A novel metabolomics approach as integrative strategy for understanding changes in Pinus radiata D.Don metabolome in response to infestation by Sirex noctilio F.

Abstract

The production of renewable resources in forest plantations is one of Chile's most important industrial activities since it serves as the basis for essential primary industries such as wood, boards, pulp and chips. Consistent with the global trend, our country’s most extensive commercial plantations are monoculture forests, with Pinus radiata as the predominant planted species. Plantations of the species account for more than fifty per cent of the commercial plantations registered by 2021. Productivity and long-term viability of the forest economic sector in Chile, based on P. radiata plantations, are constantly threatened by droughts, fires, and disease outbreaks caused by exotic pests. Among these harmful pests, the insect Sirex noctilio (S. noctilio) may cause significant economic losses because it can kill trees quickly after just one infestation. The primary focus of scientific research regarding S. noctilio has been its symbiotic relationship with the fungus Amylostereum areolatum and the composition and physiological effects of the venom injected during oviposition. However, no studies have been published describing the biochemical processes triggered in the plant during infection. It is so far unknown the resistance and tolerance traits induced in Pinus radiata metabolome after S. noctilio infestation. Therefore, in the present thesis, we report the usefulness of LC-MS-based untargeted metabolomics for uncovering the systemic metabolome changes in needles (leaves) and wood of 14-year-old P. radiata trees in response to initial and long-term S. noctilio infestation. Needles suffered severe consequences from the chlorosis degrading photosystems after infestation. Photoprotection was immediately induced via up-regulation of catechin and procyanidin B1. Also, proline serves as an alternative substrate for respiration. In addition, extraordinary oxidative stress was also registered by an acute decrease in ascorbate levels (90-fold). Detoxification of venom toxin (noctilisin) via conjugation with glutathione (dropped by 17-fold) was hypothesized preceding the inevitable premature senescence observed within infested trees. Nonetheless, significant overexpression of auxins was detected, suggesting the activation of a tolerance mechanism. Finally, we evidenced that metabolomics accurately revealed the biochemical response of trees to the woodwasp infestation, indicating, in addition, the upstream molecular functions involved in the biochemical processes, as well as potentially new research and breeding targets.