Cytokinin and auxin modulate cucumber parthenocarpy fruit development

Parthenocarpy (fruit development without pollination)is an important agricultural trait, which determines the production of horticultural crops like tomato, eggplant and cucumber. Parthenocarpy ability varies widely among cucumber lines. To better understand the genetic regulators underlying this variation, hormone and transcriptome profiles and the expressions of hormone-related genes in non-pollinated fruit of a highly parthenocarpic line DDX and a weakly parthenocarpic line ZK were compared at 1 day after anthesis. The cytokinin and gibberellic acid contents were higher in DDX than in ZK, while the abscisic acid content was less. Exogenous application of cytokinins, auxin and gibberellic acid 4 + 7 successfully induced the parthenocarpic fruit set of ZK. The transcript levels of several cytokinin biosynthesis genes (CsCYP735A1, CsCYP735A2 and CsLOG1), cytokinin-responsive genes (CsRR8/9b, CsRR8/9d, CsRR8/9e and CsRR16/17)and auxin signal transduction genes (Aux/IAAs)were greater in DDX than in ZK, while the level of an abscisic acid receptor (CsPYR1)was lower. These results suggest that high expression levels of cytokinin- and auxin-related genes in DDX contribute to its high parthenocarpy ability.