Analyisis Of Two Complete Mitochondrial Genome Of Rice Stem Borers

Sesamia inferens (Walker), Chilo suppressalis (Walker), Tryporyza incertulas (Walker) and Chilo auricilius Dugeon are all well-known rice pests that are widely distributed in the main rice-growing regions of China. In recent decades, due to the expansion of hybrid rice cultivation and changes in climate and rice cropping systems, these species have been gradually increasing in several regions of China, causing the most serious damage. In the paper, we sequence and analyze of the mitochondrial genomes of T. incertulas and C. auricilius, and analyze of the resemblances and differences of the four stem borers. At the same time, we compared the mitochondrial genomes of eight Pyraloidea moths. The results were follows:1. The mitogenome of T. incertulas was a circular molecule consisting of 15,223 nucleotides and contains 37 genes including 13 protein-coding genes (PCGs),22 tRNA genes, two rRNA genes and a large non-coding region. The 12 PCGs initiated with ATN as the start codon except coxl, and terminated with TAA, TA or T as stop codon except nad3 using TAG. Among the 22 tRNA genes, only trnSer(AGN) did not have the typical clover-leaf structure due to the lack of the DHU arm. The secondary structure of rrnL consisted of five domains (labeled Ⅰ, Ⅱ, Ⅳ, Ⅴ and Ⅵ) with 49 helices. Each domain was separated by a single-stranded region, and domain Ⅲ was absent in arthropod mitogenomes. And the rrnS consisted of three structural domains and 33 helices. Finally, the A+T-rich region contained two potential stem-loop structures, a duplicated 19-bp repeat element, and two microsatellites ’(TA)12’ and ’(TA)9’ were observed in the A+T-rich region of T. incertulas mitogenome.2. The mitogenome of Chilo auricilius was 15,367 bp long excluding the control region, including 37 typical genes that similar to T. incertulas mitogenome. Besides trnSer (AGN) lacked for dihydrouridine arm, other tRNAs had typical secondary structures of clover leaf. Secondary structure modeling of rRNA genes revealed similarity to other Lepidoptera insects. In addition, the A+T-rich region of mitochondrial genome have evolved to have five alternative flanking sequence forms, two microsatellites ’(AT)6’,’(TA)11’, a duplicated 12-bp repeat element, and a 27-bp repeat element were detected in C. auricilius.3. The intergenic spacer 2 (INGS2), located between trnY and cox1 harbors a motif (TnATnG) in Crambidae moths, but S. inferens had a motif of TAG. Along with the intergenic spacer 4 (INGS4), there was a conserved motif’ATACTAAA’ between trnS2 (UCN) and nad1 in Crambidae moths. And there is no micro satellite in C. suppressalis, a stem- and-loop structure in S. inferens, but not in C. suppressalis or C. auricilius. All the contents of A were higher than those of T excluding C. cephalonica and C. medinalis. Five genes, trnN, trnl, trnL, trnF, and trnS, were the most abundant in eight Pyraloidea moths which were two-fold degenerate in codon usage. The intergenic spacer located between trnQ and nad2, the overlapping sequence located between atp8 and atp6 were common in Lepidoptera species. Along with the intergenic spacer 4 (INGS4), there was a 6 bp motif ’ATACTA’ between the trnS2(UCN) and nadl in Pyraloidea moths.