Comparison of the Microbiome and Metabolome in the Phloem of Straight and Twisted Trunks of Pinus yunnanensis Franch

Pinus yunnanensis Franch. is a common woodland species in the southwest of China. Its trunk frequently twists during growth, affecting timber quality. The explanation for the twisted-trunk formation is unknown. In this work, we examined the variety of endophytes and metabolites by comparing the straight and twisted trunk types of P. yunnanensis. The results showed that the twisted trunk had a distinct endosymbiont composition compared to the straight trunk. Pseudomonas and Craurococcus bacteria, as well as the fungus taxa Phaeosphaeria and Epichloë, spread significantly more in the twisted trunk compared to the straight trunk. However, there was less Dechloromonas in the twisted trunk. Metabolomic analysis revealed differences in metabolites in the straight and twisted trunks, which were associated with four metabolic pathways: beta-alanine metabolism, metabolism of Jasmonic acid and trans-Zeatin metabolism, linoleic acid metabolism, and pentose phosphate pathway. The compounds were linked to certain endophyte bacteria species. Our findings suggested that the twisted trunk was subjected to more stress than the straight trunk because of endosymbionts. Moreover, we speculated that hormone signal transduction and the absorption, transport, and utilization of phosphorus elements and their interaction with microorganisms may be closely connected to the formation of twists. This is the first study to characterize the microbiome and metabolome in the twisted trunks of P. yunnanensis, and the results enhance our understanding of the underlying causes of twisted-trunk formation in P. yunnanensis.