ABA-cytokinin crosstalk regulate drought tolerance in Ziziphus jujuba var. spinosa through the phenylpropanoid pathway: insights from physiological and multi-omics integration.

Drought stress is a major constraint in jujube production. Although abscisic acid (ABA) and cytokinin exert opposing effects on plant growth, recent findings revealed that their combined application enhanced drought tolerance in jujube; however, the underlying mechanism remains elusive. In this study, three exogenous treatments were applied to sour jujube seedlings under drought stress: 5 mg L-1 ABA, a cytokinin mixture of 50 mg L-1 6-benzylaminopurine (6-BA) and 100 mg L-1 kinetin (KT), and a combined ABA and cytokinins solution. Transcriptomic and metabolomic analyses were integrated to elucidate how ABA and cytokinins jointly modulate drought responses. The results showed that ABA induced stem thickening, enhanced osmotic regulation and antioxidant capacity, upregulated the expression of cytochrome P450 84A1-like (CYP84A1) involved in lignin biosynthesis, and downregulated cinnamyl alcohol dehydrogenase (CAD). In contrast, cytokinins promoted stem elongation by upregulating elongation factor 2 and L-lactate dehydrogenase B, downregulating anthocyanin synthase (ANS) and peroxidase, and altering galactose/starch metabolism, thereby prioritizing growth at the expense of stress tolerance. The combined treatment reconciled these opposing effects, enhancing stress defense without compromising cytokinin-mediated growth advantage, inducing 3018 differential genes and 285 metabolites. The phenylpropanoid biosynthesis pathway was identified as central to ABA-cytokinin crosstalk, with upregulation of two CADs contributing to drought resistance and four genes encoding CAD, peroxidase, and cinnamate 4-hydroxylase (C4H) playing a critical role in this crosstalk. Additionally, beta-glucosidase 18 (BGLU18) was identified as a candidate gene correlated with 13 phenylpropanoids. Our findings reveal the molecular link between the phenylpropanoid pathway and ABA-cytokinin crosstalk in jujube drought tolerance.