Characterization of odor-contributing volatile in Capsicum chinense ‘JT-1’fruits during development and transcriptome analysis of key fruit-aroma formation periods

• Main odor-contributing volatile of fruity aroma in C. chinense pepper ‘JT-1’ is 4-Methylpentyl 3-methylbutanoate. • A shift in the dominant volatile organic compound (VOC) profile from aldehydes and alcohols to esters occurred from 3 to 4 WAF. • Transcriptome analysis of fruits at these two stages and qPCR results revealed that the up-regulating of CcBcat 4 may play an essential role in accumulating of 4-methylpentyl 3-methylbutanoate in chili pepper. Chili pepper ( Capsicum spp.) is one of the world's most popular vegetables and spices. C. chinense is a widely consumed domesticated pepper species. Most varieties of this species have distinctive fruity aromas, a trait with high commercial value. Studies have shown that branched-chain esters are the main contributors to the fruity aroma; however, the mechanisms of their accumulation and regulation remain elusive. In this work, we conducted gas chromatography–olfactometry–mass spectrometry analysis of C. chinense pepper ‘JT-1’ fruits harvested from 1 to 7 weeks after flowering (WAF). The main odor-contributing volatile of fruity aroma in ‘JT-1’ fruits was 4-methylpentyl 3-methylbutanoate, the concentration of which dramatically increased at 4 WAF. A shift in the dominant volatile organic compound (VOC) profile from aldehydes and alcohols to esters occurred from 3 to 4 WAF. Transcriptome analysis of fruits at these two stages and qPCR results revealed that the up-regulating of CcBcat 4 may play an essential role in accumulating of 4-methylpentyl 3-methylbutanoate in chili pepper. Our findings shed light on the molecular mechanism of aroma biosynthesis in pepper and provide a theoretical basis for the molecular breeding of high-quality pepper fruits.