Abstract:

It is well accepted that S type of cytoplasmic male sterility (CMS) in maize (Zea mays L.) is associated with R region in mitochondrial genome. R region includes two open reading frames — orf355 and orf77 and it is speculated that orf77 is an important candidate gene of CMS. RT-PCR showed that both DNA strands of R region are transcribed. Nuclear background or developing stages of plant do not influence the transcription of R region in the strand which also acts as template strand of coxⅠ/coxⅡ locating just upstream of R region, but they do influence the transcription of R region in the other strand (template strand of orf355-orf77). In tassel with nuclear background of rf3rf3, transcription of the template strand of orf355-orf77 is different from that in etiolated shoots with nuclear background of Rf3- or rf3rf3 and tassel with nuclear background of Rf3-. Compared to the same other three, it is truncated at about 238 base from the 5'' end of R region. Rabbit antiserum against putative ORF77 expressed in Escherichia coli was prepared but Western blot did not detect ORF77 in plant materials. It seems that double-strand transcription of R region inhibits the translation of orf77 and the transcribing mode of R region may be associated with male sterility.

Key words: maize, S type of CMS, mitochondrial DNA, R region, double-strand transcription