The complete nucleotide sequence of the chloroplast genome of potato Solanum tuberosum L. cv. Desiree was determined. The circular double-stranded DNA, which consists of 155,312 bp, contains a pair of inverted repeat regions (IRa, IRb) of 25,595 bp each. The inverted repeat regions are separated by small and large single copy regions of 18,373 and 85,749 bp, respectively. The genome contains 79 proteins, 30 tRNAs, 4 rRNAs, and unidentified genes. A comparison of chloroplast genomes of seven Solanaceae species revealed that the gene content and their relative positions of S. tuberosum are similar to the other six Solanaceae species. However, undefined open reading frames (ORFs) in LSC region were highly diverged in Solanaceae species except N. sylvestris. Detailed comparison was identified by numerous indels in the intergenic regions that were mostly located in the LSC region. Among them, a single large 241-bp deletion, was not associated with direct repeats and found in only S. tuberosum, clearly discriminates a cultivated potato from wild potato species Solanum bulbocastanum. The extent of sequence divergence may provide the basis for evaluating genetic diversity within the Solanaceae species, and will be useful to examine the evolutionary processes in potato landraces.
Thanatin is an antimicrobial peptide (AMP) generated by insects for defense against bacterial infections. In the present study, we performed cDNA cloning of thanatin and found the presence of multiple precursor proteins from the bean bug, Riptortus pedestris. The cDNA sequences encoded 38 precursor proteins, generating 13 thanatin isoforms. In the phylogenetic analysis, thanatin isoforms were categorized into two groups based on the presence of the membrane attack complex/perforin (MACPF) domain. In insect-bacterial symbiosis, specific substances are produced by the immune system of the host insect and are known to modulate the symbiont’s population. Therefore, to determine the biological function of thanatin isoforms in symbiosis, the expression levels of three AMP genes were compared between aposymbiotic insects and symbiotic R. pedestris. The expression levels of the thanatin genes were significantly increased in the M4 crypt, a symbiotic organ, of symbiotic insects upon systemic bacterial injection. Further, synthetic thanatin isoforms exhibited antibacterial activity against gut-colonized Burkholderia symbionts rather than in vitro-cultured Burkholderia cells. Interestingly, the suppression of thanatin genes significantly increased the population of Burkholderia gut symbionts in the M4 crypt under systemic Escherichia coli K12 injection. Overgrown Burkholderia gut symbionts were observed in the hemolymph of host insects and exhibited insecticidal activity. Taken together, these results suggest that thanatin of R. pedestris is a host-derived symbiotic factor and an AMP that controls the population of gut-colonized Burkholderia symbionts.
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