Understanding the role of methyl jasmonate and its inhibitors on pine defense against the pinewood nematode

Abstract

In the past years, the emergence of novel invasive species has become one of the most important threats to forest ecosystems. One of the major pests that has been introduced in the European conifer forest is the pinewood nematode Bursaphelenchus xylophilus (NMP). Recent studies have demonstrated that the jasmonic acid (JA) pathway seems to play a very important role in pine trees defence against B. xylophilus. In fact, it was suggested that exogenous application of methyl jasmonate (MeJa), a jasmonic acid (JA) analogue, to P. pinaster plants changes the plant phenotype from highly susceptible to B. xylophilus to moderately tolerant. Perhaps in this plant species the low tolerance to B. xylophilus may be due to an inefficient activation of the JA pathways. To test this hypothesis, two experimental trial were designed: 1) understand how exogenous application of MeJa and its inhibitors diethyldithiocarbamic acid (DIECA) and n-propyl gallate (nPG) impacted the production of defence-related metabolites (chlorophylls, carotenoids, polyphenols, flavonoids, anthocyanins, lignin, saponins, malondialdehyde) and gene expression (SAMS1, csAPX, ACO, PAL), in healthy P. pinaster and P. pinea plants; 2) evaluate the performance of PWN in Pinus spp. plants with reported distinct susceptibility to the disease, after treatment with MeJa, DIECA or nPG. In general, P. pinaster plants treated with 50 mM MeJa had higher total soluble polyphenols concentration in leaves (ca. 61%) and lignin content in leaves, stems and roots (by at least 50%), compared with control plants (treated with water). In P. pinea MeJa treated plants lignin concentration was also 70% higher than in control plants. Additionally, in this plant species saponins content was 67% higher in MeJa treated plants, compared with controls. Contrastingly, DIECA and nPG application decreased flavonoids concentration in P. pinaster leaves and P. pinea roots (by at least 20%), anthocyanins concentration in P. pinaster leaves (up to 38%) and lignin concentration in P. pinea leaves (by 35%). The relative expression of aminocyclopropanecarboxylate gene (ACO) was the most affected after plant treatment. MeJa treatment increased ACO expression in P. pinaster leaves (by 2.4-fold) and P. pinea leaves, stems and root (by 2,7-, 1- and 1,5-fold, respectively), whereas nPG increased ACO relative expression in P. pinea stems and root (by 2.8- and 0.4-fold respectively). Regarding the second part of this work, where the role of JA pathway in P. pinaster and P. pinea’s susceptibility to B. xylophilus was evaluated, P. pinaster showed higher susceptibility than P. pinea to the pathogen, attaining 164 ± 62 nematodes per gram of stem tissue at the end of experimental period, more 585% than P. pinea. Plant treatment with MeJa or its inhibitors did not induce significant alterations in nematode population during the experimental period. These results show that exogenous application of MeJa, DIECA and nPG could allow the manipulation of plant defence mechanisms, namely regarding the synthesis of polyphenols and lignin. Nevertheless, it was not possible to evaluate if the JA pathway is the key regulator of P. pinea defence mechanisms against B. xylophilus. The present work still provides novel information on how JA pathway influences the synthesis of defence-related metabolites and gene expression in plants.

Date of Award	30 Oct 2018
Original language	English
Awarding Institution	Universidade Católica Portuguesa
Supervisor	Marta Vasconcelos (Supervisor) & Luís Sampedro (Co-Supervisor)