The complete mitochondrial genome of Melon thrips, Thrips palmi (Thripinae) and comparative analysis: A vector for Tospoviruses

Abstract

The melon thrips, Thrips palmi is a serious pest and vector for plant viruses on a wide range of economically important crops. DNA barcoding evidenced the presence of cryptic diversity in T. palmi and that warrants exhaustive molecular data. Our present study is on decoding the first complete mitochondrial genome of T. palmi (15,333 bp) through NGS technology. The mitogenome contains 37 genes, including 13 PCGs, two rRNAs, 22 tRNAs, and two control regions. The comparative analyses were conducted for gene arrangements, nucleotide composition, codon usage and phylogenetic relationship with other thrips mitogenomes. The nucleotide composition was 78.29% AT, and 21.72% GC with positive AT skewness (0.09) and negative GC skewness (-0.06). The ATN initiation codons were observed in 12 PCGs except cox1 with unique start codon (TTG). The RSCU analysis revealed Phe, Leu, Ile, Tyr, Asn, Lys and Met were the most frequently used amino acids in all PCGs. The codon CGG (Arg) was absent in T. palmi as compared to other thrips mitogenomes. The Ka/Ks ratio ranges from 0.078 in cox1 to 0.913 in atp8. We observed the typical cloverleaf secondary structure in most of the tRNA genes with a few exceptions; absence of DHU stem and loop in trnV and trnS, absence of DHU loop in trnE, lack of T-arm and loop in trnN. The position of trnS1 (between cox3 and CR2) is unique in T. palmi among all the studied thrips mitogenomes. The mitogenome contained 24 intergenic spacer regions and 12 overlapping regions. The CR2 is 63.77% similar to CR1, indicating a possible duplication and translocation in control region. Both the ML and BI phylogenetic trees revealed the close relationships of Thrips with Scirtothrips as compared to Frankliniella. Thus, more mitogenomes on the diverse thrips species is required to understand the in-depth phylogenetic and evolutionary relationships.