Old Enzyme, New Role: The β-Glucosidase BglC of Streptomyces scabiei Interferes with the Plant Defense Mechanism by Hydrolyzing Scopolin

The beta-glucosidase BglC fulfills multiple functions in both primary metabolism and induction of pathogenicity of Streptomyces scabiei, the causative agent of common scab in root and tuber crops. Indeed, this enzyme hydrolyzes cellobiose and cellotriose to feed glycolysis with glucose directly and modifies the intracellular concentration of these cello-oligosaccharides, which are the virulence elicitors. The inactivation of bglC led to unexpected phenotypes such as the constitutive overproduction of thaxtomin A, the main virulence determinant of S. scabiei. In this work, we reveal a new target substrate of BglC, the phytoalexin scopolin. Removal of the glucose moiety of scopolin generates scopoletin, a potent inhibitor of thaxtomin A production. The hydrolysis of scopolin by BglC displayed substrate inhibition kinetics, which contrasts with the typical Michaelis–Menten saturation curve previously observed for the degradation of its natural substrate cellobiose. Our work, therefore, reveals that BglC targets both cello-oligosaccharide elicitors emanating from the hosts of S. scabiei, and the scopolin phytoalexin generated by the host defense mechanisms, thereby occupying a key position to fine-tune the production of the main virulence determinant thaxtomin A.

Interactive effect of biocontrol agents in the management of Fusarium rot in cardamom and its impact on plant defense mechanism

Cardamom plantations are subjected to constant threat due to the Fusarium rot disease caused by Fusarium oxysporum Schlecht which is pronounced during summer months. The current study deals with the identification of an effective and ecofriendly management practice for the disease through the use of biocontrol agents. Survey conducted between February and May 2019 revealed maximum disease severity and incidence in Pampadumpara panchayat of Nedumkandam block (84.40% and 100%) and minimum in Erattaar panchayat of Kattappanablock (50.40% and 60.00%). A pot culture experiment was conducted to study the effect of three bioagents (Glomus fasciculatum, Trichoderma asperellum and Pseudomonas fluorescens) individually as well as in combinations. Root inoculation of G. fasciculatum with basal application and spray with P. fluorescens as well as root inoculation of G. fasciculatum along with basal application of T. asperellum and P. fluorescens spray were identifiedto be effective against the disease. Disease suppression by the above bioagents was facilitated by reduced pathogen antagonist ratio in the soil, high level of mycorrhizal colonization in the roots and enhanced biochemical activity of defense enzymes like peroxidase, poly phenol oxidase and phenylalanine ammonia lyase in the plants.

A Mechanistic insight into chemical cues and interactions involved in herbivory induced jasmonate mediated plant defense mechanism

The first step in plant defense mechanism is to sense the insect attack stimulus. Plant sensitivity of an insect attack is the first step of defense. Molecules generated by the oral secretion of the insect interact with the plant receptors to trigger plant defense mechanisms. We selected some highly cited insect elicitors molecules, volicitin, caeliferin, bruchin which interact with plant defense by interacting with plant elicitors (systemin, inceptin and peps) located on the plant cell surface. This interaction activates plant receptors SYR1, LRR, PEPR and triggers downstream defense signaling. The octadecanoid pathways, involving enzymes allene oxide synthase (AOS) and Hydroxyperoxide lyase (HPL) are activated. These enzymes mediate production of green leafy volatiles and Jasmonic acid by interacting with hydroxperoxide molecules. We docked the elicitors with receptors and enzymes with substrates in the pathway of JA production. Phe was found to be an important amino acid that interacts with 13- hydroxyperoxides in the case of AOS to produce JA but not in the case of HPL. JA is converted to JA-Ile which shows strong binding with COI1 and COI1-JA-Ile complex docked with JAZ which showed strong interaction with five hydrogens and one salt bridge bond. AOS and HPL showed less than 40% identity for sequence and structure alignment. AOS and HPL had shown an interaction between each other and showed a common interaction partner of the Lipoxygenase family. HPL shows interaction with ADH2 (Alcohol dehydrogenase) involved in GLVs production. AOS also showed interaction partner AOC, COI1 and OPR1 which are involved in JA-induced plant defense mechanism.

SEED HYDROPRIMING TECHNIQUE IN CEREAL CROPS: A REVIEW

Cereals contribute to 50% of total caloric intake and 95% of the total food requirement globally. Increasing climate change and population has increased the food demand and endangered the productivity of food crops due to various biotic and abiotic stresses and within these conditions’ world is trying to push itself towards increasing the grain yield per unit of land. Several methods of seed priming are practiced to rejuvenate the seeds and remove the environmental stress. Hydro priming, a method of seed priming, has prominent advantage of stresses resistance, better crop stand, and emergence. In order to cope with the future challenges of crop productivity knowledge on the beneficial effects of hydro priming is important. Hydro priming induces DNA repair processes and Antioxidant responses associated as pre-germinative metabolism that leads to early and better seedling growth. Seed Hydro priming may be the best solution to the germination related problems especially in crops grown in unfavorable conditions and enhanced activation of the plant defense mechanism describes this process. Defining the exact treatment duration, water volume, and temperature of water during Hydro priming can revolutionize the farming system with better results.

In silico modelling and characterization of eight blast resistance proteins in resistant and susceptible rice cultivars

Background Nucleotide-binding site-leucine-rich repeat (NBS-LRR) resistance genes are the largest class of plant resistance genes which play an important role in the plant defense response. These genes are better conserved than others and function as a recognition-based immune system in plants through their encoded proteins. Results Here, we report the effect of Magnaporthe oryzae, the rice blast pathogen inoculation in resistant BR2655 and susceptible HR12 rice cultivars. Transcriptomic profiling was carried out to analyze differential gene expression in these two cultivars. A total of eight NBS-LRR uncharacterized resistance proteins (RP1, RP2, RP3, RP4, RP5, RP6, RP7, and RP8) were selected in these two cultivars for in silico modeling. Modeller 9.22 and SWISS-MODEL servers were used for the homology modeling of eight RPs. ProFunc server was utilized for the prediction of secondary structure and function. The CDvist Web server and Interpro scan server detected the motif and domains in eight RPs. Ramachandran plot of eight RPs confirmed that the modeled structures occupied favorable positions. Conclusions From the present study, computational analysis of these eight RPs may afford insights into their role, function, and valuable resource for studying the intricate details of the plant defense mechanism. Furthermore, the identification of resistance proteins is useful for the development of molecular markers linked to resistance genes.

Hypoxic Treatment Decreases the Physiological Action of the Herbicide Imazamox on Pisum sativum Roots

The inhibition of acetolactate synthase (ALS; EC 2.2.1.6), an enzyme located in the biosynthetic pathway of branched-chain amino acids, is the target site of the herbicide imazamox. One of the physiological effects triggered after ALS inhibition is the induction of aerobic ethanol fermentation. The objective of this study was to unravel if fermentation induction is related to the toxicity of the herbicide or if it is a plant defense mechanism. Pea plants were exposed to two different times of hypoxia before herbicide application in order to induce the ethanol fermentation pathway, and the physiological response after herbicide application was evaluated at the level of carbohydrates and amino acid profile. The effects of the herbicide on total soluble sugars and starch accumulation, and changes in specific amino acids (branched-chain, amide, and acidic) were attenuated if plants were subjected to hypoxia before herbicide application. These results suggest that fermentation is a plant defense mechanism that decreases the herbicidal effect.