Effects Of Pathogenic Bacterium On Activities Of Lignin-related Enzymes And Genes Expressions Of CmCADs And The Possible Defense Pathway In Oriental Melon (Cucumis Melo Var. Makuwa Makino)

Cinnamyl alcohol dehydrogenase(CAD, EC 1.1.1.195)belong to alcohol dehydrogenase gene superfamily which also contain alcohol dehydrogenase subfamily (ADH, EC 1.1.1.1) and formaldehyde dehydrogenase FDH, EC 1.2.1.1).CAD can synthesize coniferyl alcohol、sinapyl alcohol and p-coumaryl alcohol precursors in lignin biosynthesis and be indudeced by pathogenic bacteria infection to build the plant defense system. At present, we have identified 5 CAD genes in the melon genome and cloned 4 CAD genens of them but without knowing their physiologicaland biochemical functions. We analysed the expression of the CmCADs in the leaves of the’Caihong7’which were infected by suffered from powdery mildew and fusarium wilt and ’Yumeiren’ which were infected by fusarium wilt through natural occurrence to explore their response to the pathogen infection.To explore the response further we measured related physiology indexes of resistance stress, lingin content, activities of lingin-related enzymes, genes expressions of CmCADs, fusarium wilt resistance gene FOM-2, phenylalanine ammonia-lyase gene (PAL), peroxidase gene (POD) and SA content in the vegetative organs of ’Caihong7’ seedlings after different days inoculated by fusarium wilt. The main research results were listed as follows:1. Phylogenetic tree of the five CAD genes in melon and CADs participating in defense response in other plants showed that CmCADl and CmCAD2 had more relationship with AtCAD4 and CmCAD5 from arabidopsis. CmCAD3 had a high homology with BdCADl from brachypodium distachyon and CsCAD6 from cucumis sativus. CmCAD4 was in the same class with AtCADl and OsCAD4 from oryzasativa,while CmCAD5 was in the same class with AtCAD2,AtCAD3.As AtCAD4,AtCAD5 and BdCADl related to lignin synthesis and AtCAD2, AtCAD3 participated in defense response to stress, so we suggested that the five melon CAD genes might played different roles and are more likely to function in defense fusarium wilt.2. Promoter analysis of the five genes revealed that the five genes all possess motif TC-rich repeats which are involved in response to defence response and adversity stress.In the same time, CmCADl has TCA-element involved in response to salicylic acid and TGA involved in response to auxin and CmCAD2 has GARE elememnt involved in response to gibberellin. CmCAD3 and CmCADS are both have fngal elicitor responsive element Box-W1. CmCAD4 posesses TCA-element which response to salicylic acid, GARE-mitif which response to gibberellin and ERE which response to ethylene. The resules suggested that the CmCADs may response to diiferent stresses and gived support to further explore their specific functions.3. The results of expression in leaves infected through natural occurrence showed that all the five CmCADs were induced by fusarium wilt in’Caihong7’with 32 and 21 times higher in CmCAD3 and CmCADS respectively compared to conditions. CmCADl was induced by fusarium wilt in ’Yumeiren’ while CmCAD3 was induced by powder mildew in ’Caihong7’.4. The analysis of related physiology indexes as root vigor, electrolyte leakge rate, chlorophyll fluorescence parameters suggested that the roots, cell membrance and photosynthesis wre all damaged after inoculation with fusarium wilt.5. The analysis of lingin content, activities of lingin-related enzymes showed that compared to the control, lingin content, the activities of PAL, POD and CAD in roots, stems and leaves were all improved to varying degrees after inoculation with fusarium wilt.6. The expression of CmCADs indicated that except for the stems, there were existing different members in CAD gene family which were induced after inoculation with fusarium wilt in roots and leaves. 7. The expression of PAL, POD and fusarium wilt resistance gene FOM-2 showed that the expression quantity of PAL and POD kept increasing after inoculation with fusarium wilt in roots and leaves while the expression quantity of FOM-2 showed no significant change both in roots and leaves.8. The content of SA increased significantly both in roots and leaves with positively correlated with inoculation time.In summery, the results suggest that the CmCADs responsed to the pathogenic bacteria infection. Lignin was involved in the process to defend against the fusarium wilt.There were tissue-specific and member-specific fashion for CmCADs to response to the fusarium wilt. Lignification and SA defensive signal pathways may participate in defense response to the fusarium wilt. The data generated in this study will be helpful in procaryotic expression and transgenic experiment to identify the function of CmCADs in response to pathogenic bacteria infection.precise.