Association of A/T rich microsatellites with responses to artificial selection for larval developmental duration in the silkworm Bombyx mori

作者：Pradeep Appukuttan Nair Retnabhavan^*; Awasthi Arvind Kumar; Urs Raje Siddaraje

来源：Molecules and Cells, 2008, 25(4): 467-478.

• allele segregation in F-2
• AT rich microsatellites
• Bombyx mori
• larval duration
• loci-trait association
• selection

Simple sequence repeats (SSRs) and interSSR (ISSR) marker systems were used in this study to reveal genetic changes induced by artificial selection for short/long larval duration in the tropical strain Nistari of the silkworm Bombyx mori. Artificial selection separated longer larval duration (LLD) (29.428 +/- 0.723 days) and shorter larval duration (SLD) (22.573 +/- 0.839 days) lines from a base, inbred population of Nistari (larval span of 23.143 +/- 0.35 days). SSR polymorphism was observed between the LLD and SLD lines at one microsatellite locus, Bmsat106 (CAO and at two loci of 1074 bp and 823 bp generated with the ISSR primer UBC873. Each of these loci was present only in the LLD line. The loci segregated in the third generation of selection and were fixed in opposite directions. In the F-2 generation of the LLD x SLD lines, the alleles of Binsat106 and UBC873(1074bp) segregated in a 1:1 ratio and the loci were present only in the LLD individuals. UBC873(823bp) was homozygous. Single factor ANOVA showed a significant association between the segregating loci and longer larval duration. Together, the two alleles contributed to an 18% increase in larval duration. The nucleotide sequences of the UBCS73(1074bp) and UBC873(823bp) loci had 67% A/T content and consisted of direct, reverse, complementary and palindromic repeats. The repeats appeared to be "nested" (59%) in larger repeats or as clustered elements adjacent to other repeats. Of 203 microsatellites identified, dinucleotides (67.8%) predominated and were rich in A/T and T/A motifs. The sequences of the. (E UBC873(1074bp) and UBC873(823bp) loci showed similarity = 0.0) to contigs located in Scaffold 010774 and Scaffold 000139, respectively, of the B. mori genome. BLASTN analysis of the UBC873(1074bp) sequence showed significant homology of (nt.) 45-122 with upstream region of three exons from Bombyx. The complete sequence of this locus showed similar to 49% nucleotide conservation with transposon 412 of Drosophila melanogaster and the Ikirara insertions of Anopheles gambiae. The A + T richness and lack of coding potential of these small loci, and their absence in the SLD line, reflect the active process of genetic change associated with the switch to short larval duration as an adaptation to the tropics.

• 出版日期2008-6-30