| Cytoplasmic male sterility (CMS) system, abortion of pollen grains but normal of eggs, is controlled by interactions of the cytoplasm and nuclear genes. The sterility inducing factor (S) in cytoplasm combining with the homozygotic recessive nuclear genes of fertile restore (rfrf) makes plants male sterile. Because CMS has an important economic relevance for the generation of hybrid and offers an attractive opportunity for exploring the mechanism how the nuclear genes regulate mitochondrial genes in multicellular organisms, it has received considerable attention during the past years both from breeders and biologists.Now lots of studies indicate cytoplasmic DNA is associated with CMS, and many CMS-related DNA fragments from mtDNA and cpDNA have been obtained and sequenced. But most of them from different plant species have not shown any degree of sequence similarity to each other. Even in cases where more than one type of CMS is found in a species, the DNA fragments possibly involved in conferring the trait appear to be unrelated. This means the hypothesis about the mechanism of CMS from one case does not fit for another. Obviously, identifying common gene(s)-associated with CMS from different plant species or CMS types is very necessary.With this purpose in mind, 15 sorghum materials, including 3 types of CMS cytoplasm A1, A2 and A3 and corresponding maintainer lines, restorer lines and F1 hybrids, were chosen. Among them, there are complicated maintaining-restoring relationships.Total DNAs of the 15 sorghum materials were supplied to RAPD analysis, and three special fragments, SAP-06950, SAY-192300, SAAU-027oo were obtained.SAP-06950 was unique to all CMS lines and its F1 hybrids, and the others were unique to all maintainer lines and restorer lines. These results revealed the tight linkage between SAP-06950 and male-sterile cytoplasm, and between SAAU-02700, SAY-192300 and male-fertile cytoplasm, which implied that the three fragments might be related to CMS of sorghum. Sequence alignment of SAAU-02700 and SAY-192300 showed strong homologies with ndhD, psaC gene and pslA1, pslA2 gene, respectively, so the partial sequences of ndhD, psaC gene and pslAl, pslA2 gene of chloroplast of sorghum were obtained. Sequence analysis of SAP-06950 revealed the presence of an open reading frame encoding 223 amino acids, and it was a new sequence.In order to determine the origins of the three fragments, the RAPD fingerprint patterns of mtDNA and cpDNA of A1Tx623 A/B and A2V4 A/B were performed. The results showed SAP-06950 was amplified from mtDNA of both CMS lines and cpDNA of A2V4, SAAU-02700 and SAY-192300 were amplified from cpDNA of both maintainer lines. The origins of the three fragments were further confirmed by Southern hybridization with total DNA, mtDNA and cpDNA of A1Tx623 A/B Jinliang 5, Kangsi, A2V4 A/B, 1383-2 and Jinza 12. SAP-06950 resulted in a hybridization pattern suggested its repetitive presence in mtDNA of all sorghums, and one hybridization band (950bps in size) which was unique to both the two CMS lines and their hybrids. SAAU-02700 and SAY-192300 were shown to hybridize specifically to cpDNA of all sorghums, but the restriction fragment hybridized showed length polymorphism among the CMS, maintainer, restorer lines and its hybrids. So the origin of SAP-06950 was mtDNA, SAAU-02700 and SAY-192300 were cpDNA.Some of different fragments appeared in the amplification of total DNA didn't occur in that of mtDNA and cpDNA from CMS line and its maintainer. What's wrong about it? We mean where those fragments are amplified from, cytoplasmic or nuclear DNA? The nuclei of CMS line and its maintainer line, in the opinion of genetics and reproductive biology, are identical, but the cytoplasmic DNA is different only, so we can conjecture any of the different fragments amplified from total DNA should be amplified also from mtDNA or cpDNA.To investigate the real origin of the different fragments, 184 random sequence 10 mer primers were used to screen the total DNA of cytoplasmic male... |
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