Local and systemic regulation of PSII efficiency in triticale infected by the hemibiotrophic pathogen Microdochium nivale

Microdochium nivale is a fungal pathogen that causes yield losses of cereals during winter. Cold hardening under light conditions induces genotype‐dependent resistance of a plant to infection. We aim to show how photosystem II (PSII) regulation contributes to plant resistance. Using mapping population of triticale doubled haploid lines, three M. nivale strains and different infection assays, we demonstrate that plants that maintain a higher maximum quantum efficiency of PSII show less leaf damage upon infection. The fungus can establish necrotrophic or biotrophic interactions with susceptible or resistant genotypes, respectively. It is suggested that local inhibition of photosynthesis during the infection of sensitive genotypes is not balanced by a supply of energy from the tissue surrounding the infected cells as efficiently as in resistant genotypes. Thus, defence is limited, which in turn results in extensive necrotic damage. Quantitative trait loci regions, involved in the control of both PSII functioning and resistance, were located on chromosomes 4 and 6, similar to a wide range of PSII‐ and resistance‐related genes. A meta‐analysis of microarray experiments showed that the expression of genes involved in the repair and de novo assembly of PSII was maintained at a stable level. However, to establish a favourable energy balance for defence, genes encoding PSII proteins resistant to oxidative degradation were downregulated to compensate for the upregulation of defence‐related pathways. Finally, we demonstrate that the structural and functional integrity of the plant is a factor required to meet the energy demand of infected cells, photosynthesis‐dependent systemic signalling and defence responses.     

Comparative proteomics combined with analyses of transgenic plants reveal ZmREM1.3 mediates maize resistance to southern corn rust

Southern corn rust (SCR), which is a destructive disease caused by Puccinia polysora Underw. (P. polysora), commonly occurs in warm‐temperate and tropical regions. To identify candidate proteins related to SCR resistance and characterize the molecular mechanisms underlying the maize–P. polysora interaction, a comparative proteomic analysis of susceptible and resistant maize lines was performed. Statistical analyses revealed 1489 differentially abundant proteins in the resistant line, as well as 1035 differentially abundant proteins in the susceptible line. After the P. polysora infection, the abundance of one remorin protein (ZmREM1.3) increased in the resistant genotype, but decreased in the susceptible genotype. Plant‐specific remorins are important for responses to microbial infections as well as plant signalling processes. In this study, transgenic maize plants overexpressing ZmREM1.3 exhibited enhanced resistance to the biotrophic P. polysora. In contrast, homozygous ZmREM1.3 UniformMu mutant plants were significantly more susceptible to P. polysora than wild‐type plants. Additionally, the ZmREM1.3‐overexpressing plants accumulated more salicylic acid (SA) and jasmonic acid (JA). Moreover, the expression levels of defence‐related genes were higher in ZmREM1.3‐overexpressing maize plants than in non‐transgenic control plants in response to the P. polysora infection. Overall, our results provide evidence that ZmREM1.3 positively regulates maize defences against P. polysora likely via SA/JA‐mediated defence signalling pathways. This study represents the first large‐scale proteomic analysis of the molecular mechanisms underlying the maize–P. polysora interaction. This is also the first report confirming the remorin protein family affects plant resistance to SCR.     

Sporisorium scitamineum colonisation of sugarcane genotypes susceptible and resistant to smut revealed by GFP‐tagged strains

Sporisorium scitamineum is the causal agent of sugarcane smut disease. The fungus establishes a biotrophic interaction with sugarcane tissues, and unlike smut fungi of other monocot hosts, the primary meristem of sugarcane plants develops a whip‐like structure instead of a tumour‐like galls emerging from floral structures (tassels and ears). We examined (GFP)‐tagged S. scitamineum infecting tissues of three sugarcane genotypes with distinct responses to smut (susceptible, intermediate resistant and resistant). Mating compatible haploid cells gfp‐expressing were obtained by Agrobacterium tumefaciens‐mediated transformation (ATMT) using the integrative vector pFAT‐gfp. Regardless of the inoculation method (drop inoculation and hypodermal syringe inoculation), all genotypes were colonised by the fungus. GFP‐tagged strains of opposite mating reaction were able to: (a) grow in vitro as fluorescent yeast‐like cells; (b) generate infectious dikaryon; (c) penetrate sugarcane tissues; (d) colonise tissues by growing a filamentous network; and (e) form the characteristic highly branched hyphae within host cells. Fungal colonisation 160 DAI revealed an association of the fungus with vascular vessels disrupting their organisation in all three genotypes analysed. However, the resistant plants did not develop whips spanning the experiment time. The first whips emerged 76 DAI from plants of the susceptible genotype whereas for intermediate resistant plants whips were detected at 137 DAI. These whips were dissected and fluorescent sporogenesis and teliospore maturation were analysed. In vitro germination of recovered teliospores revealed after meiosis the formation of a three‐celled hyphal filament, where the fourth cell was likely maintained in the teliospore coat. These cells showed independent segregation of the gfp marker, as a result of gfp insertions in different chromosomes of each compatible haploid strain. This work presents the complete fungal life cycle of GFP‐marked S. scitamineum to study developmental stages in planta.     

Feeding‐induced changes in defence enzymes and PR proteins and their implications in host resistance to Nilaparvata lugens

Six rice genotypes showing susceptible and resistant reactions to brown planthopper (BPH), Nilaparvata lugens were studied for feeding‐induced changes in defence enzymes and pathogenesis‐related (PR) proteins. The high resistant genotypes PTB 33, ADT 45 and ASD 7 and moderately resistant genotypes CO 43 and KAU 1661 recorded the greater expression of defence enzymes peroxidase, polyphenol oxidase, phenylalanine ammonia lyase, total phenol and β‐1,3 glucanase in response to N. lugens feeding at 1 day after infestation (DAI) compared with susceptible genotype TN1. The greater activity of chitinase was observed in resistant cultivars at 3 DAI and the activity was sustained for more than 1 week compared with susceptible TN1. In conclusion, the current study revealed that these defence enzymes and PR proteins might attribute to the resistance mechanisms in rice plants against BPH infestation.     

Transcriptomic and Proteomic Analyses of Resistant Host Responses in Arachis diogoi Challenged with Late Leaf Spot Pathogen,Phaeoisariopsis personata

Late leaf spot is a serious disease of peanut caused by the imperfect fungus, Phaeoisariopsis personata. Wild diploid species, Arachis diogoi. is reported to be highly resistant to this disease and asymptomatic. The objective of this study is to investigate the molecular responses of the wild peanut challenged with the late leaf spot pathogen using cDNA-AFLP and 2D proteomic study. A total of 233 reliable, differentially expressed genes were identified in Arachis diogoi. About one third of the TDFs exhibit no significant similarity with the known sequences in the data bases. Expressed sequence tag data showed that the characterized genes are involved in conferring resistance in the wild peanut to the pathogen challenge. Several genes for proteins involved in cell wall strengthening, hypersensitive cell death and resistance related proteins have been identified. Genes identified for other proteins appear to function in metabolism, signal transduction and defence. Nineteen TDFs based on the homology analysis of genes associated with defence, signal transduction and metabolism were further validated by quantitative real time PCR (qRT-PCR) analyses in resistant wild species in comparison with a susceptible peanut genotype in time course experiments. The proteins corresponding to six TDFs were differentially expressed at protein level also. Differentially expressed TDFs and proteins in wild peanut indicate its defence mechanism upon pathogen challenge and provide initial breakthrough of genes possibly involved in recognition events and early signalling responses to combat the pathogen through subsequent development of resistivity. This is the first attempt to elucidate the molecular basis of the response of the resistant genotype to the late leaf spot pathogen, and its defence mechanism.     

Identification of genes differentially expressed during interaction of resistant and susceptible apple cultivars (Malus × domestica) with Erwinia amylovora

Background  

The necrogenic enterobacterium, Erwinia amylovora is the causal agent of the fire blight (FB) disease in many Rosaceaespecies, including apple and pear. During the infection process, the bacteria induce an oxidative stress response with kinetics similar to those induced in an incompatible bacteria-plant interaction. No resistance mechanism to E. amylovora in host plants has yet been characterized, recent work has identified some molecular events which occur in resistant and/or susceptible host interaction with E. amylovora: In order to understand the mechanisms that characterize responses to FB, differentially expressed genes were identified by cDNA-AFLP analysis in resistant and susceptible apple genotypes after inoculation with E. amylovora.     

Biochemical Changes in Leaf Tissues of Taro [Colocasia esculenta L. (Schott)] Infected with Phytophthora colocasiae

The changes in some biochemical parameters due to Phytophthora leaf blight infection were assessed in leaf tissues of one resistant (DP‐25), two moderately resistant (Duradim and Jhankri) and one susceptible (N‐118) genotypes of taro [Colocasia esculenta (L.) Schott]. Phytophthora spore suspension (15 000 spore/ml water) was sprayed onto the in vitro raised taro plantlets at 30 days after establishment in pots to induce disease. In comparison with the uninoculated leaves, blight infected leaves showed reduction in protein content and activity of nitrate reductase and increase in total soluble sugar, reducing sugar content and activities of acid phosphatase and alkaline phosphatase among the studied genotypes. Changes in biochemical parameters under induced blight stress as compared with uninoculated control were less in resistant genotypes than that in susceptible genotype. The deviations in biochemical contents were highest in susceptible genotype N‐118. Based on the variations of above parameters under stress and non‐stress control among the four tested genotypes, the overall pattern of changes was N‐118 > Duradim > Jhankri > DP‐25, which is in accordance with the pattern of increasing resistance. The resistant genotypes could be used for commercial cultivation and genetic improvement programme to develop resistant varieties to Phytophthora leaf blight disease.