Comprehensive transcriptome analysis of AP2/ERFs in Osmanthus fragrans reveals the role of OfERF017-mediated organic acid metabolism pathway in flower senescence

<i>Osmanthus fragrans</i> is an ethylene-sensitive flower, and flower senescence was mediated by ethylene-responsive transcription factors (<i>OfERFs</i>). A total of 227 <i>OfERFs</i> were identified from <i>O. fragrans</i>, which were classified into five subfamilies: AP2 (35), DREB (57), ERF (125), RAV (6), and Soloist (4). Gene composition and structural analysis indicate that members of different subfamilies have different gene structures and conserved domains. Their gene promoter contains various functional responsive elements, including auxin, jasmonic acid, and other responsive elements. Among them, 124 <i>OfAP2/ERF</i> genes have expressed at any stage of flowering, and 10 of them may play roles in flowering or senescence. By comparative transcriptome analysis, <i>OfAP2/ERFs</i> affected by ethephon (ETH) and 5'-azacytidine (Aza) treatment were divided into three categories, which have various target gene sets. Importantly, these target gene sets participate in similar or different biological processes and metabolic pathways, suggesting that ethylene and DNA hypomethylation have crosstalk and a unique mechanism in regulating the flower senescence of <i>O. fragrans.</i> Co-expression analysis revealed that several key <i>OfAP2/ERFs</i> played a central role in organic acid metabolism and biosynthesis of branched-chain amino acids (BcAAs), among which <i>OfERF017</i> was selected for further functional analysis. Overexpression of <i>OfERF017</i> leads to significant enrichment of genes in organic acid metabolism pathways, which leads to a decrease in organic acid levels and promoting the flower senescence of <i>O. fragrans</i>. Together, these results give insights into the characteristics and functional analysis of <i>OfAP2/ERF</i> genes in <i>O. fragrans.</i>