Research On Molecular And Physiological Mechanism Of The Phosphate Accumulation Variation In Different Astragalus Sinicus Varieties

Astragalus sinicus?A.sinicus?is a commonly used legume green manure,which can fix atmospheric N₂ and accumulate inorganic phosphorus efficiently.It releases large amounts of mineral nutrients and organic substances to the soil after decomposing,which is beneficial to soil and the following crops.However,the genotypic variation and molecular mechanism for Pi-uptake and Pi-storage in A.sinicus are still obscue.Here,this study analyzed the morphological responses of six A.sinicus varieties?XB,YJ,YZ,XZ,WZ,XF?from different regions of China,to the external Pi availabilities and determined their Pi accumulation.The research also identified the full-length transcripts of some Pi-signaling and Pi-homeostasis genes using the third-generation sequencing technique.In addition,the research determined the expression levels of these genes using qRT-PCR from low Pi sensitive and tolerant varieties.Finally,this study revealed phosphate accumulation variation in Astragalus sinicus varieties.The main results are as following:?1?Different A.sinicus varieties responded to external Pi availibilites distinctly:The growth of YJ were dramatically inhibited by Low Pi stress,but XZ was not.Among 6 A.sinicus varieties,XZ has the highest Pi content,and YJ has the lowest Pi content.The anthocyanin contents of YJ were dramatically increased by Low Pi stress,but the anthocyanin contents of XZ were not dramatically affected.These results suggested that XZ was more tolerant to low-P stress compared to YJ.?2?AsIPS1/2?two Pi-starvation induced marker genes?,AsPHR1/2?two central regulators of Pi signaling?,AsSPX1-5?five SPX domain containing proteins?,AsPT1-8?eight plasma membrane Pi transporters?,AsSPX-MFS1/2?two vacuolar Pi influx transporters?,and AsVPE1?a vacuolar Pi efflux transporter?were identified from the cDNA database of A.sinicus.We showed that AsVPE1 was located on vacuolar membrane,and conferred Pi transport activity cross membrane in yeast.The analysis indicated that Pi-starvation signaling system was conserved between A.sinicus and other model species,such as Arabidopsis and rice?3?The expression of Pi-starvation signaling genes?As IPS1/2,AsSPX2/4/5?and plasma membrane Pi transporter genes?AsPT2/5/6/7?were strongly induced by Pi deficiency;and the expression of neither Pi-starvation signaling genes nor the plasma membrane Pi transporter genes were significantly different between YJ and XZ.?4?Under Pi deficient stress,the expression of vacuolar phosphate influx transporters?AsSPX-MFS1/2?was down-regulated,however,that of vacuolar phosphate efflux transporter?AsVPE1?was induced.Further analysis showed that the expression of AsSPX-MFS1/2 in YJ was significantly lower than those in XZ,while the expression of AsVPE1 was significantly higher than that in XZ under MP and LP treatments.It suggested that the expression of vacuolar Pi influx transporter genes AsSPX-MFS1/2 was positively correlated with the Pi accumulation between A.sinicus varieties;whereas the expression of vacuolar Pi efflux transporter gene AsVPE1 was negatively correlated between them.In summary,different A.sinicus varieties responded to external Pi availiabilites distinctly and accumulated different levels of Pi.However,the key regulators in Pi homeostasis pathway are conserved between A.sinicus and other model species,such as Arabidopsis and rice.Distinct Pi accumulation pattern between different varieties could be explained by the variable abundance of vacuolar Pi transports.Moreover,determination of vacuolar Pi transporters expression could be used to select A.sinicus varieties with high-Pi accumulation.