Mechanisms Of Transcription Factor HY5 Induced The Synthesis Of Strigolactones And Fatty Acids To Regulate Arbuscular Mycorrhiza Symbiosis In Tomato

Phosphorus is an indispensable element for plants growth and development.However,it always be insoluble compounds or organic compounds in soil and cannot be absorbed and utilized by plants.Luckly,using beneficial microorganisms,such as arbuscular mycorrhiza fungi（AMF）could solve this problem in agricultural production.Together with plant roots,AMF could form a symbiotic system,improving plants’photosynthetic rate,morphology and resistance to stresses,besides providing host plants with water and mineral elements such as phosphorus,nitrogen,potassium and iron.Moreover,arbuscular mycorrhiza symbiotsis could benefit a lot such as reducing abuse of fertilizers,promoting cycle of carbon,phosphorus and nitrogen,balancing rhizosphere microbial community,improving soil structure and properties,and realizing sustainable development of agricultural ecological environment.Tomato（Solanum lycopersicum）is one of the most important vegetable crops in China,possessing great potential in developing modern facility agriculture.Meanwhile,tomato as a model plant for botany research.This article explored the impacts and mechanisms of environmental factors regulation on AM in tomato by using genetics,molecular biology,plant physiology,biochemistry and so on.The main research results are as follows:1.Exploring the mechanisms of environmental factors on SLs and AM in roots of tomato.According to experiments that setted different environmental factor variables,we confirmed that low phosphate,e CO₂ and H-R/FR could increase the transcripts of the SLs synthesis genes CCD7,CCD8 and MAX1 in roots of tomato.Using VIGS technology to obtain CCD7,CCD8 and MAX1 silencing plants,we ascertained that SLs synthesis genes were involved in e CO₂ promoting formation of AM.Using the CRISPR/Cas9 mutant strain of CCD7,we confirmed the SLs synthesis gene mediated the regulation of tomato AM by red-light,and thus contributing to phosphorus absorption through the AM pathway.2.Exploring the regulation of light signals on AM in tomato.Using tomato phytochrome mutants to detecte the related indicators of SLs in the roots of tomato and AM symbiosis.It proved the positive regulation of phy B on the synthesis of SLs,formation of AM and uptake of phosphate in tomato.Experiment using phytochrome mutants and grafting techniques showed that shoots phy B dominating the above regulation mechanism.3.Searching for the systemic signal that mediating the shoots phy B regulation on AM.Using protein immunoprecipitation and grafting techniques,we found that shoots phy B could increase HY5 protein in roots of tomato.In order to explore whether HY5was involved in the regulation of AM by the shoots phy B,we used the CRISPR/Cas9mutant strain of HY5.The results showed that HY5 could positively regulate SLs synthesis,AM formation and phosphorus absorption in tomato.The grafting experiment clarified that shoots HY5 dominated this regulation process.4.Exploring the molecular mechanism of HY5 in regulating AM in tomato.Using protein immunoprecipitation and grafting techniques,we found that tomato HY5protein could move from the shoots to roots,which proving that HY5 protein was the systematic signal involved in the regulation of AM by the shoots phy B.Using EMSA,Ch IP and dual luciferase reporter gene system,we confirmed that HY5 protein could bind to G-box in promoters of three SLs synthetic genes in vitro and in vivo,with promoting their transcripts.These results proved the transcription factor role of HY5 in regulation of tomato AM.5.Analysing how HY5 regulates the synthesis of fatty acids in AM roots of tomato.According to the BLAST results and gene expression,we found a gene Sl Fat Mc,coding AM-specific C16:0-ACP thioesterase,which positively effected in tomato AM.It was similar that the dynamic changes of Sl Fat Mc transcripts and HY5 protein in the AM roots of tomato.Using HY5 related plants,we found that HY5 could promote expression of Sl Fat Mc in AM roots,and increase the contents of C16:0,C16:1ω5 fatty acids and the ratio of hexadecyl fatty acids in AM roots.EMSA and dual luciferase reporter gene system proved that HY5 could bind to the ACE element on the promoter of Sl Fat Mc and thus promoting its transcripts.Based on the above results,we determined that the environmental factors such as low phosphate,e CO₂ and red light could regulate formation of AM and phosphate absorption by promoting synthesis of SLs in tomato.In-depth exploring the regulation mechanism of light on tomato AM,the results showed that HY5 played important roles in transmitting systemic signaling of red light-phy B and regulating the expression of SLs synthesis genes.Meanwhile,HY5 could regulate biosynthesis of hexadecyl fatty acids in AM colonized cells to further promote AM development and nutrition exchange between host plant and AMF.These conclusions clarify molecular mechanisms of AM formation in roots of plants and provide a scientific basis for improving effectiveness of AM in facility agriculture.