Three Grasshopper Mitochondrial Genome Sequencing And The Orthoptera Mitochondrial Genome Analysis

The complete mitogenome of Acrida cinerea, Filchnerella yongdengensis and Locusta migratoria manilensis which belong to superfamily Acridoidea of Orthoptera were determined and compared with that of other 55 orthoperans which determined by our research group and recorded in NCBI. The universal secondary structure of the mitochondrial 22 tRNA and 2 rRNA were predicted based on these mitochondrial genomes. Conclusions were showed below:(1)The length of the complete mitochondrial of L. m. manilensis, A. cinerea and F. yongdengensis are 15,895bp,15,599bp and 15,674bp respectively. They all display a typical gene composition found in insect mitogenomes:13 PCGs,22 tRNA genes,2 rRNA genes and an A+T-rich region. The gene arrangement of these three grasshoppers' mitogenomes is identical to those of other recorded sequences from Caelifera, which different from the ensiferans in the translocation from trnK-trnD to trnD-trnK. This arrangement of mitogenome may be the unique characteristic of caeliferans.(2)The typical initiation codon ATN not occurred in the mitogenomes of A. cinerea and F. yongdengensis. All the three mitogenomes have incomplete termination codon (T/TA) especially for nad5. The usage of synonymous codon markedly correlated with the nucleotide composition at third codon position, and not the anticodon of tRNA. Generally, the usage of codon that is A/T at the third codon position is higher than G/C.(3)The mismatches exist in secondary structure of the A.cinerea, F. yongdengensis and L. m. manilensis, mainly for wobble pair G-U. The tRNAs encoded by the J-strand generally contain more conservation sites than those encoded by the N-strand. The conservation of tRNA genes was not associated with the frequency of codon usage and A+T content. The model of secondary structure of 12S rRNA and 16S rRNA were predicted by comparative approach.(4)The average length of analyzed mtDNAs set is 15684±265bp, ranging from 14,971bp of R. dubia to 17,004bp of P. variolosa. The average length of PCGs is 11154±37bp, that the average codon usage number is 3718±12. The average length of 22 tRNAs gene,2 rRNAs and the A+T-rich region are 1447±7bp,2098±14bp and 835±278bp, respectively.(5)The average A+T% value for the analyzed mtDNAs set is 73.42%±2.45. In Orthoptera, the A+T contents of ensiferans are lower than those of caeliferan but have higher difference among the species, especially in the regions which have high A+Tcontent. Nevertheless, the second position of PCGs (average 65.59%) has the relative constant A+T concentration than other regions, whereas the A+T-rich (average 80.9%) and the third position of PCGs (84.8%) are highest.(6)A11 tRNAs from 58 orthopterans have the typical clover leaf structure except for trnS (agn) The tRNAs encoded by the H-strand generally contain more conservation sites than those encoded by the L-strand. The conservation of tRNA genes was not associated with the frequency of codon usage and A+T content.(7)The secondary structure and conserved consensus sequence of the 58 orthopterans rrnS is presented in this paper. It consists of 28 helices and subdivided into four principal domains (labeledⅠ,Ⅱ,Ⅲ, andⅣ), similar to the secondary structure of small ribosomal RNA subunits in prokaryotes.(8)The rrnL of orthopterans is divided into six domains (labeledⅠ,Ⅱ,Ⅲ,Ⅳ,ⅤandⅥ), each separated by a single stranded region. DomainⅢis absent in arthropods mitochondrion. Compared to the E.coli model, considerable degeneration in domainⅠof Orthoptera leads to only five remaining helices.(9)A stem-loop structure,16 bp or longer, also exists in the same position in all of the taxa from Caelifera, Gryllidae and Gryllotalpidae. Furthermore, at the basal three couplets was well established by CCSs and conserved in other pairs of the stem-loop structure. The flanking regions, including "TATA" on the 5'end and "G (A)nT" on the 3'end, are also conserved in Caelifera. In other ensiferans exist a common feature with a long T-stretch (>17 bp) next to rrnS on the H-strand, bounded by a purine at either end.