2018 ASHS Annual Conference

Hydrogen cyanamide (HC) is used in deciduous fruit trees to induce bud endo-dormancy release and to offset insufficient chilling hours for bud break. The objective of this study was to gain insight into the mechanism of bud break response to HC in 'TropicBeauty' peach trees (Prunus persica L.) by comparing buds from HC-treated and non-HC-treated control trees, respectively, at the global transcriptomic level using RNA sequencing. For HC-treated trees, the peak of bud burst (7 flower buds and 10 vegetative buds/branch) occurred at 32 days after treatment (DAT). In contrast, control trees had maximum release of bud dormancy (10 flower and 14 vegetative buds/branch) at 74 DAT, six weeks later than treated with HC, suggesting HC accelerated bud break in peach. Between HC-treated and control trees, there were 1312 and 1095 deferentially expressed genes (DEGs) at 3 and 7 DAT, respectively. The results of gene ontology (GO) enrichment analysis demonstrated that at 3 DAT, significant GO terms with top enrichment values (EV; absolute logarithm of P-value) for up-regulated DEGs included response to stimulus (EV = 18.1), response to stress (EV = 15.7), oxidoreductase activity (EV = 14.6), and oxidation reduction (EV = 10.7), whereas top GO terms for down-regulated DEGs were cell proliferation (EV = 8.0), regulation of multicellular organismal process (EV = 7.1), chromosome organization (EV = 6.7), and anatomical structure development (EV = 6.1). Interestingly, at 7 DAT, top GO terms for up-regulated DEGs shifted to cell cycle (EV = 9.7), chromosome organization (EV = 9.5), chromatin organization (EV = 8.7), and cell cycle process (EV = 8.7), indicating resumption and increase in cell division and growth following the initial suppression by HC treatment. For down-regulated DEGs at 7 DAT, top GO terms included response to stimulus (EV = 6.9), response to chemical stimulus (EV = 6.2), and response to stress (EV = 3.6). The results suggest HC induces oxidative stress in buds shortly after application leading to the release of bud dormancy and subsequently causes increased cell activity, resulting in floral and vegetative bud break.