Background: Cytoplasmic male sterility (CMS) and its restoration of fertility (Rf) system is an important mechanism to produce F₁ hybrid seeds. Understanding the interaction that controls restoration at a molecular level will benefit plant breeders. The CMS is caused by the interaction between mitochondrial and nuclear genes, with the CMS phenotype failing to produce functional anthers, pollen, or male gametes. Thus, understanding the complex processes of anther and pollen development is a prerequisite for understanding the CMS system. Currently it is accepted that the Rf gene in the nucleus restores the fertility of CMS, however the Rf gene has not been cloned. In this study, CMS line 8A and the Rf line R1, as well as a sterile pool (SP) of accessions and a restorer pool (RP) of accessions analyzed the differentially expressed genes (DEGs) between CMS and its fertility restorer using the conjunction of RNA sequencing and bulk segregation analysis. Results: A total of 2274 genes were up-regulated in R1 as compared to 8A, and 1490 genes were up-regulated in RP as compared to SP. There were 891 genes up-regulated in both restorer accessions, R1 and RP, as compared to both sterile accessions, 8A and SP. Through annotation and expression analysis of co-up-regulated expressed genes, eight genes related to fertility restoration were selected. These genes encode putative fructokinase, phosphatidylinositol 4-phosphate 5-kinase, pectate lyase, exopolygalacturonase, pectinesterase, cellulose synthase, fasciclin-like arabinogalactan protein and phosphoinositide phospholipase C. In addition, a phosphatidylinositol signaling system and an inositol phosphate metabolism related to the fertility restorer of CMS were ranked as the most likely pathway for affecting the restoration of fertility in pepper. Conclusions: Our study revealed that eight genes were related to the restoration of fertility, which provides new insight into understanding the molecular mechanism of fertility restoration of CMS in Capsicum.

A cytoplasmic male sterility (CMS) system is one of the most efficient ways to produce F ₁ hybrid seeds in pepper ( Capsicum annuum ). Restorer-of-fertility ( Rf ) genes are a critical component within the CMS/ Rf system. The inheritance of Rf genes in pepper by joint segregation analysis was examined. The inheritance of Rf genes in the two progenies was controlled by two major additive-dominant epistatic genes and additive-dominant epistasis polygene. The two major genes had high additive effects and dominant effects. In addition, there existed significant epistatic effects between the two major genes. The major genes had high heritability in F ₂ , BC ₁ , and BC ₂ generations. Also, the fertility restorer characteristic can be selected during early generations of the breeding cycle.

Trehalose, as a non-reductive disaccharide, plays a vital role in plant growth and development and resistance to abiotic stress. Trehalose-6-phosphate synthase (TPS) is a key enzyme in the synthesis mechanism of trehalose and TPS1 genes play a crucial role in the response to abiotic stress in plants. However, it has rarely been reported that CaTPS1 responds to cold and salt stresses in pepper. To verify the function of CaTPS1 in response to cold and salt stresses, CaTPS1 was silenced by virus-induced gene silencing (VIGS). Subsequently, the expressions of CaTPS1, plant morphology and some physiological indexes were analyzed after cold and salt stresses in pepper. The results showed that the expression of CaTPS1 was significantly lower in CaTPS1-silenced (pTRV2-CaTPS1) plant than that in the non-VIGS (CK) and negative control (PTRV2-00) plants. The parameters of response to cold and salt stresses have changed accordingly. The chlorophyll content decreased, while the trehalose content, peroxidase (POD) activity, catalase (CAT) activity and ascorbate peroxidase (APX) activity increased in all treatments. However, these parameters of response to cold and salt stresses were significantly lower in pTRV2-CaTPS1 plant than in CK and PTRV2-00 plants. This study suggested that CaTPS1 was involved in the response to cold and salt stresses in pepper.