Response Of Rice Leaves Cell Wall To Magnaporthe Oryzae Infection At Seedling Stage

Rice is a crop of global importance.In terms of yield losses,the most serious disease of rice is blast caused by the ascomycete fungus Magnaporthe oryzae.Due to the global agronomic importance of rice,an improved understanding of the molecular basis of the interaction between M.oryzae and its host is of particular significance.Such information offers the promise of new and durable disease control strategies,and improved breeding methodologies.Furthermore,the interaction between rice and M.oryzae is considered to be a model system with which to study plant-pathogen interactions.The plant cell wall plays an important role in the basal defense response against pathogenic attack and acts as the ‘frontline' of the plant defense system.However,to date,the role of the plant cell wall in the basal defense response to M.oryzae infection has not been widely studied.Among the responses of living plant cells to fungal attack,the formation of cell wall appositions is one of the most common.But,changes to the molecular structure and composition of rice cell wall which may occur during infection by M.oryzae has not been systematically studied.In light of which,the systematic research was conducted on the cell wall response of rice leaves to M.oryzae infection at seedling stage.From these studies the following results were obtained:1.The role of autofluorescence enhancement in different rice varieties during M.oryzae infection.Autofluorescence enhancement of rice leaves was observed and measured during M.oryzae infection.Changes in autofluorescence were observed in both resistant and susceptible rice varieties.This enhancement appeared faster in resistant varieties compared to susceptible variety.The autofluorescenc in resistant varieties was significantly stronger than in the susceptible variety.The response of rice leaves to M.oryzae infection was systematic.The mesophyll was the tissue with the strongest observed response to M.oryzae infection.These data demonstrated that cell wall autofluorescence enhancement of rice leaves was associated with rice resistance to M.oryzae infection.Important information about changes of rice cell wall appositions during M.oryzae attack could obtained through autofluorescence signal detection.2.Distribution of cell wall-associated epitopes in different rice leaf substructures.A panel of 24 antibodies which recognize a range of cell wall-associated epitopes were used to probe transverse sections of rice leaves.11 antibodies belong 4kinds could label rice leaves effectively.The abundance and distribution of cellulose,lignin,mannan,homogalaturonan epitopes with different levels of methyl esterification,arabinan,galactan,arabinogalactan proteins and extensin in upper and lower epidermis,mesophyll cell,motor cell,vascular bundles sheath,zylem,phloem,upper and lower sclerenchyma were elucidated.The results provided the basis for illuminating the function of different rice leaf substructures.3.The response of rice cell wall composition to infection with M.oryzaeThe composition changes of rice leaf cell wall during compatible and incompatible interactions were investigated at seedling stage via immunocytochemistry and immune gold labelling using a panel of anti-cell wall antibodies.The results showed that mesophyll cell,epidermis,motor cell,vascular bundles sheath and vascular could take part in rice-M.oryzae interaction.The content of arabinogalactan proteins,mannan and pectin in cell-wall of rice leaves was associated with rice resistance.The abundance of arabinogalactan proteins epitopes labeled by JIM13 increased significantly during M.oryzae infection.The stronger resistance of rice variety was,the faster of arabinogalactan proteins content increased and the greater the increase during 24hpi-72 hpi.In relation to changes observed in mannan containing epitopes recognized by the anti-mannan antisera,infection with M.oryzae led to a gradual decrease in mannan containing epitopes in the tissues labelled during early infection stage.The expression of the mannanepitopes in the mesophyll was closely associated with the resistance of the rice variety to blast fungus.The stronger the resistance of the variety,the higher content of mannan in mesophyll cell.The response of different pectic polysaccharides to M.oryzae infection were different.The content of arabinan(LM6)and heavily methyl esterified homogalacturonan(JIM7)epitopes were significantly decreased,but galactanepitopes(LM5)increased during M.oryzae infection.Theresults showed that the content of arabinogalactan protein,mannan and pectin was closely related to rice resistance.4.The response of cell wall associated gene expression to infection with M.oryzaeThe expression of cell wall associated genes of rice leaves in both susceptible(LTH)and resistant(YJG19 and IRBL22)rice varieties were detected during M.oryzae infection.The results showed that seven cell wall-associated kinase genes could reponse to M.oryzae infection.The stronger the resistance of the rice variety,the faster the induction of the cell wall-associated kinase genes,and the shorter the time period required for elevation of expression to high levels.The expression of twelve genes associated with mannan biosynthesis,were also examined.The expression of all of which was shown to respond to M.oryzae infection.The expression trends of 4 genes were very different between resistant and susceptible varieties.The expression peaks of 6 genes were significantly higher in resistance varieties than in susceptible variety.The expression level of 2 genes was significantly higher in resistance varieties than in susceptible variety at 0hpi.Five genes encoding for arabinogalactan proteins were shown to respond to M.oryzae infection.The expression peak of these genes all occurred at 24 hpi in YJ19 and the level of expression were significantly higher in YJ19 than in RIBL22 and LTH.The trend of genes expression in IRBL22 was similar to YJ19.M.oryzae infection caused the expression of arabinogalactan proteins encoding genes in LTH declined significantly.The expression peak in LTH appeared during 0hpi-12 hpi then the expression level reduced quickly.These results showed that cell wall associated gene expression could response to infection with M.oryzae.The reponse speed,expression maximum and expression trend of cell wall associated genes were related to rice resistance.The main innovation points of this research were as follows:The autofluorescence enhancement phenomenon during M.oryzae infection was researched systemically.The systematic response of rice leaves to M.oryzae infection was found through the study about different rice substructures.The cell wall compositions and reponse of different substructures of rice leaves were researched for the first time.In conclusion,the autofluorescence enhancement of rice leaf cell wall was detected.It was cleared that cell wall autofluorescence enhancement of rice leaves was associated with rice resistance.The response of rice leaves to M.oryzae infection was systematic.The mesophyll was the tissue with strongest reponse to M.oryzae infection.The epidermis,motor cell,vascular bundles sheath and vascular were involved in rice-M.oryzae interaction.The distribution characteristic ofcellulose,lignin,mannan,homogalaturonan epitopes with different levels of methyl esterification,arabinan,galactan,arabinogalactan proteins and extensin in different substructures was clarified.The content of arabinogalactan proteins,mannan and pectin was closely related to rice resistance.The reponse speed,expression maximum and expression trend of cell wall associated genes were related to rice resistance.