Mechanism Of Red Light Enhancing Rhizosphere Colonization Of The Rhizosphere Promoting Bacterium Serratia Plymuthica A21-4 In Tomato

The instability of plant mycorrhizal colonization ability is a major problem that restricts the effective and sustainable development of plant mycorrhizal promoting bacteria in agricultural production.Photoquality can affect the synthesis and release of plant root secretions,and the chemotaxis mediated by root secretions is an important prerequisite for plant growth promoting bacteria to colonize the rhizosphere of crops and play the role of growth promoting and biological control.In this study,from the perspective of systemic regulation,the above ground light environment affecting plant root exudates was studied.Serratia plymuthica A21-4 is a PGPR strain isolated from onion rhizosphere soil with strong colonization ability,remarkable growth promotion effect and resistance induction.However,it is not clear whether the interaction between light quality regulation and A21-4 can promote the changes of plant root exude components.And whether these changes directly affect the rhizosphere colonization ability of A21-4 and promote plant growth.This study focused on the light quality regulation of A21-4-tomato rhizosphere interactions.Firstly,the effects of different R/FR ratios on the colonization and growth promotion of A21-4 in the rhizosphere of tomato were studied.Then,the metabolomics method of LC-MS/MS technology was used to analyze the effects of different R/FR ratios on the components of tomato root extions inoculated and uninoculated with A21-4.The root exudates related to colonization were screened,and the roles of candidate root exudate components in A21-4 chemotaxis,biofilm formation and rhizosphere colonization were verified,and the mechanism of red light regulating A21-4 colonization in tomato rhizosphere through root exudates was finally revealed.Specific research results are as follows:Firstly,the regulation effect of high ratio red/far-red light(H-R/FR=2.5:1)on rhizosphere colonization of A21-4 in tomato was determined.It was found that A21-4 inoculation under high ratio of red light/far-red light significantly promoted the growth of wild-type tomato seedlings and the colonization density of A21-4 in tomato roots,while inoculation under low ratio of red light/far-red light(L-R/FR=1:2.5)showed no difference in plant height,fresh weight and the colonization density of A21-4 compared with the control.The results showed that H-R/FR and L-R/FR promoted and inhibited growth promotion and colonization of A21-4,respectively.Secondly,the primary metabolomics was analyzed to determine the effects of A21-4 inoculation on the components of tomato root exudates at different R/FR ratios.The results showed that the root exudates of tomato were significantly different among different treatments.After inoculation with A21-4,the metabolites of root exudates changed significantly under different R/FR light ratios.Thirdly,the influence of exogenous root exudate components on the chemotaxis of A21-4 and biofilm formation was determined.The results showed that L-Leucine,L-Methionine,L-Glutamine,D-Melezitose and 6-Aminocaproic acid all showed obvious chemotaxis to A21-4 and promoted the biofilm formation of A21-4.Fourthly,to verify the effects of exogenous root exudate components on growth promotion and rhizosphere colonization ability of A21-4 in tomato under different ratios of R/FR(H-R/FR=2.5:1,L-R/FR=1:2.5)light environment.The results showed that root exudates,including L-Leucine,L-Methionine,L-Glutamine,D-Melezitose and 6-Aminocaproic acid,all had alleviating effects on the growth and colonization ability of A21-4 inhibited by low proportion red light.Based on these results,we elucidated the mechanism of root secretion mediated red light regulation of plant A21-4 in rhizosphere colonization of tomato.The results of this study have important theoretical and practical significance for enriching the regulation mechanism of growth-promoting mycorrhizal colonization,accelerating the popularization and application of growth-promoting bacteria under field conditions,and using low-energy LED supplementing light and growth-promoting bacteria in facilities to regulate crop growth and stress resistance.