Plant hormones play central roles in plant growth, developmental processes, and plant response to biotic and abiotic stresses. On the one hand, plant hormones may allocate limited resources to the most serious stresses; on the other hand, the crosstalks among multiple plant hormone signaling regulate the balance between plant growth and defense. Many studies have reported the mechanism of crosstalks between jasmonic acid (JA) and other plant hormones in plant growth and stress responses. Based on these studies, this paper mainly reviews the crosstalks between JA and other plant hormone signaling in regulating the balance between plant growth and defense response. The suppressor proteins JASMONATE ZIM DOMAIN PROTEIN (JAZ) and MYC2 as the key components in the crosstalks are also highlighted in the review. We conclude that JA interacts with other hormone signaling pathways [such as auxin, ethylene (ET), abscisic acid (ABA), salicylic acid (SA), brassinosteroids (BRs), and gibberellin (GA)] to regulate plant growth, abiotic stress tolerance, and defense resistance against hemibiotrophic pathogens such as Magnaporthe oryzae and Pseudomonas syringae. Notably, JA may act as a core signal in the phytohormone signaling network.

The physiological and metabolic processes of host plants are manipulated and remodeled by phytopathogenic fungi during infection, revealed obvious signs of biotrophy of the hemibiotrophic pathogen. As we known that effector proteins play key roles in interaction of hemibiotrophic fungi and their host plants. BAS4 (biotrophy-associated secreted protein 4) is an EIHM (extrainvasive hyphal membrane) matrix protein that was highly expressed in infectious hyphae. In order to study whether BAS4 is involved in the transition of rice blast fungus from biotrophic to necrotrophic phase, The susceptible rice cultivar Lijiangxintuanheigu (LTH) that were pre-treated with prokaryotic expression product of BAS4 and then followed with inoculation of the blast strain, more serious blast disease symptom, more biomass such as sporulation and fungal relative growth, and lower expression level of pathogenicity-related genes appeared in lesion of the rice leaves than those of the PBS-pretreated-leaves followed with inoculation of the same blast strain, which demonstrating that BAS4 invitro changed rice defense system to facilitate infection of rice blast strain. And the susceptible rice cultivar (LTH) were inoculated withBAS4-overexpressed blast strain, we also found more serious blast disease symptom and more biomass also appeared in lesion of leaves inoculated with BAS4-overexpressed strain than those of leaves inoculated with the wild-type strain, and expression level of pathogenicity-related genes appeared lower in biotrophic phase and higher in necrotrophic phase of infection, indicating BAS4 maybe in vivo regulate defense system of rice to facilitate transition of biotrophic to necrotrophic phase. Our data demonstrates that BAS4 in vitro and in vivo participates in transition from the biotrophic to the necrotrophic phase of Magnaporthe oryzae.

The effector proteins secreted by a pathogen not only promote virulence and infection of the pathogen, but also trigger plant defense response. Therefore, these proteins could be used as important genetic resources for transgenic improvement of plant disease resistance. Magnaporthe oryzae systemic defense trigger 1 (MoSDT1) is an effector protein. In this study, we compared the agronomic traits and blast disease resistance between wild type (WT) and MoSDT1 overexpressing lines in rice. Under control conditions, MoSDT1 transgenic lines increased the number of tillers without affecting kernel morphology. In addition, MoSDT1 transgenic lines conferred improved blast resistance, with significant effects on the activation of callose deposition, reactive oxygen species (ROS) accumulation and cell death. On the one hand, overexpression of MoSDT1 could delay biotrophy–necrotrophy switch through regulating the expression of biotrophy-associated secreted protein 4 (BAS4) and Magnaporthe oryzaecell death inducing protein 1 (MoCDIP1), and activate plant defense response by regulating the expression of Bsr-d1, MYBS1, WRKY45, peroxidase (POD), heat shock protein 90 (HSP90), allenoxide synthase 2 (AOS2), phenylalanine ammonia lyase (PAL), pathogenesis-related protein 1a (PR1a) in rice. On the other hand, overexpression of MoSDT1 could increase the accumulation of some defense-related primary metabolites such as two aromatic amino acids (L-tyrosine and L-tryptohan), 1-aminocyclopropane carboxylic acid, which could be converted to ethylene, vanillic acid and L-saccharopine. Taken together, overexpression of MoSDT1 confers improved rice blast resistance in rice, through modulation of callose deposition, ROS accumulation, the expression of defense-related genes, and the accumulation of some primary metabolites.

Background: Some of the pathogenic effector proteins play an active role in stimulating the plant defense system to strengthen plant resistance. Results: In this study, ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC/Q-TOF-MS) was implemented to identify altered metabolites in transgenic rice containing over-expressed M. oryzae Systemic Defense Trigger 1 (MoSDT1) that was infected at three-time points. The characterized dominating metabolites were organic acids and their derivatives, organic oxygen compounds, lipids, and lipid-like molecules. Among the identified metabolites, shikimate, galactinol, trehalose, D-mannose, linolenic acid, dopamine, tyramine, and L-glutamine are precursors for the synthesis of many secondary defense metabolites Carbohydrate, as well as amino acid metabolic, pathways were revealed to be involved in plant defense responses and resistance strengthening. Conclusion: The increasing salicylic acid (SA) and jasmonic acid (JA) content enhanced interactions between JA synthesis/signaling gene, SA synthesis/receptor gene, raffinose/fructose/sucrose synthase gene, and cell wall-related genes all contribute to defense response in rice. The symptoms of rice after M. oryzae infection were significantly alleviated when treated with six identified metabolites, i.e., galactol, tyramine, L-glutamine, L-tryptophan, α-terpinene, and dopamine for 72 h exogenously. Therefore, these metabolites could be utilized as an optimal metabolic marker for M. oryzae defense.