Tapetum specific expression of unedited nad3 gene from safflower and targeting the protein into mitochondria induces male sterility in transgenic tobacco plants

The ability of NAD3 (subunit 3 of the NADH ubiquinone oxidoreductase) encoded by unedited nad3 (u-nad3) gene, when targeted into mitochondria, to cause ablation of tapetum was investigated. A gene construct was developed by cloning the coxIV presequence from yeast and the u-nad3 from safflower under the tapetum specific TA29 promoter to target U-NAD3 into mitochondria in the tapetal cell layer. Transgenic tobacco plants were realized with this construct using the Agrobacterium mediated transformation method and confirmed for the presence of the transgene. Among these plants, three were completely sterile and four were semi-sterile. The male sterile plants were morphologically similar to fertile plants, but the anthers were shorter and remained regressed below the stigma surface at anthesis. RT-PCR and western blotting confirmed anther specific expression of u-nad3 in these plants. Stable inheritance of the induced male sterility and its co-segregation with the introduced gene cassette was confirmed in the test cross progeny. This study demonstrates the proof-of-concept that u-nad3 could be used as a candidate to induce transgenic male sterility in plants.