The CMS-based hybrid seed technology uses a three-line system that requires three different breeding lines: CMS line, maintainer line, and restore line (Figure 1). The CMS line has a male sterile cytoplasm with a gene causing CMS (hereinafter, CMS gene) and lacks a functional nuclear nuclear restorer of fertility and is used as the female parent. The maintainer line has a normal fertile cytoplasm, but contains the same nuclear genome as the CMS line and therefore serves as a male parent for the proliferation of the CMS line. The restore line has a functional Rf gene and therefore serves as the male parent to cross with the CMS line to produce F1 hybrid seeds. In F1 plants, the Rf gene restores male fertility, and the combination of nuclear genomes from the CMS line and the restorer line creates hybrid vigor.\cite{Chen_2014}