Coexpression network analysis reveals an MYB transcriptional activator involved in capsaicinoid biosynthesis in hot peppers

Plant biosynthesis involves numerous specialized metabolites with diverse chemical natures and biological activities.The biosynthesis of metabolites often exclusively occurs in response to tissue-specific combinatorial developmental cues that are controlled at the transcriptional level.Capsaicinoids are a group of specialized metabolites that confer a pungent flavor to pepper fruits.Capsaicinoid biosynthesis occurs in the fruit placenta and combines its developmental cues.Although the capsaicinoid biosynthetic pathway has been largely characterized,the regulatory mechanisms that control capsaicinoid metabolism have not been fully elucidated.In this study,we combined fruit placenta transcriptome data with weighted gene coexpression network analysis(WGCNA)to generate coexpression networks.A capsaicinoid-related gene module was identified in which the MYB transcription factor CaMYB48 plays a critical role in regulating capsaicinoid in pepper.Capsaicinoid biosynthetic gene(CBG)and CaMYB48 expression primarily occurs in the placenta and is consistent with capsaicinoid biosynthesis.CaMYB48 encodes a nucleus-localized protein that primarily functions as a transcriptional activator through its C-terminal activation motif.CaMYB48 regulates capsaicinoid biosynthesis by directly regulating the expression of CBGs,including AT3a and KasIa.Taken together,the results of this study indicate ways to generate robust networks optimized for the mining of CBG-related regulators,establishing a foundation for future research elucidating capsaicinoid regulation.

Identification and Characterization of a LEA-like Gene, CaMF5,Specifically Expressed in the Anthers of Male-fertile Capsicum annuum

To improve the understanding of molecular mechanisms of anther and/or pollen development in Chili pepper, in the present study, fulllength cDNA and DNA sequences of the pollen development-related gene CaMF5 were obtained from the anthers of a Capsicum annuum nuclear male-fertile line. Sequence analysis indicated that the full length of CaMF5 was 747 bp, containing a maximum opening reading frame of 447 bp.Amino acid sequence alignment and phylogenetic analysis revealed that CaMF5 shared approximately 37%–77% homology with a series of uncharacterized or hypothetical proteins and late embryogenesis abundant(LEA) proteins from other plants. However, no LEA structural domain was detected in CaMF5, which indicated that it might be a new type of LEA gene. CaMF5 was only expressed in flower buds at stages 7 and 8 and in open flowers of the male-fertile line, whereas it exhibited no expression in any examined organs of the male-sterile line. In addition, CaMF5 showed the highest transcript abundance in the anthers of the male-fertile line, with no expression being detected in any other examined organs, such as the sepals, petals, pistils, roots, stems, or leaves. Taken together, our results suggest that CaMF5 is an anther-specific gene that might encode a new type of LEA protein related to anther and/or pollen development in C. annuum.