Transposable elements （TEs） are mobile genetic entities ubiquitously distributed in nearly all genomes. High frequency of codons ending in A/T in TEs has been previously observed in some species. In this study, the biases in nucleotide composition and codon usage of TE transposases and host nuclear genes were investigated in the AT-rich genome of Arabidopsis thaliana and the GC-rich genome of Oryza sativa. Codons ending in A/T are more frequently used by TEs compared with their host nuclear genes. A remarkable positive correlation between highly expressed nuclear genes and C/G-ending codons were detected in O. sativa （r=0.944 and 0.839, respectively, P〈0.0001） but not in A. thaliana, indicating a close association between the GC content and gene expression level in monocot species. In both species, TE codon usage biases are similar to that of weakly expressed genes. The expression and activity of TEs may be strictly controlled in plant genomes. Mutation bias and selection pressure have simultaneously acted on the TE evolution in A. thaliana and O. sativa. The consistently observed biases of nucleotide composition and codon usage of TEs may also provide a useful clue to accurately detect TE sequences in different species.
提出利用自然日长鉴定粳稻光敏不育系的方法。应用AMMI(additive main effects and multiplicative interaction)模型,对8个水稻光敏不育系对日长和温度反应的遗传敏感性进行比较分析,将其育性敏感期日长分成6个梯度,温度分成11个梯度。结果表明:在杭州自然条件下种植参试的8个不育系均为光敏核不育系,具有以下特性,抽穗前10～20d是育性转化敏感期,不育系的可育临界日长为13.0～13.8h,育性的临界高温为25.0℃,临界低温为21.0℃。
Pei＇ai64S, an indica sterile variety with photoperiod and thermo-sensitive genic male sterile （PTGMS） genes, has been widely exploited for commercial seed production for ＂two-line＂ hybrid rice in China. One PTGMS gene from Pei＇ai64S, pmsl（t）, was mapped by a strategy of bulked-extreme and recessive-class approach with simple sequence repeat （SSR） and insert and deletion （In-Del） markers. Using linkage analysis for the F2 mapping population consisting of 320 completely male sterile individuals derived from a cross between Pei＇ai64S and 93-11 （indica restorer） lines, the pmsl（t） gene was delimited to the region between the RM21242 （0.2 cM） and YF11 （0.2 cM） markers on the short arm of chromosome 7. The interval containing the pmsl（t） locus, which was co-segregated with RM6776, is a 101.1 kb region based on the Nipponbare rice genome. Fourteen predicted loci were found in this region by the Institute for Genomic Research （TIGR） Genomic Annotation. Based on the function of the locus LOC_Os07g12130 by bioinformatics analysis, it is predicted to encode a protein containing a Myb-like DNA-binding domain, and may process the transcript with thermosensory response. The reverse transcription-polymerase chain reaction （RT-PCR） results revealed that the mRNA levels of LOC_Os07g12130 were altered in different photoperiod and temperature treatments. Thus, the LOC_Os07g12130 locus is the most likely candidate gene for pmsl（t）. These results may facilitate not only using the molecular marker assisted selection of PTGMS genes, but also cloning of the pmsl（t） gene itself.
