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Tree peony ( Paeonia rockii ) is an excellent woody oilseed crop, known for its high α-linolenic acid (ALA, ~45%) content, which is of great value for human health. However, the mechanisms underlying this high-level ALA accumulation in tree peony seeds are poorly understood. In this study, we evaluated the dynamic changes in the lipidomic profile of P. rockii seeds during development. A total of 760 lipid molecules were identified in P. rockii seeds; triacylglycerol (TAG) lipid molecules showed the highest abundance and diversity, both increasing during seed development. Particularly, ALA was the predominant fatty acid at the TAG sn -3 position. We further characterized two diacylglycerol acyltransferase (DGAT) genes and three phospholipid:diacylglycerol acyltransferase (PDAT) genes involved in the transfer of fatty acids to the TAG sn -3 position. Gene expression and subcellular localization analyses suggested that PrDGATs and PrPDATs may function as endoplasmic reticulum-localized proteins in seed TAG biosynthesis. In vitro functional complementation analysis showed different substrate specificities, with PrPDAT2 having a specific preference for ALA. Multiple biological assays demonstrated that PrDGAT1, PrDGAT2, PrPDAT1-2, and PrPDAT2 promote oil synthesis. Specifically, PrPDAT2 leads to preferential ALA in the oil. Our findings provide novel functional evidence of the roles of PrDGAT1 and PrPDAT2 , which are potential targets for increasing the ALA yield in tree peony and other oilseed crops., Competing Interests: None declared., (© The Author(s) 2023. Published by Oxford University Press on behalf of Nanjing Agricultural University.)

Flower senescence is commonly enhanced by the endogenous hormone ethylene and suppressed by the gibberellins (GAs) in plants. However, the detailed mechanisms for the antagonism of these hormones during flower senescence remain elusive. In this study, we characterized one up-regulated gene PhOBF1 , belonging to the basic leucine zipper transcription factor family, in senescing petals of petunia ( Petunia hybrida ). Exogenous treatments with ethylene and GA 3 provoked a dramatic increase in PhOBF1 transcripts. Compared with wild-type plants, PhOBF1 -RNAi transgenic petunia plants exhibited shortened flower longevity, while overexpression of PhOBF1 resulted in delayed flower senescence . Transcript abundances of two senescence-related genes PhSAG12 and PhSAG29 were higher in PhOBF1 -silenced plants but lower in PhOBF1 -overexpressing plants. Silencing and overexpression of PhOBF1 affected expression levels of a few genes involved in the GA biosynthesis and signaling pathways, as well as accumulation levels of bioactive GAs GA 1 and GA 3 . Application of GA 3 restored the accelerated petal senescence to normal levels in PhOBF1 -RNAi transgenic petunia lines, and reduced ethylene release and transcription of three ethylene biosynthetic genes PhACO1 , PhACS1 , and PhACS2 . Moreover, PhOBF1 was observed to specifically bind to the PhGA20ox3 promoter containing a G-box motif. Transient silencing of PhGA20ox3 in petunia plants through tobacco rattle virus-based virus-induced gene silencing method led to accelerated corolla senescence. Our results suggest that PhOBF1 functions as a negative regulator of ethylene-mediated flower senescence by modulating the GA production., Competing Interests: The authors declare that they have no conflict of interest., (© The Author(s) 2023. Published by Oxford University Press on behalf of Nanjing Agricultural University.)