Study on Exogenous Ethylene Induced Rice Resistance to Rhizoctonia solani

Rice sheath blight is one of the main diseases in rice production in China,which can make rice unable to absorb and utilize nutrients,and has a serious impact on rice yield and quality.In this study,exogenous ethylene was used to induce rice resistance against rice sheath blight,aiming at exploring a new environment-friendly control method of rice sheath blight.The results showed that within a range of certain concentrations,ethylene had no significant effects on mycelium growth,but it could induce resistance to sheath blight in rice.The optimum concentration was 0.2 mmol•L^(-1) and the relative control was 86.17%.It was found that ethylene could effectively increase the activities of peroxidase(POD),phenylalanine ammonia-lyase(PAL),β-1,3-glucanase and reduce the contents of malondialdehyde(MDA),which could enhance the resistance of rice against Rhizoctonia solani.In addition,qRT-PCR detected the expressions of rice defense genes,which indicated that the expressions of the POX,PAL and OsPR1b genes were up-regulated.

Comparative Study of Disease Suppression on Various Host Plants by <i>Bacillus</i>Cyclic Lipopeptides

In biological controls using Bacillus spp., cyclic lipopeptides play a role as elicitors to induce disease resistance on various host plants. However, it is still unclear the specificity between cyclic lipopeptides and host plants to induce disease resistance. In this study, we aimed to clarify the specificity to induce disease resistance among cyclic lipopeptides on various host plants. Our data clearly showed both cyclic lipopeptides conferred disease suppression on most of host plants, but at different range of cyclic lipopeptide concentration. Our findings contribute to understanding the complex on the specificity of cyclic lipopeptide derived induced disease resistance.

Epsilon-poly-L-lysine increases disease resistance of citrus against postharvest green mold by activating amino acid metabolism and phenolic comnpounds biosynthesis

As a famous fruit worldwide,citrus is susceptible to green mold caused by Penicillium digitatum,which causes large economic losses every year.e-Poly-L-lysine(e-PL)is a novel preservative with strong inhibitory effects on fungi,and has the capacity to induce disease resistance in fruit,but the mechanism has been reported rarely,especially in citrus.In the present study,8ooμg/mL e-PL and P digitatum spores were inoculated in two different wounds on the citrus pericarp at an interval of 24 h.The results revealed that e-PL inhibited that the development of green mold without direct contact with P digitatum,indicating that the disease resistance of citrus was activated.Transcriptome analysis revealed that e-PL activated amino acid metabolism and phenylpropanoid biosynthesis.Besides,the accumulation of glutamic acid,proline,arginine,serine,lysine,phenylalanine,and tyrosine were changed during storage.In phenylpropanoid biosynthesis,-PL increased phenylalanine ammonia-lyase(PAL),cinnamate 4-hydroxylase(C4H),and 4-coumarate:coenzyme A ligase(4CL)activities and total phenolic and flavonoid contents.Importantly.among these phenolic compounds,e-PL promoted the accumulation of individual phenolic compounds including ferulic acid,chlorogenic acid,p-coumaric acid,caffeic acid,gallic acid,catechins,epicatechin,and narirutin.In conclusion,e-PL enhanced the resistance of citrus through amino acid metabolism and accumulation of phenolic compounds.These results improved the knowledge of the mechanism of-PL-induced disease resistance and provided a fresh theoretical basis for the use of e-PL in postharvest citrus preservation.

Proteomic study of three component interactions: plant, pathogens and antagonistic fungi

The molecular factors involved in the three-way interaction between plant, pathogenic fungi and antagonistic/biocontrol fungi, such as Trichoderma, are still poorly understood, even if they represent a matter of interest for improving crop management and developing new strategies for plant diseases control. The aim of this work is to investigate the components involved in this interaction and, for this purpose, a proteomic approach was used. 2-D maps of the protein extracts from the single components in various interactions between plants (potato, bean, tobacco or tomato), pathogens (Botrytis cinerea, Rhizoctonia solani or Pythium ultimum) and biocontrol fungi (Trichoderma atroviride strain P1 or Trichoderma harzianum strain T22) were obtained. The proteome of each partner was collected separately and extracted by acetone precipitation in presence of trichloroacetic acid and a reducing agent (DTT). The extracted proteins were separated by isoelectrofocusing (IEF), using IPG (Immobilized pH gradient) strips, followed by SDS-PAGE. In order to improve resolution the separations were performed both on wide than narrow pH range and on different gel lengths. Differential spots were noted in the proteome of the three-way interaction when compared to each single component. These were further characterized by mass spectrometry and in silico analysis with the aim of identifying and cloning the relative genes. During the in vitro interaction of T. harzianum strain T22 with tomato and the culture filtrate or cell walls of pathogens, the spot number was higher than in the presence of pathogen biomass. In terms of Trichoderma differential proteins displayed on 2D gels, the most important changes were obtained in the presence of P. ultimum . During the in vivo interaction with tomato, the antagonist proteome changed much more in presence of soilborne fungi R. solani and P. ultimum than with the foliar fungus B. cinerea, both in terms of total and increased or novel spots. In silico analysis of some of those spots revealed homology with intracellular enzymes (GTPases, hydrolases) and with stress-related proteins (heat shock proteins HSP70, bacteriocin cloacin). Specific proteins in the plant proteome, i.e. pathogenesis-related proteins, have been identified during the in vivo interaction of bean with R. solani and T. atroviride strain P1. This is in agreement with the demonstrated ability of these beneficial fungi to induce plant systemic disease resistance by activating expression of defence-related genes. Proteins extracted from T. atrovride strain P1 which were analysed by mass spectrometry, revealed some interesting homologies with a fungal hydrophobin of Pleurotus ostreatus and an ABC transporter of Ralstonia metallidurans. These could represent molecular factors involved in the antagonistic mechanisms of Trichoderma and play a role in the three-way interaction with the plant and other microbes.

Molecular Basis of Transfer of Induced Resistance in Plants

Two brown spot disease resistant varieties of tobacco, named NC89 V1 and NC89 V2, were obtained by first inducing from disease sensitive NC89 with the two hypovirulent viruses ToMV N14 and CMV SV52, then tissue culturing the plants and finally seed breeding. The disease resistance for both varieties was verified to be stable in three generations. The transcription activities of five plant defense response genes, pr 1a, chi, chs, pal, and lox, in NC89, NC89 V1, and NC89 V2 were studied through RNA blot hybridization. Genome DNA structural differences among the three tobacco lines were identified using randomly amplified polymorphic DNA(RAPD).