Riclinoctaose Induces Plant Resistance Response And Its Application

As a kind of plant elicitor,biological oligosaccharide plays an important role in the large-scale use of replacing chemical pesticides.It has attracted more and more attention due to its rich raw materials and environmental pollution-free characteristics.Succinyl glycan is an extracellular polysaccharide secreted by Agrobacterium and Rhizobacteria.After enzymatic hydrolysis by succinyl glycan depolymerase,a homogeneous oligosaccharide composed of seven glucose and one galactose,Riclinoctaose（RiOc）is obtained.This paper mainly studies the application of RiOc as a new type of plant elicitor in inducing and improving plant disease resistance,and explores its induction mechanism and application prospect.The main findings are as follows:1.Screening and identification of crop species for which RiOc can induce resistance.Using RiOc as an elicitor,its ability to activate defense responses of 30 major food and commercial crops was determined,and it was found that the responses of plants to RiOc were species-specific.Among them,RiOc has a good induction effect on the defense response of Solanaceae,Gramineae and Legumes,while its effect on Cruciferae is not obvious.And the effect of RiOc is dose-dependent with plants.After short-term treatment（10 min）,the content of hydrogen peroxide in leaves of 15 plants with low concentration（50 mg/L）of RiOc increased significantly compared with the control group,and 16 kinds of plants with high concentration（500 mg/L）of RiOc increased significantly;After long-term treatment（30 min）,9 plants with low concentration RiOc increased significantly,and 14 plants with high concentration RiOc increased significantly.The infection experiment was used to verify the actual disease resistance effect of some plants.It was found that RiOc could enhance the resistance of potato to Phytophthora infestans and wheat to Fusarium graminearum.2.The signaling pathway of RiOc-induced potato resistance was studied.Late blight caused potato yield decline,and potato is the fourth largest economic crop in the world,so potato was chosen as the research object to explore its disease resistance mechanism.The results showed that RiOc induced the increase of reactive oxygen species and reactive nitrogen content in potato leaves in a dose-dependent manner.When the RiOc concentration reached200μg/m L and 500μg/m L,the H₂O₂ and NO contents reached their peaks and remained stable,respectively.Transcriptome analysis indicated that RiOc may activate salicylic acid-mediated defense responses in potato cells through the pattern recognition receptor LYK3,while enhancing the photosynthetic capacity of leaf cells.Metabolome analysis showed that the primary metabolism of cells was enhanced in the early stage（24 h）of RiOc induction,and the secondary metabolism of cells was enhanced in the later stage（72 h）of induction.And after RiOc treatment,the activities of various resistance-related enzymes in cells were enhanced.3.Discovered the pattern recognition receptor LYK3 that recognizes RiOc on the surface of potato cells.Fluorescence microscopy imaging showed that RiOc could attach to the surface of potato protoplasts.Molecular docking analysis shows that the binding ability of RiOc to LYK3 is better than that of other 26 possible pattern recognition receptors.All monosaccharide units of RiOc are involved in the binding of LYK3,and the non-reducing end contains pyruvyl glucose and the reducing end of the galactose shows more binding sites.The extracellular region of LYK3 in potato was heterologously expressed by Pichia pastoris,and the fragment size was 659 bp.The binding experiment of isothermal titration calorimetry（ITC）showed that RiOc had strong binding ability to LYK3,withΔH of-32.9 k J/mol.The significant changes confirm that hydrogen bonds play an important role in their binding in molecular docking analysis.4.It was found that RiOc can balance the defense and growth of potato roots.RiOc（concentrations of 50 mg/L and 200 mg/L）was added to the medium of potato tissue culture seedlings to monitor the growth,development and metabolic transcription of potato roots from the second to the fifth week.The results showed that RiOc induced an increase in the activity of resistance-related proteins in potato root tissue,an up-regulation of MPK3/6 and its downstream salicylic acid-mediated defense response-related gene transcription,and induced auxin signaling pathway-related genes and transcription.Up-regulation of factor transcription in a dose-and time-dependent manner.Metabolome analysis showed that the content of intracellular by-products such as acetic acid decreased after RiOc induction,and the root tissue had more reasonable resource allocation and enhanced stress tolerance.And after RiOc treatment,the number and fresh weight of adventitious roots of potato tissue culture surface increased significantly,showing a good promoting effect on root growth.5.The field experiment of RiOc on potato disease resistance was carried out.Potato leaves were sprayed with RiOc regularly in the field,and their growth changes were recorded.The results showed that the plant height and stem diameter of potato could be increased by up to10.59%and 9.75%after spraying RiOc,and RiOc increased the average number of leaves and average leaf surface area of potato.The statistics of leaf lesions showed that RiOc could significantly improve the resistance of potato to pathogenic bacteria,and with the increase of RiOc concentration,the disease resistance of potato also increased,and the inhibition efficiency reached 64.71%.The quality distribution and yield statistics of potato seed potatoes showed that RiOc affected the quality distribution of potato seed potatoes.The number of seed potatoes with a weight of more than 4 g after RiOc treatment was significantly higher than that of the control group,up to 21.12%.And RiOc treatment can significantly increase the yield of potato seed potatoes,up to 12.16%.Conclusion:RiOc can induce resistance in many crops such as potato.In potato,RiOc is realized by sensing the pattern recognition receptor LYK3 on the potato cell surface and enhancing signaling pathways such as salicylic acid.RiOc can also promote the growth and development of potato roots.The field experiment results showed that RiOc significantly improved the disease resistance of potato.