New insights into the role of constitutive bacterial rhizobiome and phenolic compounds in twoPinusspp. with contrasting susceptibility to pine pitch canker

Abstract

The rhizobiome is being increasingly acknowledged as a key player in plant health and breeding strategies. The pine pitch canker (PPC), caused by the fungus Fusarium circinatum, affects pine species with varying susceptibility degrees. Our aims were to explore the bacterial rhizobiome of a susceptible (Pinus radiata) and a resistant (Pinus pinea) species together with other physiological traits, and to analyze shifts upon F. circinatum inoculation. Pinus seedlings were stem inoculated with F. circinatum spores and needle gas exchange and antioxidant-related parameters were analyzed in non-inoculated and inoculated plants. Rhizobiome structure was evaluated through 16S rRNA gene massive parallel sequencing. Species (non-inoculated plants) harbored distinct rhizobiomes (<40% similarity), where P. pinea displayed a rhizobiome with increased abundance of taxa described in suppressive soils, displaying plant-growth-promoting (PGP) traits and/or antifungal activity. Plants of this species also displayed higher levels of phenolic compounds. Fusarium circinatum induced slight changes in the rhizobiome of both species and a negative impact in photosynthetic-related parameters in P. radiata. We concluded that the rhizobiome of each pine species is distinct and higher abundance of bacterial taxa associated to disease protection was registered for the PPC-resistant species. Furthermore, differences in the rhizobiome are paralleled by a distinct content in phenolic compounds, which are also linked to plants’ resistance against PPC. This study unveils a species-specific rhizobiome and provides insights to exploit the rhizobiome for plant selection in nurseries and for rhizobiome-based plant-growth-promoting strategies, boosting environmentally friendly disease control strategies.

Comparative proteomics of Pinus–Fusarium circinatum interactions reveal metabolic clues to biotic stress resistance

“…In addition, the Chalcone-flavone isomerase family protein, involved in flavonoids biosynthesis, and the Probable pyridoxal 5 0 -phosphate synthase subunit PDX1 correlated with water and PSII status maintenance in inoculated P. pinea (Figure 5A). Anthocyanins and constitutive flavonoids antioxidant properties have been associated to P. pinea resistance PPC (Amaral et al 2019a(Amaral et al , 2019bLeitão et al 2021). PDX1 participates in vitamin B6 biosynthesis, a vital cofactor to several metabolic reactions and an effective antioxidant (Vanderschuren et al 2013) implicated in disease resistance (Zhang et al 2015) and in biotic stress resistance induction after exogenous application (Hong et al 2016;Pushpalatha et al 2007).…”

“…Therefore, using a well-characterised experimental system (Amaral et al 2019a(Amaral et al , 2019b(Amaral et al , 2020aCerqueira et al 2017;Leitão et al 2021), we aimed to compare the needle proteomes of the susceptible P. radiata and of the resistant P. pinea upon inoculation with F. circinatum by GeLC-Orbitrap/MS analysis following up-to-date multivariate and integrative analysis to highlight the main pathways that may explain the phenotypes observed. For this, quantitative physiological, hormonal and antioxidant enzymes activity data published elsewhere have also been considered (Amaral et al 2020a).…”

“…However, enzymatic antioxidants from the water-water and the Asc-GSH cycles do not seem to be involved in pine response to F. circinatum (Amaral et al 2020a). Rather, nonenzymatic antioxidants such as anthocyanins (Amaral et al 2019a(Amaral et al , 2019b and constitutive phenols (Leitão et al 2021) may assure redox protection in the PPC-resistant P. pinea.…”

Transcriptomics technologies and their potential for pine pitch canker management

“…In a recent study, although rhizobiomes of the F. circinatum-susceptible P. radiata and the resistant P. pinea species did not show significant changes after the stem inoculation of the pathogen, differences in the noninoculated plants were found. In particular, the resistant species hosted higher abundance of bacterial taxa associated to disease protection (Leitão et al, 2021). Therefore, further investigation about possible direct and indirect effects of microbiome on F. circinatum would be needed to assess the ecological importance of these biological populations for the disease development, and to evaluate possibilities to support pine resistance by microbiome manipulation.…”

“…In a recent study, although rhizobiomes of the F. circinatum-susceptible P. radiata and the resistant P. pinea species did not show significant changes after the stem inoculation of the pathogen, differences in the non-inoculated plants were found. In particular, the resistant species hosted higher abundance of bacterial taxa associated to disease protection (Leitão et al, 2021). Thus, microbial detection powered by the metagenomics technology could easily be employed to engineer microbiomes to reduce disease incidence or biopesticides to control specific pathogens (Klosterman et al, 2016).…”