Study On The Fertility-restoration Mechanism Of S Type Cytoplasmic Male-sterility In Maize

Cytoplasmic male-sterility (CMS) is a common phenomenon in the flowering plants. This kind of sterility, caused by mutations in the mitochondrial genome (mt-genome), can usually be suppressed by the nuclear restorer genes, in which way the pollen fertility is restored. This study focused on the mRNA decay process of the transcripts of the candidate sterile gene in maize (Zea mays L.) CMS-S mitochondria under the action of nuclear restorer gene, and discussed about the biological mechanism of the fertility restoration.There are three main CMS types in maize: T, C and S. The S type of CMS (CMS-S) is a gametic sterility type, and its pollen sterility was considered to be associated with the expression of R region in the mitochondria. There are three copies of R fragment in the S mt-genome, and each copy contains two closely adjacent open reading frames (orf): orf355 and orf77. Among these three copies two BamHI fragments were cloned, and the sequence analysis showed that cox1 and cox2 gene lies upstream of the R region in each fragment, respectively. However, they locate in different strands and head to head with R. In this study, we found that:(1) The expression of cox1 and cox2 is not affected by the transcription of R region;(2) The two copies of R region transcribe in large amount in the microspores, and produce transcripts of 1.6kb and 2.8kb, respectively, in the sterile microspores; However, the abundance of these two transcripts is reduced in the fertility restored microspores, realized through the mRNA decay, and this reduction occurs at the uninucleate microspore stage;(3) In the sterile microspores, the 5' terminus of the 1.6kb transcript contains a palindrome region that can fold into a stem-loop. However, the 5' terminus is shortened by 9nt in the fertility restored microspores;(4) In both the sterile and restored microslores, the polyadenylation loci of the 1.6kb...