Abstract
Induced resistance by elicitors is considered to be an eco-friendly strategy to stimulate plant defense against pathogen attack. In this study, we elucidated the effect of salicylic acid (SA) on induced resistance in rubber tree against Phytophthora palmivora and evaluated the possible defense mechanisms that were involved. For SA pretreatment, rubber tree exhibited a significant reduction in disease severity by 41%. Consistent with the occurrence of induced resistance, the pronounced increase in H2O2 level, catalase (CAT) and peroxidase (POD) activities were observed. For defense reactions, exogenous SA promoted the increases of H2O2, CAT, POD and phenylalanine ammonia lyase (PAL) activities, including lignin, endogenous SA and scopoletin (Scp) contents. However, SA had different effects on the activity of each CAT isoform in the particular rubber tree organs. Besides, three partial cDNAs encoding CAT (HbCAT1, HbCAT2 and HbCAT3) and a partial cDNA encoding PAL (HbPAL) were isolated from rubber tree. Moreover, the expressions of HbCAT1, HbPAL and HbPR1 were induced by SA. Our findings suggested that, upon SA priming, the elevated H2O2, CAT, POD and PAL activities, lignin, endogenous SA and Scp contents, including the up-regulated HbCAT1, HbPAL and HbPR1 expressions could potentiate the resistance in rubber tree against P. palmivora.
Highlights
In this Isntuthdiys, swtuediyn, vweestiingvaetsetdigathteedetfhfeecetffoefctSAof pSArimpriinmginognoindinudcuecdedrerseisitsatnancceeininrruubbbber treee against P. palmiavgoarainisnt fPe.cptiaolmni.vIonraoiunfrecptrioenli.mIninoaurrypsrteulidmyi,ntahrye setfufedcyt, othfeSeAffeocnt othf eSAleaonf othf erulebabf eorf trruebebseer etdreleings was tested wseitehdlvinagrsiowuasscteosntecdenwtritahtivoanriso(u0s,c5o,n1c0enatnradtio2n0sm(0M, 5),.1A0 fatnedr 120dmayMo).fAthfteertr1edaatmy oefntth,ethtreealetmavenest, of some salicylic acid (SA)-treattheedlepalvaenstsofasto1m0emSAM-traenadted20plmanMts asth1o0wmeMd laenadf 2s0hrminMkashgoew, wedhlielaeftshherrinekwagaes, wnohislehtrhinerkeinwgaseffect on no shrinking effect on leaves of SA treated with 5 mM (Figure 1A)
The full-length cDNA of PAL was isolated from Juglans regia containing 1935 bp and encoded 645-amino-acid protein [58]. These results indicated that the obtained HbCAT1 and H. brasiliensis phenylalanine ammonia lyase (HbPAL) were similar to catalase and phenylalanine ammonia lyase, respectively, with other plants
From our results and those aforementioned reports, we suggest that the SA-induced HbCAT1, HbPAL and HbPR1 gene expressions lead to the biosyntheses of defense-related enzymes and secondary metabolites, thereby inducing resistance in rubber tree against P. palmivora infection
Summary
Arg.) is one of the economically important crops in Thailand. Its products are currently exported worldwide and produce major revenue for the country. Phytophthora palmivora, an aggressive hemibiotrophic oomycete pathogen, is a causal agent of abnormal leaf fall and black stripe diseases of the rubber tree. It infects petioles causing extensive defoliation of the mature leaves within a few weeks and attacks tapping surfaces leading to dark vertical lines in the panels, thereby reducing plant growth and latex productivity, subsequently leading to significant economic loss [1]. Upon sensing of the invading pathogens, plants have evolved multitudinous constitutive and induced basal defense mechanisms to protect themselves against pathogen attack, for examples, oxidative bursts, defense signaling pathways, transcriptional expressions of pathogenesis-related (PR) genes, the accumulations of antimicrobial proteins; phytoalexins, and the depositions of lignin, suberin and callose to reinforce cell wall at the pathogen penetration site [2]
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