On some biochemical physiognomies of two common Darjeeling tea cultivars in relation to blister blight disease

Abstract

Tea, Camellia sinensis (L.) O. Kuntze, an agro-based industry, is considered as one of the prime sector of exporting resources and thus considered as “cash-crop”. Earlier report shows that tea is native to eastern and northern India, which was cultivated and consumed there since long back. Presently, more scientific reports confirmed the health-benefit traits of tea and awareness increased to a greater extent and in this regard, tea has gained its best worldwide popularity. Darjeeling Tea attained its highest acceptance globally for its pre-eminence in flavour, colour and taste and thus crop improvement is the prime interest to the Indian Scientific Community. Blister blight disease, a common disorder of tea bushes (Exobasidium vexans, a Basidiomycetes fungus) causes drastic damage of tea plantation. Depending on quality production, two common cultivars were released by TRA, Jorhat, Assam viz. Bannockburn – 157 (B-157) and Ambei Valai - 2 (AV-2), of which B-157 is susceptible to the Blister Blight and AV-2 is fairly resistant cultivar. Some biochemical considerations between the two cultivars have been made here for understanding the biochemical reasons behind the resistant characteristics. Plant secondary metabolites, like total phenol, proanthocynadin, total soluble protein provide defending feature against disease onset. AV-2 cultivar shows advantage over B-157 in these regard. Depending on band intensity analysis of native gels, acid phosphatase, catechol oxidase, peroxidase and superoxide dismutase occur in superior amount in AV-2 cultivar than that of B-157. The specific role of these enzymes in blister blight disease compatibility of two cultivars studied has been discussed.     

Temperature‐dependent regulation of the Ochrobactrum anthropi proteome

Ochrobactrum anthropi is a Gram‐negative rod belonging to the Brucellaceae family, able to colonize a variety of environments, and actually reported as a human opportunistic pathogen. Despite its low virulence, the bacterium causes a growing number of hospital‐acquired infections mainly, but not exclusively, in immunocompromised patients. The aim of this study was to obtain an overview of the global proteome changes occurring in O. anthropi in response to different growth temperatures, in order to achieve a major understanding of the mechanisms by which the bacterium adapts to different habitats and to identify some potential virulence factors. Combined quantitative mass spectrometry‐based proteomics and bioinformatics approaches were carried out on two O. anthropi strains grown at temperatures miming soil/plants habitat (25°C) and human host environment (37°C), respectively. Proteomic analysis led to the identification of over 150 differentially expressed proteins in both strains, out of over 1200 total protein identifications. Among them, proteins responsible for heat shock response (DnaK, GrpE), motility (FliC, FlgG, FlgE), and putative virulence factors (TolB) were identified. The study represents the first quantitative proteomic analysis of O. anthropi performed by high‐resolution quantitative mass spectrometry.     

Species‐specific elicitors induce tea leaf to arrest the endoparasitoid Ascogaster reticulata (Hymenoptera: Braconidae)

Ascogaster reticulata Watanabe (Hymenoptera: Braconidae) is an egg‐larval endoparasitoid of the smaller tea tortrix, Adoxophyes honmai Yasuda. Recent studies have examined tritrophic interactions among Camellia sinensis, A. honmai and A. reticulata, but the effect of non‐host insects on the induction of tea plant that may affect foraging behaviour of A. reticulata remains unclear. In this study, we selected two non‐host insects, Homona magnanima Diakonoff and Ostrinia furnacalis (Guenée), as representative species in our bioassays. Tea leaves were treated with homogenized female reproductive tissues of a non‐host insect in comparison with untreated leaves in a choice test. Residence times of parasitoids on both leaves were recorded. The parasitoids seemed to prefer walking on leaves treated with homogenates of H. magnanima over untreated leaves, but the difference in residence times was not significant. In contrast, its residence time on leaves treated with homogenates of O. furnacalis was significantly shorter than that on untreated leaves. Thus, the induction of tea leaf surface chemicals may differ among moth species, which may produce different types of elicitors. This difference may, in turn, affect the host‐searching behaviour of A. reticulata.     

Life‐history strategy defends against disease and may select against physiological resistance

Host ecological traits may limit exposure to infectious disease, thereby generating the wide variation in disease incidence observed between host populations or species. The exclusion of disease by ecological traits may then allow selection to act against physiological defenses when they are costly to maintain in the absence of disease. This study investigates ecological resistance in the Silene-Microbotryum pathosystem. An estimated 80% of perennial Silene species host the anther-smut disease while no annuals harbor the disease in nature. Artificial inoculations of annual and perennial Silene plants, obtained from both natural and horticultural populations, demonstrate that the absence of disease in annuals is not explained by elevated physiological resistance. The annual habit is thus a powerful form of ecological defense against anther smut. Moreover, the higher susceptibility of annual species to anther smut relative to perennials supports the hypothesis of a loss of costly physiological resistance under ecological protection. The observation in annuals that physiological susceptibility is correlated with lower rates of flowering (i.e., lower fitness) suggests that variation in physiological resistance is costly in the absence of disease, even in a naїve Silene species. The absence of disease in natural populations of annuals combined with their high physiological susceptibility attest to the strength of host ecology in shaping the distribution of disease and to the dynamic nature of disease resistance.     

Arbuscular mycorrhiza‐mediated resistance in tomato against Cladosporium fulvum‐induced mould disease

Root colonization with arbuscular mycorrhizal fungi (AMF) enhances plant resistance particularly against soil‐borne pathogenic fungi. In this study, mycorrhizal inoculation with Glomus mosseae (Gm) significantly alleviated tomato mould disease caused by the air‐borne fungal pathogen, Cladosporium fulvum (Cf). The disease index (DI) in local leaves (receiving pathogen inoculation) and systemic leaves (just above the local leaf without pathogen inoculation) was 36.4% and 11.7% in mycorrhizal plants, respectively, whereas DI was 59.6% and 36.4% in the corresponding leaves of AMF non‐inoculated plants, after 50 days of Gm inoculation, corresponding to 15 days after Cf inoculation by leaf infiltration. Foliar spray inoculation with Cf also revealed that AMF pre‐inoculated plants had a higher resistance against subsequent pathogen infection, where the DI was 41.3% in mycorrhizal plants vs. 64.4% in AMF non‐inoculated plants. AMF‐inoculated plants showed significantly higher fresh and dry weight than non‐inoculated plants under both control (without pathogen) and pathogen treatments. AMF‐inoculated plants exhibited significant increases in activities of superoxide dismutase and peroxidase, along with decreases in levels of H₂O₂ and malondialdehyde, compared with non‐inoculated plants after pathogen inoculation. AMF inoculation led to increases in total chlorophyll contents and net photosynthesis rate as compared with non‐inoculated plants under control and pathogen infection. Pathogen infection on AMF non‐inoculated plants led to decreases in chlorophyll fluorescence parameters. However, pathogen infection did not affect these parameters in mycorrhizal plants. Taken together, these results indicate that AMF colonization may play an important role in plant resistance against air‐borne pathogen infection by maintaining redox poise and photosynthetic activity.     

BID‐dependent release of mitochondrial SMAC dampens XIAP‐mediated immunity against Shigella

The X‐linked inhibitor of apoptosis protein (XIAP) is a potent caspase inhibitor, best known for its anti‐apoptotic function in cancer. During apoptosis, XIAP is antagonized by SMAC, which is released from the mitochondria upon caspase‐mediated activation of BID. Recent studies suggest that XIAP is involved in immune signaling. Here, we explore XIAP as an important mediator of an immune response against the enteroinvasive bacterium Shigella flexneri, both in vitro and in vivo. Our data demonstrate for the first time that Shigella evades the XIAP‐mediated immune response by inducing the BID‐dependent release of SMAC from the mitochondria. Unlike apoptotic stimuli, Shigella activates the calpain‐dependent cleavage of BID to trigger the release of SMAC, which antagonizes the inflammatory action of XIAP without inducing apoptosis. Our results demonstrate how the cellular death machinery can be subverted by an invasive pathogen to ensure bacterial colonization.     

侧孢芽孢杆菌Bl13对番茄早疫病防治效果及机制

以对番茄早疫病原菌有良好拮抗效果的侧孢芽孢杆菌Bl13为研究对象,采用盆栽试验,通过测定番茄株高、茎粗、番茄早疫病病情指数、叶片内防御酶活性以及根区土壤微生物多样性、微生物群落结构组成等指标,探究侧孢芽孢杆菌Bl13防治番茄早疫病的效果及机制。结果表明: 接种Bl13可显著降低番茄早疫病的病情指数,提高叶片内多酚氧化酶(PPO)、过氧化物酶(POD)等防御酶活性,降低病害对植物地上部分及根系生长发育的影响。同时,改善番茄根区土壤微生物群落结构,使芽孢杆菌属、假单胞菌属等常见有益菌属相对丰度显著提高,油壶菌属、血赤壳属相对丰度显著降低。侧孢芽孢杆菌Bl13可通过提高番茄叶片内防御酶活性并增加根区中有益微生物的数量来增强植物对番茄早疫病的抗性,从而实现对番茄早疫病的防治。     

Mitochondrial peroxiredoxin‐5 as potential modulator of mitochondria‐ER crosstalk in MPP+‐induced cell death

Peroxiredoxin‐5 (PRDX5) is an antioxidant enzyme which differs from the other peroxiredoxins with regards to its enzymatic mechanism, its high affinity for organic peroxides and peroxynitrite and its wide subcellular distribution. In particular, the mitochondrial isoform of PRDX5 confers a remarkable cytoprotection toward oxidative stress to mammalian cells. Mitochondrial dysfunction and disruption of Ca²⁺ homeostasis are implicated in neurodegeneration. Growing evidence supports that endoplasmic reticulum (ER) could operate in tandem with mitochondria to regulate intracellular Ca²⁺ fluxes in neurodegenerative processes. Here, we overexpressed mitochondrial PRDX5 in SH‐SY5Y cells to dissect the role of this enzyme in 1‐methyl‐4‐phenylpyridinium (MPP)⁺‐induced cell death. Our data show that mitochondria‐dependent apoptosis triggered by MPP⁺, assessed by the measurement of caspase‐9 activation and mitochondrial DNA damage, is prevented by mitochondrial PRDX5 overexpression. Moreover, PRDX5 overexpression blocks the increase in intracellular Ca²⁺, Ca²⁺‐dependent activation of calpains and Bax cleavage. Finally, using Ca²⁺ channel inhibitors (Nimodipine, Dantrolene and 2‐APB), we show that Ca²⁺ release arises essentially from ER stores through 1,4,5‐inositol‐trisphosphate receptors (IP₃R). Altogether, our results suggest that the MPP⁺ mitochondrial pathway of apoptosis is regulated by mitochondrial PRDX5 in a process that could involve redox modulation of Ca²⁺ transporters via a crosstalk between mitochondria and ER.     

Greek indigenous streptomycetes as biocontrol agents against the soil‐borne fungal plant pathogen Rhizoctonia solani

Aims

To examine the biocontrol potential of multiactive Greek indigenous Streptomyces isolates carrying antifungal activity against Rhizoctonia solani that causes damping‐off symptoms on beans.

Methods and Results

A total of 605 Streptomyces isolates originated from 12 diverse Greek habitats were screened for antifungal activity against R. solani DSM843. Almost one‐third of the isolates proved to be antagonistic against the fungus. From the above isolates, six were selected due to their higher antifungal activity, identified by analysing their 16S rRNA gene sequence and studied further. The obtained data showed the following: firstly, the isolates ACTA1383 and ACTA1557 exhibited the highest antagonistic activity, and therefore, they were selected for in vivo experiments using bean seeds as target; secondly, in solid and liquid culture experiments under optimum antagonistic conditions, the medium extracts from the isolates OL80, ACTA1523, ACTA1551 and ACTA1522 suppressed the growth of the fungal mycelium, while extracts from ACTA 1383 and ACTA1557 did not show any activity.

Conclusions

These results corresponded important indications for the utility of two Greek indigenous Streptomyces isolates (ACTA1557 and ACTA1383) for the protection of the bean crops from R. solani damping‐off symptoms, while four of them (isolates OL80, ACTA1523, ACTA1551 and ACTA1522) seem to be promising producers of antifungal metabolites.

Significance and Impact of the Study

This is the first study on the biocontrol of R. solani using multiactive Streptomyces isolates originated from ecophysiologically special Greek habitats. Our study provides basic information to further explore managing strategies to control this critical disease.