An unedited 1.1 kb mitochondrial orfB gene transcript in the Wild Abortive Cytoplasmic Male Sterility (WA-CMS) system of Oryza sativa L. subsp. indica

Abstract

BackgroundThe 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 21st 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.ResultsRFLPs were detected for atp6 and orfB 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 atp6, but an additional longer orfB transcript was identified in sterile lines. 5' RACE analysis of the long orfB 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 orfB 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 F1 hybrids were respectively generated. Both hybrids contained two types of orfB transcripts. However, the long transcript underwent editing in the fertile F1 hybrids and remained unedited in the sterile lines. Additionally, the editing of the 1.1 kb orfB transcript co-segregated with fertility restoring alleles in a segregating population of F2 progeny; and the presence of unedited long orfB transcripts was detected in the sterile plants from the F2 segregating population.ConclusionThis 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.

A Comparative Analysis of the atp8 Gene Between a Cytoplasmic Male Sterile Line and Its Maintainer and Further Development of a Molecular Marker Specific to Male Sterile Cytoplasm in Kenaf (Hibiscus cannabinus L.)

“…S6). Sequence alignment showed that 9-bp insertion at 3′flanking region of atp8 in CMS line UG93A compared with its maintainer line UG93B, however, the transcripts of atp8 in UG93A, UG93B, and F 1 (UG93A/992) were the same, meanwhile the editing frequencies of atp8 were higher in sterile cytoplasm than in fertile cytoplasms, which were different from that of Wang et al (2009) and Das et al (2010), means that atp8 maybe not a direct cause of CMS in kenaf.…”

“…Yang et al (2009) showed that one novel open reading frame orfB gene which was located at the downstream of the mitochondrial nad2 gene and high similarity to atp8, was expressed specifically in a CMS line of Brassica juncea, pointing to a possibility that nad2 may be co-transcripted with CMS-associated orfB (atp8) gene in CMS stem mustard (Brassica juncea). Das et al (2010) identified another longer orfB (atp8) transcript in the rice (Oryza sativa L.) with WA-CMS line but absent in the fertile line. Complementary DNA (cDNA) analysis showed that the transcript was unedited in sterile line but cosegregated with fertility restoring alleles in a segregating population of F 2 progeny, indicating that the unedited atp8 gene transcript was specific to the WA-CMS system in rice.…”

A Reevaluation of Rice Mitochondrial Evolution Based on the Complete Sequence of Male-Fertile and Male-Sterile Mitochondrial Genomes

“…Recently, an unedited orfB transcript specific to the WA-CMS cytoplasm was identified as a putative candidate for inducing the male sterility phenotype (Das et al, 2010). However, it should be noted that this longer and unedited version of the orfB transcript represents only a small fraction of the pool of orfB transcripts found in the sterile lines; the remainder of the transcript is similar in size and editing status to the fertile lines.…”

Gene, protein, and network of male sterility in rice

“…The molecular mechanism of CMS-WA is poorly understood compared with that of CMS-HL and CMS-BT. Previously, an unedited 1.1 kb mitochondrial orfB gene transcript was found to be the candidate sterility gene of WA-CMS by RFLP (Das et al, 2010). But recently, Bentolila and Stefanov suggest orf126 is the CMS-related candidate gene based on comparison of mitochondrial genomes by next-gen sequencing (Bentolila and Stefanov, 2012).…”