper, we study the role and crosstalk between abscisic acid (ABA), ethylene (ET), and jasmonate (JA) in the control of germination and seedling growth in water or in standard nutrient solution and under salt stress (supplemented with 100-200 mM NaCl). The roles of ET and JA were studied using squash ET- and JA-deficient mutants aco1a and lox3a, respectively, while the crosstalk between ET, JA, and ABA was determined by comparing the expression of the key ABA, JA, and ET genes in wild-type (WT) and mutant genotypes under standard conditions and salt stress. Data showed that ET and JA are positive regulators of squash germination, a function that was found to be mediated by downregulating the ABA biosynthesis and signaling pathways. Under salt stress, aco1a germinated earlier than WT, while lox3a showed the same germination rate as WT, indicating that ET, but not JA, restricts squash germination under unfavorable salinity conditions, a function that was also mediated by upregulation of ABA. ET and JA were found to be negative regulators of plant growth during seedling establishment, although ET inhibits both the aerial part and the root, while JA inhibits only the root. Both aco1a and lox3a mutant roots showed increased tolerance to salt stress, a phenotype that was found to be mainly mediated by JA, although we cannot exclude that it is also mediated by ABA.