Characterization and inheritance of a novel thermo-sensitive restoration of cytoplasmic male sterility in Capsicum annuum

• Male sterility of a novel thermo-sensitive cytoplasmic male-sterile pepper that is restored at low temperature below 13 °C was found.
• Pollen development of fertile and sterile thermo-sensitive cytoplasmic male-sterile (TCMS) lines was compared.
• Callose wall deposition at the tetrad stage was failed in the thermo-sensitive male-sterile plants.
• Less subcellular organelles were identified in tapetal cells of thermo-sensitive male-sterile lines than in thermo-sensitive fertile lines.
• The thermo-sensitive restorer gene may be another allele of Rf locus and is recessive to Rf and dominant to rf.

Thermo-sensitive male sterility can be used for two-line hybrid production, if the fertility can be manipulated by temperature shifting. In this study, we investigated a novel thermo-sensitive cytoplasmic male-sterile (TCMS) line of pepper. The TCMS line was sterile at temperatures above 15 °C but their fertility was restored when night temperatures were below 13 °C. To elucidate the cellular mechanism acting in the TCMS line, histological analysis was performed using light microscopy and transmission electron microscopy (TEM). We demonstrated that stable male sterility in pepper might be induced due to the abnormal development of tapetal cells whereas defects of callose wall biosynthesis seemed to be the main reason for male sterility in TCMS plants. Meiotic cell division in sterile TCMS plants proceeded to the last stage, whereas normal sterile plants were arrested at the meiotic stage. Further analysis using TEM revealed that abnormal development and failure of timely programmed cell death of the tapetum led to secretory dysfunction of tapetal cells. Consequently, this secretory defect may have influenced callose wall deposition and pollen wall formation in sterile TCMS. To reveal genetic mechanisms influencing TCMS, inheritance and marker analysis was performed. Cytoplasmic male sterility (CMS)-associated marker tests showed that the TCMS line contains CMS cytoplasm. Inheritance patterns and Rf-linked marker analysis suggested that TCMS is controlled by an allele named RfTCMS located at the Rf locus. Restoring experiment at low temperature showed that the thermo-sensitive restorer, RfTCMS, may be another allele located on the Rf locus and is recessive to Rf and dominant to rf.