Abstract
During fruit ripening in Capsicum species, substantial amounts of carotenoids accumulate in the pericarp. While the carotenoid biosynthesis pathway in Capsicum species has been extensively investigated from various angles, the transcriptional regulation of genes encoding carotenoid biosynthetic enzymes remains less understood in this non-climacteric horticultural crop compared to tomato, a climacteric fruit. In the present study, we investigated the function of the NAM, ATAF1/2 or CUC2 81 (CaNAC81) transcription factor gene. This gene was selected through RNA-Seq co-expression analysis based on the correlation between expressed transcription factor gene profiles and those of carotenoid structural genes. To determine its role in regulating the expression of biosynthetic-related carotenogenic genes, we performed Virus-Induced Gene Silencing (VIGS) assays in the Serrano-type C. annuum 'Tampiqueño 74'. Fruits from plants infected with a pTRV2:CaNAC81 construct (silenced fruits) exhibited altered carotenoid pigmentation accumulation, manifested as yellow-orange spots, in contrast to fruits from non-agroinfected controls (NTC) and fruits from plants infected with the empty TRV2 construct (red fruits). Quantitative real-time PCR (qPCR) assays confirmed decreased transcript levels of CaNAC81 in fruits displaying altered pigmentation, along with reduced transcription of the PSY gene, which encodes the carotenoid biosynthetic enzyme phytoene synthase (PSY). High-performance liquid chromatography (HPLC) analysis revealed a distinct carotenoid pigment accumulation pattern in fruits from plants showing silencing symptoms, characterized by low concentrations of capsanthin and zeaxanthin and trace amounts of capsorubin, compared to control plants (NTC). These findings suggest the involvement of CaNAC81 in the regulatory network of the carotenoid biosynthetic pathway in chili pepper fruits.