Roles Of Actin Cytoskeleton In The Nonhost Resistance Of Pepper To Puccinia Striiformis F. SP. Tritici And Expression Of Actin-related Genes

Non-host resistance （NHR）, which endows plant immunity against the majority ofmicrobial pathogens, is the most common and durable form of plant resistance todisease-causing organisms. The cytoskeleton plays a key role in nonhost disease resistance.Histochemical methods were used to investigate the resistance responses in the nonhostinteraction of pepper with Puccinia striiformis f. sp. tritici （Pst）. Before inoculation, pepperleaves were treated with actin polymerization inhibitor Latrunculin B （LB） to reveal the roleof cytoskeleton in nonhost resistance. Expression profiles of actin-related genes were assayedby quantitative RT-PCR （qRT-PCR）. Our study revealed the role of microfilaments innonhost pepper against wheat stripe rust pathogen remote relation, leading to acomprehensive understanding of nonhost resistance in pepper.1. Resistance responses in nonhost pepper and incompatible host wheat against the striperust fungus Pst were studied histochemically. Similarly high germination rates of the Pst wereobserved on both nonhost and resistant host. The significant difference between nonhost andincompatible host started to be observed from the stage of substomatal vesicle formation. Theformation of substomatal vesicles decreased evidently in the nohost pepper, followed by areduction of germ tubes generation and a scarce production of haustoria, which isaccompanied with a higher incidence of H₂O₂accumulation and hypersensitive response （HR）in pepper. In contrast to the nonhost pepper against Pst, a higher proportion of Pst formedsubstomatal vesicles and haustoria in incompatible wheat, but the ratio of H₂O₂accumulationor HR production were both lower than those in the nonhost pepper. This study revealed thatHR generation and H₂O₂accumulation are also the main resistance mechanisms for pepperagainst the non-adapted rust fungus Pst, which indicate that nonhost and host resistance sharethe similar resistance mechanisms.2. wheat leaves were treated with actin polymerization inhibitor LB before inoculation.The obvious differences between LB treatment and control were detected in the formation ofinfection sites and haustoria, accumulation of H₂O₂and occurrence of HR. Compared to thecontrol, though the rates of the formation of substomatal vesicles and haustoria were higher,the occurrence of hydrogen peroxide accumulation was delayed and the incidence of hypersensitive cell death was reduced in LB treatment. These results indicated thatmicrofilaments are closely related to the infection structure formation of non-adaptedpathogen, H₂O₂accumulation and HR production. Microfilaments play important roles inpepper resistance to the infection of non-adapted pathogen.3. ADF, Profilin and Rho as candidate genes related to microfilaments exhibitedsignificantly different expression levels during the nonhost interaction between pepper andPst by qRT-PCR. The down-regulated expression of ADF was detected at each time-pointexcept24hai. Profilin and Rho exhibited up-regulated expression at most time-points, butwith different expression levels and expression activationtime. Real-time PCR analysisrevealed that genes related to microfilaments participate in nonhost resistance of pepperagainst Pst, and genes may regulate microfilaments to stimulate intracellular hydrogenperoxide accumulation and HR production.