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The stay-green trait is of considerable importance in extending the shelf life of green pepper fruit (Capsicum annuum L.) and in enhancing the appearance of ornamental plants. The study revealed the genetic and regulatory mechanisms of the stay-green trait in pepper, which will aid in the selection of ornamental pepper varieties. In this study, a pepper mutant with stay-green fruit named TNX348 was identified from a germplasm resource bank. Two segregating populations were constructed using the stay-green mutant TNX348 and then used in bulked segregant analysis combined with RNA sequencing and linkage analyses. The causal gene of the stay-green trait was mapped to an approximately 131-kb region, and a senescence-induced chloroplast protein gene, CaSGR1 (Capana01g000359), was identified as a candidate gene. Sequencing analysis revealed a G→A single-base mutation of CaSGR1 in TNX348 that led to early termination of translation. Based on the single-base mutation, a single nucleotide polymorphism (SNP) marker co-segregating with the stay-green trait was developed. Furthermore, in transcriptome analysis, expression patterns of 11 hormone transduction-related transcription factors, such as abscisic acid-insensitive (ABI), abscisic acid-responsive element-binding factor (ABF), and NAC transcription factor, were similar or opposite to that of CaSGR1. The results indicated that the transcription factors might mediate chlorophyll degradation by regulating the expression of CaSGR1.

The male-sterile line has been largely used in the hybrid seed production of pepper, which can effectively improve the efficiency of hybrid seed production. However, the formation mechanism of male sterility in pepper remains unclear. In the present study, we compared the gene expression patterns between pepper cytoplasmic male sterile line 9704A and its maintainer 9704B during floral bud development using RNA sequencing technology. A total of 547 976 and 2 416 Differentially Expressed Genes (DEGs) were identified in the stage S1, S2 and S3, respectively, and more than 70% of the DEGs were down-regulated in the sterile line. Gene Ontology (GO), and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were performed to further understand the functions of these identified DEGs. The results showed that the DEGs were mainly enriched in pathways of starch and sucrose metabolism, pentose and glucuronate interconversions. A number of genes, such as MS1, PME5, ATPB, and lots of transcription factors were found down-regulated in the sterile line, and we also identified a series of genes with large differences in expression patterns between sterile line and maintainer line. Collectively, our findings laid a foundation for further molecular breeding in pepper and provided new insights into its mechanism underlying the male sterility. Keywords: pepper, capsicum annuum, cytoplasmic male sterility, comparative transcriptome analysis, DEGs