Competitive network of polyamines metabolic and ethylene biosynthesis pathways during gibberellin-induced parthenocarpic grape fruit setting

Polyamines (PAs) and ethylene are involved in the modulation of plant growth and development. However, their roles in fruit-set, especially in exogenous gibberellin (GA₃)-induced grape parthenocarpic berries, and the related competitive action mode are poorly understood. For this, we, here performed their content determination, bioinformatics and expression pattern analysis of genes to identify the key ones in the competitive network of polyamines metabolic and ethylene biosynthesis (PMEB) pathways. The content of putrescine (Put) significantly increased; while 1-aminocyclopropanecarboxylic acid (ACC) sharply decreased during the fruit-set process of GA₃-induced grape parthenocarpic seedless berries. Totally, twenty-five genes in PMEB pathways, including 20 polyamines metabolic (PM) genes and 5 ethylene biosynthesis (EB) ones were identified in grape, of which 8 PM and 2 EB genes possessed the motifs responsive to phytohormone GA. The expression levels of most PMEB genes kept changing during grape fruit-set generating a competitive action mode of GA₃-mediated two metabolic fluxes toward PAs and ethylene synthesis. Exogenous GA₃ might enhance grape fruit-set of parthenocarpic berries via up-regulation of VvSAMS4, VvSAMDC1/2, VvODC1, VvSPDS1, and VvPAO1 to promote PAs accumulation, whereby repressing the ethylene synthesis by down-regulation of VvACS1 and VvACO2. Our findings provide novel insights into GA₃-mediated competitive inhibition of ethylene by PAs to promote the fruit-set of parthenocarpic berries in grape, which has important implications for molecular breeding of seedless grape with high fruit-setting rate.