Three types of maize male sterile lines. According to the website of People's Republic of China (PRC) and the Ministry of Agriculture, S-type cytoplasmic male sterility in maize is one of the three types of male sterile lines in maize, which can be used to create female sterile lines to produce maize hybrid seeds. It is caused by the specific expression of the sterile gene ORF355 encoded by mitochondria during microspore development, which can be regarded as a special mitochondrial variation.