Objective  The site-directed mutagenesis on grain-yield-related IPA1 to modifying the morphological characteristics of a rice plant for breeding purpose was studied.

  Method  Minghui 86, a rice elite restorer, was used in the study. The primary gene that governs the gain yield of the rice plant, IPA1, was edited using the transcription activator-like effector nucleases (TALENs) to generate mutated plants for subsequent identification by gene sequencing and cultivation on standard plots to verify results of the mutagenesis. Eight transgenic rice plants that differed in ipa1 sequences had the TALENs boxes cleaved for self-crossing followed by screening with PCR analysis to arrive at 4 mutants with 2bp, 4bp, 16bp or 23bp segment deleted in their IPA1 genes.

  Result  A phenotypic analysis on the 4 mutants free of exogenous transgenic elements confirmed that the site-directed mutagenesis on IPA1 had significantly altered the plant height, effective panicle number, panicle length, and grain number per panicle of the mutated rice plants. Compared with the wild-type Minghui 86, the plant height of the mutants was decreased by 7.9% to 11.4%, the effective panicle number increased by 46.9% to 68.4%, the panicle length shortened by 24.2% to 29.3%, the number of grains per panicle reduced by 31% to 34%, but the seed setting rate and 1000-grain weight were not changed significantly.

  Conclusion  The site-directed mutagenesis applying TALENs on IPA1 could significantly modify the plant height, effective panicle number, panicle length, and grain number per panicle on the new rice plant. The technique could be applied for the breeding program on rice to increase grain yield.