A distinct member of the basic (class I) chitinase gene family in potato is specifically expressed in epidermal cells

Enhanced resistance to blister blight in transgenic tea (Camellia sinensis [L.] O. Kuntze) by overexpression of class I chitinase gene from potato (Solanum tuberosum)

Tea is the second most consumed beverage in the world. A crop loss of up to 43 % has been reported due to blister blight disease of tea caused by a fungus, Exobasidium vexans. Thus, it directly affects the tea industry qualitatively and quantitatively. Solanum tuberosum class I chitinase gene (AF153195) is a plant pathogenesis-related gene. It was introduced into tea genome via Agrobacterium-mediated transformation with hygromycin phosphotransferase (hpt) gene conferring hygromycin resistance as plant selectable marker. A total of 41 hygromycin resistant plantlets were obtained, and PCR analysis established 12 plantlets confirming about the stable integration of transgene in the plant genome. Real-time PCR detected transgene expression in four transgenic plantlets (T28, C57, C9, and T31). Resistance to biotrophic fungal pathogen, E. vexans, was tested by detached leaf infection assay of greenhouse acclimated plantlets. An inhibitory activity against the fungal pathogen was evident from the detached leaves from the transformants compared with the control. Fungal lesion formed on control plantlet whereas the transgenic plantlets showed resistance to inoculated fungal pathogen by the formation of hypersensitivity reaction area. This result suggests that constitutive expression of the potato class I chitinase gene can be exploited to improve resistance to fungal pathogen, E. vexans, in economical perennial plantation crop like tea.

Brittle culm15 encodes a membrane-associated chitinase-like protein required for cellulose biosynthesis in rice

Plant chitinases, a class of glycosyl hydrolases, participate in various aspects of normal plant growth and development, including cell wall metabolism and disease resistance. The rice (Oryza sativa) genome encodes 37 putative chitinases and chitinase-like proteins. However, none of them has been characterized at the genetic level. In this study, we report the isolation of a brittle culm mutant, bc15, and the map-based cloning of the BC15/OsCTL1 (for chitinase-like1) gene affected in the mutant. The gene encodes the rice chitinase-like protein BC15/OsCTL1. Mutation of BC15/OsCTL1 causes reduced cellulose content and mechanical strength without obvious alterations in plant growth. Bioinformatic analyses indicated that BC15/OsCTL1 is a class II chitinase-like protein that is devoid of both an amino-terminal cysteine-rich domain and the chitinase activity motif H-E-T-T but possesses an amino-terminal transmembrane domain. Biochemical assays demonstrated that BC15/OsCTL1 is a Golgi-localized type II membrane protein that lacks classical chitinase activity. Quantitative real-time polymerase chain reaction and β-glucuronidase activity analyses indicated that BC15/OsCTL1 is ubiquitously expressed. Investigation of the global expression profile of wild-type and bc15 plants, using Illumina RNA sequencing, further suggested a possible mechanism by which BC15/OsCTL1 mediates cellulose biosynthesis and cell wall remodeling. Our findings provide genetic evidence of a role for plant chitinases in cellulose biosynthesis in rice, which appears to differ from their roles as revealed by analysis of Arabidopsis (Arabidopsis thaliana).

Infection with Rhizoctonia solani induces defense genes and systemic resistance in potato sprouts grown without light

Rhizoctonia solani is an important soilborne and seedborne fungal pathogen of potato (Solanum tuberosum). The initial infection of sprouts prior to emergence causes lesions and may be lethal to the sprout or sprout tip, which results in initiation and compensatory growth of new sprouts. They emerge successfully and do not suffer significant damage. The mechanism behind this recovery phenomenon is not known. It was hypothesized that infection may induce pathogen defense in sprouts, which was investigated in the present study. Tubers were sprouted in cool and moist conditions in darkness to mimic conditions beneath soil. The basal portion of the sprout was isolated from the apical portion with a soft plastic collar and inoculated with highly virulent R. solani. Induction of defense-related responses was monitored in the apical portion using microarray and quantitative polymerase chain reaction techniques at 48 and 120 h postinoculation (hpi) and by challenge-inoculation with R. solani in two experiments. Differential expression of 122 and 779 genes, including many well-characterized defense-related genes, was detected at 48 and 120 hpi, respectively. The apical portion of the sprout also expressed resistance which inhibited secondary infection of the sprouts. The observed systemic induction of resistance in sprouts upon infection with virulent R. solani provides novel information about pathogen defense in potato before the plant emerges and becomes photosynthetically active. These results advance our understanding of the little studied subject of pathogen defense in subterranean parts of plants.

In vitro antifungal activity and mechanism of action of chitinase against four plant pathogenic fungi

To determine why chitinase has different antifungal activity on different pathogenic fungi in vitro, we purified recombinant rice chitinase from Pichia pastoris and investigated its antifungal activity against four fungi - Rhizopus stolonifer (Ehrenb. et Fr.) Vuill, Botrytis squamosa Walker, Pythium aphanidermatum (eds.) Fitzp, and Aspergillus niger van Tiegh. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were used to analyze the surface microstructure and proportion of chitin in the cell wall of the four fungi, respectively. The results showed that the chitinase exhibited different antifungal activities against the four fungi, which was directly correlated to the surface microstructure and the proportion of chitin in the fungal cell wall. It will help understanding the antifungal mechanism of the recombinant chitinase and further determining its application scope on crop protection and post-harvest storage of fruits and vegetables.

Promoter activation of pepper class II basic chitinase gene, CAChi2, and enhanced bacterial disease resistance and osmotic stress tolerance in the CAChi2-overexpressing Arabidopsis

The activation of the CAChi2 promoter as the result of bacterial infection and osmotic stresses was examined using the Agrobacterium-mediated transient expression assay. Several stress-related cis-acting elements were revealed within the upstream genomic sequence of the CAChi2 gene. In tobacco leaf tissues transiently transformed with the CAChi2 promoter-beta-glucuronidase (GUS) gene, the CAChi2 promoter was up-regulated by Pseudomonas syringae pv. tabaci infection. The CAChi2-GUS activation was closely related to osmotic stresses, including treatment with mannitol and NaCl. The -378 CAChi2 promoter was sufficient for the CAChi2 gene induction by salicylic acid treatment. CAChi2 overexpression in the transgenic Arabidopsis plants enhanced bacterial disease resistance against Pseudomonas syringae pv. tomato infection. CAChi2-overexpressing Arabidopsis plants also exhibited increased tolerance to NaCl-induced osmotic stresses during seed germination and seedling growth. CAChi2 overexpression induced the expression of the NaCl stress-responsive gene RD29A in the absence of NaCl stress. The CAChi2-overexpressing transgenic plants exhibited increased sensitivity to abscisic acid during seed germination.

Primary structure and tissue-specific expression of the pathogenesis-related protein PR-1b in potatodagger

Summary The infection of potato (Solanum tuberosum) leaves with the late blight pathogen Phytophthora infestans, or treatment with fungal elicitor, leads to the massive accumulation of pathogenesis-related (PR) proteins in the extracellular leaf space. The most abundant of these proteins was purified to apparent homogeneity and identified as a new, basic member of the PR-1 family of defence proteins, designated PR-1b. Antibodies raised against the protein and a cDNA isolated by differential screening were used to study the temporal and spatial patterns of PR-1b protein and mRNA distribution in healthy and infected potato tissues. PR-1b was present in old leaves and at low levels also in the carpels of flowers. In leaves, strong accumulation of PR-1b mRNA and protein occurred in response to infection by the oomycete pathogen Phytophthora infestans or the bacterial pathogen Pseudomonas syringae pv. maculicola. PR-1b mRNA and protein accumulation was clearly initiated at the infection site, but a delayed and sustained accumulation was also observed in neighbouring, uninfected leaves of potato plants. Tissue- and cell type-specific expression of PR-1b was analysed by immunohistochemical and in situ RNA hybridization techniques. Appreciable amounts of PR-1b protein and mRNA were localized in epidermal cells, guard cells of the stomata, glandular trichomes, crystal idioblasts, and cells of the vascular system of infected leaves. However, no significant differences in the amounts and distribution patterns of PR-1b could be observed between compatible and incompatible interactions of potato and Phytophthora infestans, indicating that PR-1b expression is not involved in determining cultivar/race-specific resistance in potato.

Two differentially regulated class II chitinases from parsley

Two distinct cDNA clones, PcCHI1 and PcCHI2, with high sequence similarity to plant chitinases were isolated from parsley (Petroselinum crispum), expressed in Escherichia coli, and the encoded proteins functionally identified as endochitinases. Different expression patterns of the corresponding mRNAs and proteins in infected and uninfected parsley plants indicated distinct roles of the two isoforms in both pathogen defense and plant development. Infection of parsley leaf buds with Phytophthora sojae resulted in the rapid, transient and highly localized accumulation of PcCHI1 mRNA and protein around infection sites, whereas PcCHI2 mRNA and protein were systemically induced at later infection stages. Similar differences in the timing of induction were observed in elicitor-treated, suspension-cultured parsley cells. In uninfected plants, PcCHI1 mRNA was particularly abundant in the transmitting tract of healthy flowers, suggesting a role in the constitutive protection of susceptible transmitting tissue of the style against pathogen ingress and/or in the fertilization process, possibly by affecting pollen tube growth. Localization of PcCHI2 mRNA and protein in the parenchymatic collenchyme of young pedicels may indicate a function in the constitutive protection of this tissue. In addition to such distinct roles of PcCHI1 and PcCHI2 in preformed and induced pathogen defense, both chitinases may have endogenous regulatory functions in plant development.

Chitinolytic enzymes: an exploration

Chitin and chitinolytic enzymes are gaining importance for their biotechnological applications. Particularly, chitinases are used in agriculture to control plant pathogens. Chitinases and chitooligomers produced by enzymatic hydrolysis of chitin can also be used in human health care. The success in employing chitinases for different aspects depends on the supply of highly active preparations at reasonable cost. Therefore, the understanding of biochemistry and genetics of chitinolytic enzymes, their phylogenetic relationships and methods of estimation will make them more useful in a variety of processes in near future.