Temporal physiological response of pine toFusarium circinatuminfection is dependent on host susceptibility level: the role of ABA catabolism

Abstract

Pine pitch canker (PPC), caused by Fusarium circinatum Nirenberg & O’Donnell, represents an important threat to conifer forests worldwide, being associated with significant economic losses. Although essential to develop disease mitigation strategies, little research focused on host susceptibility/resistance mechanisms has been conducted. We aimed to explore the response of a highly susceptible (Pinus radiata) and a relatively resistant (Pinus pinea) species to F. circinatum infection at different stages of infection. Morpho-physiological, hormonal and oxidative stress-related changes were assessed for each pine species and sampling point. Most of the changes found occurred in symptomatic P. radiata, for which an increased susceptibility to photoinhibition was detected together with decreased superoxide dismutase (SOD) activity. Abscisic acid (ABA) catabolism was activated by F. circinatum inoculation in both pine species, leading to the accumulation of the inactive dihydrophaseic acid (DPA) in P. radiata and of the less-active phaseic acid (PA) in P. pinea. Hormones’ confocal analysis revealed that this strategy may be of particular importance at 6 dpi in P. pinea, which together with photosynthesis maintenance to fuel defence mechanism, could in part explain the species resistance to PPC. These results are of great interest for the development of hormone-based breeding strategies or to the use of hormone application as inducers of resistance to F. circinatum infection.

Dual RNA-Sequencing Analysis of Resistant (Pinus pinea) and Susceptible (Pinus radiata) Hosts during Fusarium circinatum Challenge

“…This highlights the importance of an integrated study of transcriptomic and physiological analysis that considers the post-transcriptional regulation. The general stomata opening and increased transpiration rate verified in P. pinea upon inoculation with F. circinatum in Amaral et al [ 46 ] are at odds with our results. The absence of these changes in our study may be explained by the different plant growing conditions or plant provenances.…”

“…ROS participates in defense response signaling, however, its excess may damage biomolecules and disrupt plant metabolism. Although some antioxidant systems were excluded from being part of Pinus defense against F. circinatum (e.g., ascorbate-glutathione cycle) [ 46 ], ascorbate seems to have an important role in our experimental system as genes related to L-ascorbate biosynthesis were only up-regulated in P. pinea . Concurrent with this, the production of antioxidant secondary metabolites (terpenoids) was represented with a high number of up-regulated terpene synthases in P. pinea .…”

“…Genes participating in JA biosynthesis such as OPR were up-regulated during pathogenesis, although to less extent in P. radiata . However, JA was not accumulated in the needles of any of these species at the early stages of PPC disease [ 46 ]. Nonetheless, the activation of root OPR genes was delayed in an apple tree genotype susceptible to Pythium ultimum infection [ 53 ], which could also be the case for the susceptible P. radiata in response to F. circinatum .…”

“…Amaral et al [ 46 ] showed that while the susceptible P. radiata suffered photosynthesis impairment once PPC symptoms occur, P. pinea was able to maintain its photosynthetic activity over time after F. circinatum inoculation. At the transcriptional level, the down-regulation of genes encoding RuBisCo, photosystem I reaction center subunit or chlorophyll a/b binding protein ( Table S19 ), due possibly to the higher levels of ethylene [ 69 ], could suggest a reduction in photosynthesis activity in P. pinea .…”

“…While symptomatic P. radiata and P. pinaster suffered a water deprivation-like scenario and photosynthetic limitation after F. circinatum infection, P. pinea opened their stomata, incrementing the transpiration and accumulated glycerol [ 19 ]. Furthermore, Amaral et al [ 46 ] suggested that ABA catabolism could play a key role in PPC overcome.…”