Abstract
Pochonia chlamydosporia is a fungal parasite of nematode eggs. Studies have shown that some strains of Pochonia chlamydosporia can promote plant growth and induce plants’ systemic resistance to root-knot nematodes by colonizing in their roots. This study aimed to verify the effect of the PC-170 strain on tomato growth and systemic resistance. Split-root experiments were conducted to observe the systemic resistance induced by PC-170. To explore the defense pathway that was excited due to the colonization by PC-170, we tested the expression of marker genes for defense pathways, and used mutant lines to verify the role of plant defense pathways. Our results showed that PC-170 can colonize roots, and promotes growth. We found a role for jasmonic acid (JA) in modulating tomato colonization by PC-170. PC-170 can activate tomato defense responses to reduce susceptibility to infection by the root-knot nematode Meloidogyne incognita, and induced resistance to some pathogens in tomatoes. The marker genes of the defense pathway were significantly induced after PC-170 colonization. However, salicylic acid (SA)- and jasmonic acid (JA)-dependent defenses in roots were variable with the invasion of different pathogens. Defense pathways play different roles at different points in time. SA- and JA-dependent defense pathways were shown to cross-communicate. Different phytohormones have been involved in tomato plants’ responses against different pathogens. Our study confirmed that adaptive JA signaling is necessary to regulate PC-170 colonization and induce systemic resistance in tomatoes.
Highlights
Plants are constantly subjected to various attacks from phytopathogenic fungi, bacteria, and plant-parasitic nematodes
The induction of the Proteinase inhibitor II (PI II) gene in plants pre-inoculated with P. chlamydosporia strain 170 (PC-170) was stronger and more durable (Figure 8D). These results suggest that PC-170 primes jasmonic acid (JA)-dependent defense signaling in systemic root tissue, which probably affects the inhibitory effect on JA-mediated signaling by M. incognita
The results showed that the JA-deficient def1 mutant could a regain resistance to nematode infection in PC-170-pre-inoculated plants as a result of spraying with the exogenous hormone methyl jasmonate (MeJA)
Summary
Plants are constantly subjected to various attacks from phytopathogenic fungi, bacteria, and plant-parasitic nematodes. Plants are not entirely passive, because the plants themselves have a series of corresponding immune responses, and they benefit from endophytic fungi to modulate their interactions with pathogens. The ‘Invasion model’ in 2015 described the symbiotic relationship between pathogens and plants [2], while the ‘Spatial Immunity Model’ in 2019 defined immune signaling in plant–microbe interactions [3]. In addition to the induction of immunity in plants by the recognition of pathogenic effectors in host cells, plant roots benefit from endophytic and mycorrhizal fungi, which can provide plant hosts with nutrition and Microorganisms 2021, 9, 1882. Fungal endophytes improve seed germination, and promote root formation and plant growth by producing plant hormones such as indole-3-acetic acid (IAA) [5,6]
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