| Summary: | <p>Abstract</p> <p>Background</p> <p>The application of hybrid rice technology has significantly increased global rice production during the last three decades. Approximately 90% of the commercially cultivated rice hybrids have been derived through three-line breeding involving the use of WA-CMS lines. It is believed that during the 21<sup>st </sup>century, hybrid rice technology will make significant contributions to ensure global food security. This study examined the poorly understood molecular basis of the WA-CMS system in rice.</p> <p>Results</p> <p>RFLPs were detected for <it>atp6 </it>and <it>orfB </it>genes in sterile and fertile rice lines, with one copy of each in the mt-genome. The RNA profile was identical in both lines for <it>atp6</it>, but an additional longer <it>orfB </it>transcript was identified in sterile lines. 5' RACE analysis of the long <it>orfB </it>transcript revealed it was 370 bp longer than the normal transcript, with no indication it was chimeric when compared to the genomic DNA sequence. cDNA clones of the longer <it>orfB </it>transcript in sterile lines were sequenced and the transcript was determined unedited. Sterile lines were crossed with the restorer and maintainer lines, and fertile and sterile F<sub>1 </sub>hybrids were respectively generated. Both hybrids contained two types of <it>orfB </it>transcripts. However, the long transcript underwent editing in the fertile F<sub>1 </sub>hybrids and remained unedited in the sterile lines. Additionally, the editing of the 1.1 kb <it>orfB </it>transcript co-segregated with fertility restoring alleles in a segregating population of F<sub>2 </sub>progeny; and the presence of unedited long <it>orfB </it>transcripts was detected in the sterile plants from the F<sub>2 </sub>segregating population.</p> <p>Conclusion</p> <p>This study helped to assign plausible operative factors responsible for male-sterility in the WA cytoplasm of rice. A new point of departure to dissect the mechanisms governing the CMS-WA system in rice has been identified, which can be applied to further harness the opportunities afforded by hybrid vigor in rice.</p>
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