T1243, an alternative transcript of the mitochondrial T gene in Brassica juncea var. tumida, causes pollen abortion in Arabidopsis thaliana

An earlier report revealed that the mitochondrial T gene of tumorous stem mustard (Brassica juncea var. tumida) is a cytoplasmic male sterility (CMS)-related gene. Two alternative transcripts of the T gene, T1170 and T1243, showed different expression patterns at different developmental stages. In this work, the potential roles of these two transcripts were studied in Arabidopsis thaliana through over-expression under the control of the cauliflower mosaic virus (CaMV) 35S promoter. Transgenic plants over-expressing the T1243 transcript produced anthers that appeared devoid of pollen and almost fully collapsed siliques, showing a severe male sterility phenotype, while transgenic lines over-expressing T1170 were normal. To confirm the above results, we constructed T1243-RNAi lines in A. thaliana, and T1243 was over-expressed using these lines as recipients. Pollen was normal in the T1243 knocked-out lines. In the control wild type lines expressing T1243, plants showed pollen abortion. We observed a positive correlation between the sterility phenotypes and the expression levels of T1243. Test-crossing was done by pollinating T1243 transgenic lines with wild type pollen. About half of the progeny showed pollen abortion, indicating that T1243, one of the T gene transcripts, can cause a male sterility phenotype.