Mitochondrially-targeted expression of a cytoplasmic male sterility-associated orf220 gene causes male sterility in Brassica juncea

Abstract

BackgroundThe novel chimeric open reading frame (orf) resulting from the rearrangement of a mitochondrial genome is generally thought to be a causal factor in the occurrence of cytoplasmic male sterility (CMS). Both positive and negative correlations have been found between CMS-associated orfs and the occurrence of CMS when CMS-associated orfs were expressed and targeted at mitochondria. Some orfs cause male sterility or semi-sterility, while some do not. Little is currently known about how mitochondrial factor regulates the expression of the nuclear genes involved in male sterility. The purpose of this study was to investigate the biological function of a candidate CMS-associated orf220 gene, newly isolated from cytoplasmic male-sterile stem mustard, and show how mitochondrial retrograde regulated nuclear gene expression is related to male sterility.ResultsIt was shown that the ORF220 protein can be guided to the mitochondria using the mitochondrial-targeting sequence of the β subunit of F1-ATPase (atp2-1). Transgenic stem mustard plants expressed the chimeric gene containing the orf220 gene and a mitochondrial-targeting sequence of the β subunit of F1-ATPase (atp2-1). Transgenic plants were male-sterile, most being unable to produce pollen while some could only produce non-vigorous pollen. The transgenic stem mustard plants also showed aberrant floral development identical to that observed in the CMS stem mustard phenotype. Results obtained from oligooarray analysis showed that some genes related to mitochondrial energy metabolism were down-regulated, indicating a weakening of mitochondrial function in transgenic stem mustard. Some genes related to pollen development were shown to be down-regulated in transgenic stem mustard and the expression of some transcription factor genes was also altered.ConclusionThe work presented furthers our understanding of how the mitochondrially-targeted expression of CMS-associated orf220 gene causes male sterility through retrograde regulation of nuclear gene expression in Brassica juncea.

Mitochondrial-targeted Expression of orf456 Causes Male Sterility in Chinese Cabbage (Brassica rapa L.)

“…2c-4, c-5). These phenotypes of aberrant floral organs in transgenic B. rapa are similar with others studies (Yang et al 2010 andKim et al 2007). …”

“…Furthermore, many genes related to the mitochondrial respiratory complex and pollen development were observed to be down-regulated in transgenic plants and the CMS lines (Yang et al 2010). To date, functional genes specifically related to pollen development have been well documented.…”

“…var. tumida Tsen et Lee) (Yang et al 2010). A chimeric gene orf220-atp2-1 was transformed into in wild-type stem mustard.…”

“…Mutation of any of these genes causes failure of microsporogenesis or abortion of pollen (He ea al. 1996;Kim et al 2007;Shi et al 2010;Yang et al 2010). We used three different approaches to estimate pollen viability: plasmolysis test, staining pollen with dyes and in vitro germination assay (Tuinstra and Wedel 2000).…”

Development of Molecular Markers and Application for Breeding in Chinese Cabbage

“…배추속 이외에 무속(Raphanus) 작물에서도 Ogura, Kosena 등이 알려져 있다 (Krishnasamy and Makaroff, 1993;Makaroff and Palmer, 1988) CMS 구별을 위한 마커로 배추과 작물(예, 갓)의 미토콘드 리아 유전체 중 atpA 유전자 근방의 orf220 및 nad2 유전자 근방의 orfB로부터 개발된 것이 보고되었다 (Yang et al, 2007). …”