Effect of elicitors on holm oak somatic embryo development and efficacy inducing tolerance to Phytophthora cinnamomi

Abstract

Holm oak trees (Quercus ilex L.) mortality is increasing worryingly in the Mediterranean area in the last years. To a large degree this mortality is caused by the oomycete Phytophthora spp., which is responsible for forest decline and dieback in evergreen oak forest areas of the southwestern Iberian Peninsula. This study is based on the possibility of applying chemical elicitors or filtered oomycete extracts to holm oak somatic embryos (SE) in order to induce epigenetic memory, priming, that may increase tolerance to the pathogen in future infections. To this end, we first examined the effect of priming treatments on SE development and its oxidative stress state, to avoid elicitors that may cause damage to embryogenic tissues. Both, the sterile oomycete extracts and the chemical elicitor methyl jasmonate (MeJA) did not produce any detrimental effect on SE growth and development, unlike the elicitors benzothiadiazole (BTH) and p-aminobenzoic acid (PABA) that reduced the relative weight gain and resulted in necrotic and deformed SE when were applied at high concentrations (25 µM BTH or 50 µM PABA) in accordance with their high malondialdehyde content. No significant differences among elicitation treatments were found in dual culture bioassays, although those SEs elicited with 50 µM MeJA increased H2O2 production after challenged against active oomycete indicating the activation of stress response. Since this elicitation treatment did not produce any adverse effect in the embryogenic process we suggest that could be used in further priming experiments to produce holm oak plants adapted to biotic stress.

Effect of Methyl Jasmonate in Gene Expression, and in Hormonal and Phenolic Profiles of Holm Oak Embryogenic Lines Before and After Infection With Phytophthora cinnamomi

“…Since plant defense responses have been reported to be mediated by H 2 O 2 production (Lin et al, 2005;Wang et al, 2015), and the role of reactive oxygen species (ROS) in plant resistance to fungal pathogens is wellestablished (Lehmann et al, 2015), the higher H 2 O 2 content in these MeJA treated embryos indicates activation of defense mechanisms. Corroborating this, we observed lower mycelium growth rates toward control than toward MeJA-elicited holm oak somatic embryos in dual cultures confronted to P. cinnamomi (Morcillo et al, 2020), although the oomycete development was not inhibited.…”

“…In this context, biotechnological tools such as somatic embryogenesis constitute an interesting alternative allowing clonal propagation of holm oak adult trees (Blasco et al, 2013;Barra-Jiménez et al, 2014;Martínez et al, 2017Martínez et al, , 2020Martínez et al, , 2021, although acclimatization of generated plants needs to be improved. Furthermore, combining somatic embryogenesis with chemical elicitors it is possible to induce resistance triggering natural plant defenses, as a complementary strategy to breeding programs developed to obtain resilient plant material (Morcillo et al, 2020). Induced resistance (IR) is a plant state associated with an enhanced ability to resist pests and pathogen attacks or abiotic stress after an inducing stimulus.…”

Induction of Radiata Pine Somatic Embryogenesis at High Temperatures Provokes a Long-Term Decrease in DNA Methylation/Hydroxymethylation and Differential Expression of Stress-Related Genes

“…Vernalization, in which cold exposure of winter annual plants synchronizes flowering to the optimal season, is a clear example [ 14 ]. Memory of pathogen attack, formerly referred to as systemic acquired resistance, is well documented [ 15 , 16 , 17 ], and the chemical priming of seeds to enhance stress tolerance and pathogen resistance of young plants after germination is a usual agronomic practice [ 3 ]. Some of the best-known examples of epigenetic memory in forest tree species are found in Norway spruce, for which the environmental conditions during both zygotic and somatic embryogenesis (SE) seem to modulate the timing of bud set and bud burst of plants years later [ 18 ].…”

Micropropagation, Characterization, and Conservation of Phytophthora cinnamomi-Tolerant Holm Oak Mature Trees

“…In vitro grown shoots, routinely maintained in glass jars with proliferation medium as previously described in Section 2.3, of two uncharacterized (E00 and E2) and two tolerant (PL-T2 and VA5) Q. ilex genotypes were employed in two experiments. Dual cultures were established with either three pairs of leaves or three shoots from one of the uncharacterized genotype controls and from a tolerant genotype, which were combined in Petri dishes (14 cm Ø and 2 cm high) containing Schenk and Hildebrand medium (SH) (Duchefa Biochemie) [42], and confronted with a section (0.5 cm side) of Pc mycelium in potato-dextrose-agar medium, as described by Morcilllo et al [35]. Each genotype was tested in 4 plates.…”

“…In vitro techniques, such as dual cultures, can also be applied to evaluate the pathogenicity of fungi and susceptibility of host plant genotypes as a complementary method [34]. Furthermore, this technique was used to study the potential of chemical elicitation treatments to induce defense responses to P. cinnamomi on holm oak embryogenic lines [35]. Plants have developed a multi-layered defense network to detect invading pathogens and stop them before they cause extensive damage.…”