Sugar Transporter Genes In Tomato And Rice Regulated By Mycorrhiza

Originated about 400 million years ago,arbuscular mycorrhizas(AM) are mutualistic symbiosis formed between beneficial soil fungi of the phylum Glomeromycota and over 80%of land plant species.This symbiotic relationship has enormous impacts on terrestrial ecosystem.In AM symbiosis,the nutrient exchange is mainly finished by phosphate transporter,sugar transporter and plasma membrane H~+-ATPase.Researches on nutrition exchange between AM fungi and the host plant is essential to uncover the beneficial symbiotic mechanisms.However,there have been few studies devoted specifically to sugar transport in AM symbiosis.So investigations on sugar transporter genes will conduce to interpret the transport and allocation mechanisms of carbohydrates synthesized by the host plant,and intergrally elucidate the whole molecular transport mechanism in the AM symbiosis.In this study,(1) using the model plant of dicotyledon,the altered phosphate concentration and soluble sugar content in tomato after the form of AM symbiosis were detected.The different expression patterns of sugar transporter genes under the infection and the localization of LEST3 were investigated.(2) using the model plant of monocotyledon,the regulation of mix AM fungi on sugar transporter genes in rice were studied.The main results are shown as follows:1.We investigated the effects of AM symbiosis on Pi concentration and soluble sugar content in tomato under the infection with G.intraradices or G.caledonium.The results indicated that inoculation with G.caledonium or G.intraradices increased the concentration of total Pi by 25-40%in the tomato leaves and roots at the low Pi supply level of 0.05 mM;total soluble sugar content in per plant increased,but a moderate decrease in soluble sugar concentration in inoculated plants was observed.2.Using reverse transcriptase PCR(RT-PCR),we analyzed the effects of mycorrhiza and phosphate on the expression of seven putative sugar transporter genes in tomato plants.The expression of LeSUT1 and LeHT2,classified,respectively,as putative sucrose and hexose transporter genes,were down-regulated in the roots inoculated with AM fungi G.caledonium or G.intraradices.Unexpectedly,the expression of LeST3,a putative monosaccharide transporter gene,was decreased by inoculation of Glomus caledonium,but was enhanced by inoculation of Glomus intraradices in both the roots and leaves.High-Pi in tomato decreased the expression of LeHT2 and LeST3 in roots,and enhanced that of LeHT2 in the leaves.The expression of LeSUT2,LeSUT4,LeHT1 and LeHT3 were neither regulated by AM,nor by phosphate.3.RNA in situ hybridization showed that LeST3,remarkably regulated by AM,were located in root cortical cells harboring mycorrhizal structures.This result better confirms that LeST3 is probably involved in the nutrient exchange via the arbuscule-cortical cell (periarbuscular) interface.4.Infected with mix AM fungi,we investigated the regulation of four sugar transporter genes in rice.The result indicated that the AM symbiosis had no obvious impact on the expression of OsSUT2,OsSUT4,but enhanced the expression of OsMST4 and OsMST7 in roots.