Symbiotic microbes aid host adaptation by metabolizing a deterrent host pine carbohydrate d -pinitol in a beetle-fungus invasive complex

Abstract

The red turpentine beetle (RTB) is one of the most destructive invasive pests in China and solely consumes pine phloem containing high amounts of d -pinitol. Previous studies reported that d -pinitol exhibits deterrent effects on insects. However, it remains unknown how insects overcome d -pinitol during their host plant adaptation. We found that d -pinitol had an antagonistic effect on RTB, which mainly relied on gallery microbes to degrade d -pinitol to enhance host adaptation with mutualistic Leptographium procerum and two symbiotic bacteria, Erwinia and Serratia , responsible for this degradation. Genomic, transcriptomic, and functional investigations revealed that all three microbes can metabolize d -pinitol via different branches of the inositol pathway. Our results collectively highlight the contributions of symbiotic microbes in RTB’s adaptation to living on pine, thereby facilitating outbreaks of RTB in China. These findings further enrich our knowledge of symbiotic invasions and contribute to the further understanding of plant-insect interactions.

G-Protein Coupled Receptor Gpr-1 Is Important for the Growth and Nutritional Metabolism of an Invasive Bark Beetle Symbiont Fungi Leptographium procerum

“…Our previous studies found that AMYG and SUC1 were involved in the hydrolyzation of starch to D-glucose, and iolT1, MIOX, PDA6, PDA9-1, and PDA9-2 participated in the D-pinitol utilization. 7,13 Consistent with our carbohydrate metabolic results, there were no differences in the genes involved in the starch to D-glucose conversion and D-pinitol metabolism between WT and ΔGpr-1 mutant, which suggested that Gpr-1 was not involved in the carbohydrate metabolism in L. procerum (Figure S5). As noted in the preceding results, loss of Gpr-1 caused a thicker cell wall of L. procerum.…”

“…The growing evidence has shown that associated microbes are required for growth, reproduction, host and environment adaptation, pesticide resistance, and triple interactions with plant and natural enemies of various destructive pests. 6,7,38 For example, primary endosymbiont Buchnera is required for the survival of its host aphid as it provides essential amino acids to its host. 38 Our serial studies on the RTB-L. procerum invasive complex have shown that L. procerum contributes to the outbreak of RTB in China from multiple aspects including pathogenicity, 3-carene induction, nutritional compensation, and deterrent degradation.…”

“…7,13 Our newly sequenced L. procerum genome was used as the reference genome. 7 The DESeq R package (1.18.0) was used for differential analyses of gene expression. DESeq provides statistical routines for determining the differential expression in digital gene expression data using a model based on the negative binomial distribution.…”

“…RTB mutualistic fungal strain L. procerum (CMW25614) was grown and maintained at 25 °C on malt extract agar (MEA) as previously described. ,,, …”

“…Sequences from Aspergillus fumigatus, Aspergillus flavus, and Beauveria bassiana were used for the phylogenetic tree construction. − Gene deletion of Gpr-1 in L. procerum was performed by homologous recombination as our previous studies described. , First, the homologous arms upstream and downstream of Gpr-1 were amplified using Q5 high-fidelity DNA polymerase (New England BioLab Inc.). The restriction enzyme sites of Sma I and Xba I were inserted into the homologous arms.…”