The Mechanism Of Arbuscular Mycorrhizal Promoted Tomato To Absorb Phosphorus Under The Red Light And CO₂ Enrichment Condition

Light is not only the energy source of plant photosynthesis,but also is the important signal to participate in the regulation of plant growth and stress responses.CO₂ is also the main raw material for photosynthesis of plant and the concetration of CO ₂directly affecting the photosynthetic rate of plant,plant growth,resistances and so on.Phosphorus is an necessary element for plant growth and development,affecting the yield and quality of crops,agricultural production in recent years leading to the lack of phosphorus in the soil.The effectiveness of the phosphorus concentration in the soil limit the growth of plant.The symbiosis between mycorrhizal fungi and plants can promote the absorption of water and mineral elements in soil,especially phosphorus.Currently,the effectivenesses of CO₂ enrichment and red light on plant growth and resistance have often been reported,but their influences of CO₂ enrichment and red light on mycorrhizal fungi and phosphorus remain unexplored.Meanwhile,the concrete molecular mechanism also need to explore.In this study,tomato（Solanum lycopersicum L.）was used as material to investigate the influence of red light on AMF parasitism and phosphorus uptaking by tomato and elevated CO₂induced phosphorus uptaking is mediated by IAA and H₂O₂,from IAA signal,H₂O₂signal,phosphorus concentration,dry weight and mycorrhizal infection rate through grafting,the RNA interference technology,GUS staining and blue staining technology.The results are as follows:1.We have studied the red light affected AM mycorrhizal and the absorption of phosphorus in tomato in low phosphorus condition.Through experiments,we found that the phosphorus concentration,phosphorus content and dry weight of WT,phy A,cry1 plants were significantly increased,but did not affect phy B1B2 plants after moculated with mycorrhizal fungi in low phosphorus enviroment.Meanwhile,we also found that WT,phy A,cry1 plants promoted the growth of tomato root mycorrhizal fungi.The infection rate and infection density of mycorrhizal fungi in WT,phy A,cry1plants were significantly highter that in phy B1B2 plants.The results indicated that in low phosphorus environment the growth of mycorrhizal fungi was promoted by photosensitive pigment phy B,which alleviated the phosphorus stress.2.We have studied the role of IAA in light-systemic regulated phosphorus absorption of tomato.In low phosphorus environment,WT,phy A,cry1 induced transcript of flavinmonooxygenase（FZY）（a step—limiting gene in IAA biosynthesis）and strigolactone biosynthetic genes MAX1,CCD7,CCD8 and signaling genes MAX2,but these physiological indexes of phy B1B2 haved not changed.The results showed that the photosignal was used to prom ote the synthesis of IAA and SLs in tomatoes by photosensitive pigment phy B 1B2 to regulate phosphorus absorption.DR5::GUS grafting tomato seedlings:WT/DR5::GUS,phy A/DR5::GUS,phy B1B2/DR5::GUS,cry1/DR5::GUS were treatmented in low phosphorus condition.The results showed that compared with the grafting plant WT/DR5::GUS,the relative expression of FZY,PIN1（a marker gene for PAT）,IAA15（a marker gene of IAA signalling）,PT1 and PT2（marker genes for phosphorus absorption）and the IAA content were increased,but the above indicators in phy B1B2/DR5::GUS grafting plants were decreased.At the same time,the root tip of DR5::GUS intensity of WT/DR5::GUS,phy A/DR5::GUS and cry1/DR5::GUS grafting plants were highter than phy B1B2/DR5::GUS grafting plants.In low phosphorus environment,DR5::GUS of tomato genetically modified material plants were treated respectively in the dark,red,far red and blue light with 12 hours,the results showed that the red and blue light treatment induced DR5::GUS intensity increasing,far red light did not alter the intensity in the root.At the same time,the plants of PIN1,IAA15,PT1,PT2 gene expression level were increased by the red and blue light treatments,but did not change in the plants by far red light treatment.The resu lts showed that red light was mediated by the synthesis and transport of IAA to promote phosphorus absorption.3.We have studied H₂O₂ and IAA regulated the absorption of phosphosphorus in tomato under CO₂ enrichment and low phosphorus environment.The results showed that the content of H₂O₂ in tomato plants was increased,and RBOH1 gene expression of H₂O₂ increased under the treatment of CO₂ enrichment and low phosphorus conditions.At the same time,H₂O₂ subcellular localization results showed that H ₂O₂was mainly accumulated in the cell wall of mesophyll cells that face intercellulars paces,these results showed that CO₂enrichment promoted the accumulation of H₂O₂ in the apoplastic of leaves.Using RBOH1-RNAi mutant materials,the results showed that IAA content of WT plants was enhanced by CO₂ enrichment and low phosphorus treatment,but IAA content of RBOH1-RNAi plant was not changed.Using WT/DR5::GUS,rboh1/DR5::GUS,dgt/DR5::GUS grafting plants as the experimental materials,the results show that in CO₂ enrichment and low phosphorus environment,the DR5::GUS intensity of WT/DR5::GUS plant was increased,while the DR5::GUS intensity of rboh1/DR5::GUS and dgt/DR5::GUS were not changed.At the same time,in CO₂enrichment and low phosphorus environment,WT/DR5::GUS plant root phosphorus uptaking genes of PT1 and PT2 were induced,but not in the same in rboh1/DR5::GUS and dgt/DR5::GUS plants.The above results showed that H₂O₂ and IAA mediated the absorption of phosphorus in tomato plants under CO ₂enrichment,while H₂O₂ may play a role upstream of IAA.