Q63. Which of the following option(s) is/are CORRECT in the context of hybrid
plant generation using Barnase/Barstar–based male sterile lines?
(A) Barnase inhibits Barstar.
(B) Barstar inhibits Barnase.
(C) Barnase and Barstar are used to generate the male sterile line and the restorer
line, respectively.
(D) Barnase and Barstar are used to generate the restorer line and the male sterile
line, respectively.
Barnase/Barstar system induces male sterility in plants for hybrid seed production, where Barnase causes pollen abortion and Barstar restores fertility. Correct options are (B) and (C).
Option Analysis
Barnase, a ribonuclease from Bacillus amyloliquefaciens, degrades RNA in tapetum cells under tissue-specific promoters, leading to male sterility. Barstar specifically inhibits Barnase by binding tightly, preventing its RNase activity.
-
(A) Incorrect: Barnase does not inhibit Barstar; Barstar inhibits Barnase.
-
(B) Correct: Barstar inhibits Barnase, neutralizing its cytotoxic effect for fertility restoration.
-
(C) Correct: Barnase generates the male sterile (A) line; Barstar generates the restorer (R) line, used as male parent for fertile hybrids.
-
(D) Incorrect: Reverses the assignment; Barnase for sterile, Barstar for restorer.
Barnase/Barstar-based male sterile lines enable efficient hybrid plant generation by controlling pollen viability in crops like soybean, mustard, and canola. This biotechnology system revolutionizes breeding for hybrid vigor without manual emasculation.
System Mechanism
Barnase expresses in anther tapetum cells, destroying RNA and causing male sterility. Barstar, its specific inhibitor, binds Barnase with high affinity (Kd ~10^{-14} M), restoring fertility in F1 hybrids when pollen from Barstar lines fertilizes sterile plants.
Line Applications
-
Male sterile (A-line): Barnase under tapetum promoter (e.g., TA29) blocks pollen; maintained via linked herbicide resistance like bar.
-
Restorer (R-line): Barstar expression; higher dosage ensures fertility rescue.
-
Hybrid production: A-line × R-line yields fertile F1 seeds with heterosis.
This system supports CSIR NET topics in plant biotech, genetic engineering, and male sterility systems.
