Employing male sterility to breed advantageous hybrids is the most economical and efficient approach. To date, two types of recessive nuclear male sterility resources for sweet peppers have been discovered in China; one is the pepper male sterile material discovered by Shizhou Yang with the nuclear sterility gene named msc1, and the other is the sweet pepper male sterile line AB91 used in this study with its nuclear sterility gene named msc2. To date, sweet pepper nuclear male sterile line AB91 has been used to breed five national recognized vegetable varieties (JiYan5, JiYan6, JiYan15, JiYan16, JiYan108) and nine provincial recognized vegetable varieties (JiYan8, JiYan12, JiYan13, JiYan19, JiYan4, JiYan105, JiYan102, JiYan20, JiYan28), which are widely planted throughout China.Therefore, it is of great meaning to study the sterility gene msc2 of the sweet pepper male sterile line AB91. However, the research on the infertility mechanism of the msc2 gene has not been reported yet. Whole genome sequencing technology (WGS) is currently the most effective method for group function genetic mining and has many advantages such as its ability to contain comprehensive, efficient, and accurate information. WGS is a bioinformatics technique that performs differential sequence analysis of individuals or groups at the genomic level to explore species and filter out functional genes[27]. Currently, WGS has been widely used in rice[28], cucumber[29], potato[30], watermelon[31], sorghum[32], and other crops. Therefore, this study carried out in-depth research to analyze the reason for abortion caused by gene msc2 using genetic sequencing and genotyping technology.
Material with prominent and genetically stable objective traits
The sweet pepper male sterile dual-purpose line AB91 is a sister cross-hybrid whose agronomic traits within groups have remained stable after years of breeding and whose sterility is controlled by a pair of recessive nuclear genes. The pure dominant fertile plant has a genetic background that is consistent with that of the pure recessive sterile plant, which avoids the wrong interference analysis caused by the genetic background difference between fertility materials.
Capana05g000747 is an important candidate gene of Msc2
In this study, the the mutation site that caused the abortion of sweet pepper male sterile AB91, which is on chromosome #5, was first discovered through WGS technology. Flight mass spectrometry genotyping was used to verify the differential gene and filter out the gene Capana05g000747, which is most likely to be the important gene leading to the abortion of sweet pepper male sterile AB91. For the gene Capana05g000747 including eight exons and seven introns, the mutation site 28549037 is a non-synonymous mutation site with its position at the 6th exon of Capana05g000747; the features with base C mutated into A and the amino acid changed from alanine to serine are what causes the male sterility of sweet pepper malesterile line AB91.
Sequence analysis of the Capana05g000747 gene
For a further function of the gene Capana05g000747, we performed a sequence alignment analysis that showed that the gene homology is close to tomato, potato, and tobacco, but their functional annotations were all predicted and are similar to that of the gene At2g02148. At2g02148 encodes a PPR gene protein, which is encoded by a nuclear gene and consists of 35 degenerate amino acids in a series of repeating units; most of the protein is transported into organelles to fulfill their functions [33]. The PPR gene protein has important physiological functions in the gene performance process of organelles and is involved in almost all stages of gene performance, including transcription[34], RNA splicing[35],RNA editing[36],translation[37], and RNA stability maintenance[38].Previous studies have shown that the PPR gene protein is dispersed all over the entire pepper genome[39-40], while most of the Rf candidate genes are on chromosome #6[41-42] and the sterility performance is realized by controlling the male sterility related genes. However, our research shows that the candidate gene protein PPR of the nuclear male sterility line AB91 on chromosome #5 has a base mutation, which causes a protein function change, resulting in abortion microspores, but the molecular mechanism of the PPR gene protein in the sweet pepper nuclear male sterility AB91 is still unclear and its verification will require further research.