Practice question

Barnase-Barstar system pioneered by Mariani 1990 represents engineered transgenic male sterility mimicking natural tapetal ablation. Barnase from Bacillus amyloliquefaciens encodes extracellular RNase that hydrolyzes single-stranded RNA causing cellular cytotoxicity when driven specifically in tapetum by TA29 promoter active in early anther development, leading to premature tapetal degradation, microspore starvation and complete sterility. Barstar from same bacterium encodes small protein forming stoichiometric complex blocking Barnase active site with high affinity, neutralizing toxicity. Restorer transgenic line expresses Barstar under same tapetum promoter, so when barnase sterile female crossed with barstar male, hybrid co-expresses inhibitor restoring fertility because Barstar binds Barnase in hybrid tapetum preventing RNA degradation. Only commercialized transgenic sterility method known as SeedLink used in mustard and rice under biosafety regulation enabling hybrid without natural CMS source. This understanding supports competitive exam preparation for NEET, GATE and CSIR NET concepts linking genotype with phenotype through molecular pathways involving transcription factors, hormones and metabolic enzymes that regulate development, adaptation and reproductive biology in applied breeding programs.