A. Ramesh Sundar

Induction of pathogenesis-related proteins in sugarcane leaves and cell-cultures by a glycoprotein elicitor isolated from Colletotrichum falcatum

The induction of pathogenesis-related (PR) proteins in sugarcane (Saccharum officinarum L.) leaves and suspension-cultured cells in response to treatment with a glycoprotein elicitor isolated from Colletotrichum falcatum (the red rot pathogen) was investigated. Treatment of leaves and cells with the elicitor resulted in a much marked increase in the activities of chitinase and β-1,3-glucanase in red rot resistant (BO 91) than susceptible (CoC 671) sugarcane cultivar. SDS-PAGE analysis revealed that C. falcatum elicitor induced the accumulation of several proteins in suspension-cultured cells of resistant cultivar (BO 91); among them the 35 kDa protein was predominant. Whereas, a 27 kDa protein was induced predominantly in the cells of susceptible cultivar upon treatment with the elicitor. When sugarcane leaves were treated with C. falcatum elicitor, two proteins with apparent molecular masses of 25 and 27 kDa were induced both in the resistant and susceptible cultivars. However, the induction was stronger in the resistant than the susceptible cultivar. Immunoblot analysis for chitinase indicated that a protein with an apparent molecular mass of 37 kDa cross-reacting with barley chitinase antiserum was strongly induced in the suspension cultured cells of both the cultivars. The induction of 37 kDa chitinase was more in the cells of resistant cultivar than in the susceptible cultivar. Western blot analysis revealed that a 25 kDa thaumatin-like protein (TLP) cross-reacting with bean TLP antiserum was strongly induced in leaves and cultured cells of both resistant and susceptible cultivars due to elicitor treatment.

A Mini-Review on Smut Disease of Sugarcane Caused by Sporisorium scitamineum

Smut of sugarcane is caused by the fungus Ustilago scitmainea (Sydow, 1924). The first report of the disease incidence came from Natal, South Africa in 1877 as reported by Luthra et al., (1940) and it was speculated to be confined in the eastern hemisphere, until it was reported in Argentina. The disease spread is worldwide covering most of the sugarcane producing areas viz. Mauritius, Rhodesia, Indonesia, the islands of Java, Sulawesi and Sumbawa, etc. Until the 1950s, smut was of concern only in Asia, with an outlying population in Argentina. Since then, it has spread through South, Central, East and West Africa, where many of the areas not having focused breeding programme for smut resistance. In the 1970s and 1980s, it expanded to Hawaii, the Caribbean, the mainland USA, Central America and Southern Brazil. These outbreaks prompted a great deal of experimental work on sugarcane smut (Heinz, 1987). Subsequently, the occurrence of sugarcane smut in Morocco (Akalach, 1994) and Iran (Banihashemi, 1995) was established. The occurrence, prevalence and importance of the sugarcane smut pathogen have been highlighted by Antoine as early as 1961. The incidence of the disease was widespread covering several countries in East Africa, the Pacific and the Caribbean islands, wherein a severe outbreak of the disease resulted in devastating loss to the sugarcane plantations. Lovick (1978) comprehensively reviewed on various aspects of sugarcane smut viz. symptoms, yield reduction, causal organism, physiological races of the smut fungus, epidemiology, host resistance and management. It was reported that severe smut outbreak in the Caribbean has created an impact amongst cane growers and sugar industry.

Induction of systemic resistance toColletotrichum falcatum in sugarcane by a synthetic signal molecule, acibenzolar-S-Methyl(CGA-245704)

The effect of a novel synthetic signal molecule, acibenzolar-S-methyl (CGA-245704; benzo [1,2,3] thiadiazole-7-carbothioic acid S-methyl ester), in inducing resistance in sugarcane against red rot disease caused by the fungusColletotrichum falcatum Went was studied. Application of CGA-245704 as a soil drench or along with marcotting rooting mixture induced resistance in sugarcane to challenge inoculation withC. falcatum. When the pathogen was inoculated by the plug method, it caused discoloration in the untreated control stalk tissues; however, in the stalk tissues pretreated with acibenzolar-S-methyl, pathogen colonization was considerably reduced. When the pathogen was inoculated by nodal swabbing, its penetration was arrested in the sensitized stalk tissues. An induced systemic resistance effect was found to persist up to 30 days in the pretreated cut canes. Increased phenolic content and accumulation of pathogenesis-related (PR) proteins,viz., chitinase, β-1,3-glucanase and thaumatin-like protein (PR-5), were observed in sugarcane plants treated with acibenzolar-S-methyl.

Proteomic analysis of a compatible interaction between sugarcane and Sporisorium scitamineum

Smut caused by Sporisorium scitamineum is one of the important diseases of sugarcane with global significance. Despite the intriguing nature of sugarcane, S. scitamineum interaction, several pertinent aspects remain unexplored. This study investigates the proteome level alterations occurring in the meristem of a S. scitamineum infected susceptible sugarcane cultivar at whip emergence stage. Differentially abundant proteins were identified by 2DE coupled with MALDI‐TOF/TOF‐MS. Comprehensively, 53 sugarcane proteins identified were related to defence, stress, metabolism, protein folding, energy, and cell division; in addition, a putative effector of S. scitamineum, chorismate mutase, was identified. Transcript expression vis‐à‐vis the activity of phenylalanine ammonia lyase was relatively higher in the infected meristem. Abundance of seven candidate proteins in 2D gel profiles was in correlation with its corresponding transcript expression levels as validated by qRT‐PCR. Furthermore, this study has opened up new perspectives on the interaction between sugarcane and S. scitamineum.

Mechanism of resistance induced by plant activators against Colletotrichum falcatum in sugarcane

Abstract A search for plant activators capable of inducing systemic resistance in sugarcane showed that plants pre-treated with synthetic signal inducers confer a high degree of resistance to Colletotrichum falcatum – the red rot pathogen. Among the various treatments, Acibenzolar S- methyl (ASM) was found to be very effective in restricting the pathogen colonization inside the inoculated cane stalk tissues. The induction of resistance was accompanied by a significant increase in peroxidases and polyphenoloxidases activities. A considerable decrease of pathogen titre in the pre-treated tissues as determined by ELISA, clearly demonstrated the restriction of pathogen colonization and proliferation in the sensitized cane stalks. Specific induction of new isoforms of peroxidases and polyphenoloxidases in C. falcatum elicitor treatment indicates the pathogen elicitor induced specific cellular response of sugarcane suspension-cultured cells.

Induction of systemic acquired resistance (SAR) using synthetic signal molecules against Colletotrichum falcatum in sugarcane

Red rot of sugarcane caused by the fungal pathogen Colletotrichum falcatum is one of the major constraints in India and other South Asian countries. Studies were conducted under field conditions to induce systemic resistance against red rot of sugarcane using Benzo (1, 2, 3) thiadiazole — 7 — carbonic acid S — methyl ester (BTH) and salicylic acid (SA). The pre-treatment with these inducers significantly arrested the pathogen growth and reduced the disease severity in the pathogen-inoculated canes. Antifungal assay of tissue-bits from inducer treated canes showed clear inhibition of pathogen in the plates. The study on the possible mechanism(s) of induced resistance revealed induction of defense-related enzymes like phenylalanine ammonia-lyase (PAL), peroxidase (POX), polyphenol oxidase (PPO) and accumulation of phenolics in systemically protected sugarcane stalks. The study clearly established that, systemic acquired resistance holds a promise in managing red rot in elite commercial varieties under field conditions and it can be used as an effective management strategy for control of the disease in an environment expected to favour a disease outbreak.

Differential Regulation of Defense-Related Gene Expression in Response to Red Rot Pathogen Colletotrichum falcatum Infection in Sugarcane

Red rot is a serious disease of sugarcane caused by the fungus Colletotrichum falcatum imposing a considerable economic loss annually in all sugarcane-producing countries. In this study, we analyzed the early resistance response of sugarcane to red rot fungus by comparing the differences between control and inoculated stalk tissues. Differential display reverse transcription polymerase chain reaction (DD-RT-PCR) was employed to identify altered expression of genes in disease-resistant cv Co 93009, in response to pathogen infection. DD-RT-PCR identified 300 differentially expressed transcripts of which 112 were selected for further analysis. Cloning and sequence analysis of the isolated cDNA fragments resulted in functional categorization of these clones into five categories, of which the defense/stress/signaling group was the largest, with clones homologous to genes known to be actively involved in various pathogenesis-related functions in plant species. This group showed overexpression of several transcripts related to ethylene-mediated and jasmonic acid pathway of plant defense mechanisms. Of the 112 expressed sequence tags, validation of expression was carried out for five important genes whose role in plant defense mechanisms is well established. This is the first report of Colletotrichum-mediated gene regulation in sugarcane which has provided a set of candidate genes for detailed molecular dissection of signaling and defense responses in tropical sugarcane during the onset of red rot resistance.

Interaction between sugarcane and Colletotrichum falcatum causing red rot: Understanding disease resistance at transcription level

Detailed studies were taken up on host pathogen interaction between sugarcane and Colletotrichum falcatum causing red rot at the transcription level with a set of sugarcane varieties varying in disease resistance. A set of gene specific primers were designed to detect transcripts of resistance gene analogues (RGA’s), defense-related genes, transcription factors and signaling pathway genes induced during the host-pathogen interaction. mRNA extracted from pathogen inoculated canes at different time intervals were screened with 50 primers. Many of the transcripts were found to be expressed from the time of inoculation till 48h However, differential gene expression was found only for chitinase, metallothionein, R30 (RGA), receptor protein kinase, reversibly glycosylated protein and signal sequence hydrophobic region (SSHR) between resistant and susceptible varieties. Additionally differences in transcript size were noticed for some of the screened primers. We have standardized differential display (DD)-RT-PCR protocol with silver staining method to identify differential transcripts. Work on transcriptional variation in C. falcatum-sugarcane interaction has been performed for the first time and this promises a new approach to identify gene(s) involved in red rot resistance in sugarcane.

Isolation and identification of endophytic bacterial strains from sugarcane stalks and theirin vitro antagonism against the red rot pathogen

Forty nine isolates of endophytic bacteria and three isolates of rhizobacteria were isolated from different sugarcane varieties, clones ofSaccharum spontaneum andErianthus sp. All the bacterial isolates were evaluated for antagonism against the red rot pathogen of sugarcaneColletotrichum falcatum. The results showed that seven isolates were effective in inhibiting fungal mycelial growth underin vitro conditions. A major proportion of endophytic and rhizosphere isolates belonged to gram-positive rods. Biochemical characterization of the seven efficient antagonistic isolates revealed that three isolates viz., 687-2bl, 71-1-1a and 46-la2 belonged toPseudomonas aeruginosa, three isolates viz. SS1, SS2 and SS3 belonged toPseudomonas fluorescens and one isolate viz. 312-2b, wasPseudomonas putida.

Advances in proteomic technologies and their scope of application in understanding plant–pathogen interactions

Proteomics, one of the major tools of ‘omics’ is evolving phenomenally since the development and application of two-dimensional gel electrophoresis coupled with mass spectrometry at the end of twentieth century. However, the adoption and application of advanced proteomic technologies in understanding plant–pathogen interactions are far less, when compared to their application in other related fields of systems biology. Hence, this review is diligently focused on the advances in various proteomic approaches and their gamut of applications in different facets of phyto-pathoproteomics. Especially, the scope and application of proteomics in understanding fundamental concepts of plant–pathogen interactions such as identification of pathogenicity determinants (effector proteins), disease resistance proteins (resistance and pathogenesis-related proteins) and their regulation by post-translational modifications have been portrayed. This review, for the first time, presents a critical appraisal of various proteomic applications by assessing all phyto-pathoproteomics-related research publications that were published in peer-reviewed journals, during the period 2000–2016. This assessment has revealed the present status and contribution of proteomic applications in different categories of phyto-pathoproteomics, namely, cellular components, host–pathogen interactions, model and non-model plants, and utilization of different proteomic approaches. Comprehensively, the analysis highlights the burgeoning application of global proteome approaches in various crop diseases, and demand for acceleration in deploying advanced proteomic technologies to thoroughly comprehend the intricacies of complex and rapidly evolving plant–pathogen interactions.