Sa Ja

On the basis of a JA-inducible EST, the full length cDNA of a putative protein kinase gene, OsSJMK1, was isolated from rice (Oryza sativa L.). The predicted protein of this gene, consisting of 498 amino acids with a predicted PI value of 8.43, contains a mitogen-activated protein kinase (MAPK) domain with a dual-phosphorylation activation motif TDY (Thr-Asp-Tyr) and a C-terminus domain that feature a typical MAPK belonging to subgroup V, OsSJMK1 showed 81% sequence identity to the reported BWMK1, a blast fungus and wounding inducible protein, in the N-terminus kinase domain but had low sequence identity in the C-terminus domain. Despite the high similarity of gene structure between OsSJMK1 and BWMK1, the expression of OsSJMK1 was weakly induced by blast fungus but not wounding, rather it was transiently induced by jasmonic acid (JA) and salicylic acid (SA) at early stages of treatment. This gene was not induced by other hormones (such as ABA) or abiotic stresses, such as drought and salinity. The low level of transcript of this gene was detected in the various tissues of rice. The results suggest that OsSJMK1 might be activated specifically by JA and SA and involved in defense signaling pathways.

The plant hormones salicylic acid (SA), also known as plant aspirin, and jasmonic acid (JA) play major roles in the regulation of the plant immune system. In general, SA is important for defense against pathogens with a biotrophic lifestyle, whereas JA is essential for defense against insect herbivores and pathogens with a necrotrophic lifestyle. Antagonistic and synergistic interactions between the

Arbuscular mycorrhizal fungi (AMF) and Trichoderma harzianum are known to affect plant growth and disease resistance through interaction with phytohormone synthesis or transport in the plant. Cross-talk between these microorganisms and their host plants normally occurs in nature and may affect plant resistance. Simultaneous quantification in the shoots of melon plants revealed significant changes in the levels of several hormones in response to inoculation with T. harzianum and two different AMF (Glomus intraradices and Glomus mosseae). Analysis of zeatin (Ze), indole-3-acetic acid (IAA), 1-aminocyclopropane-1-carboxylic acid (ACC), salicylic acid (SA), jasmonic acid (JA) and abscisic acid (ABA) in the shoot showed common and divergent responses of melon plants to G. intraradices and G. mosseae. T. harzianum effected systemic increases in Ze, IAA, ACC, SA, JA and ABA. The interaction of T. harzianum and the AMF with the plant produced a characteristic hormonal profile, which differed from that produced by inoculation with each microorganism singly, suggesting an attenuation of the plant response, related to the hormones SA, JA and ethylene. These results are discussed in relation to their involvement in biomass allocation and basal resistance against Fusarium wilt.Dual inoculation with arbuscular mycorrhizal fungi and Trichoderma harzianum results in a plant hormonal profile different from that associated with the inoculation with either agent applied singly.► Mycorrhizal establishment and Trichoderma harzianum–plant interaction imply changes in the shoot hormonal profile of melon plants. ► Colonisation of different AMF produces common and divergent plant responses. ► T. harzianum effected systemic increases in Ze, IAA, ACC, SA, JA and ABA shoot content. ► Co-inoculation with T. harzianum and AMF produces a characteristic shoot hormonal profile, which differs from that produced by single inoculation.

Plant resistance to pathogen infection can be achieved by systemic regulation of the defense-related genes that respond to specific systemic signals. To elucidate defense responses in chickpea (Cicer arietinum L.) against fungal pathogens, Ascochyta rabiei (Pass.) Labr. causing ascochyta blight and Fusarium oxysporum f.sp. ciceri causing fusarium wilt, expression patterns of defense-related genes in chickpea after pathogen inoculation and exogenous treatments with systemic signals such as SA and Me-JA were investigated. Two blight differentia germplasm lines, FLIP84-92C(2) (blight resistant and SA- and Me-JA-sensitive) and PI359075(1) (blight susceptible and SA- and Me-JA-insensitive) showed significant differential expression patterns of the defense-related genes after A. rabiei inoculation and exogenous treatment with SA and Me-JA. However, blight resistance in the recombinant inbred lines generated from the cross of the two germplasm lines did not cosegregate with the expression of the genes induced either by pathogen inoculation or by signal chemicals. Fusarium wilt resistance in chickpea also did not require induction of the defense-related genes after Fusarium infection. These results indicated that systemic regulation of the defense-related genes at transcription level which is reportedly associated with disease resistance in other model plant species such as Arabidopsis might not confer resistance in chickpea against two necrotrophic fungal pathogens, A. rabiei (Pass.) Labr and F. oxysporum f.sp. ciceri. Further studies focused on constitutive or unknown defense systems independent of SA- and JA-mediated systemic resistance mechanisms are required to understand fungal resistance mechanisms in chickpea.