Study On Aluminum Resistance Genes In Medicago Sativa L.

Severe crop yield losses are caused by the rhizotoxicities of aluminum (Al³⁺) andprotons （H⁺） in acid soil. Some plant species and cultivars have evolved mechanisms fordetoxifying Al³⁺and H⁺, but little is known about molecular mechanisms of theirtolerance. Here, we cloned two genes MsSTAR1and MsSTAR2in alfalfa, homologs ofOsSTAR1and OsSTAR2in rice which function in aluminum tolerance.MsSTAR1（GenBank accession No. KC430620） encodes a nucleotide bindingdomain of a bacterial-type ABC transporter in Medicago Sativa L., and shares a highsimilarity with rice OsSTAR1and Arabidopsis AtSTAR1, which have been implicated inaluminum tolerance.780bp-coding sequence of MsSTAR1encodes a259-amino acidprotein. MsSTAR1was constitutively expressed in all tissues and it was predominantlyexpressed at basal roots（1-2cm） and leaves. Different with OsSTAR1and AtSTAR1,either Al³⁺or H⁺increased the expression of MsSTAR1. The expression of MsSTAR1increased with aluminum concentration in ‘Zhongmu No.1’ alfalfa, but the gene didn’trespond to other metal ions. Furthermore, we found that there is no positive correlationbetween the amount of gene expression and aluminum resistance in Medicago Sativa L.The level of gene expression reaching the maximum at12h after the exposure to Alindicates that the gene was not immediately induced but has a delayed expression. Allthese results indicate that MsSTAR1is an aluminum-activated gene in Medicago SativaL., and it may induce the protection mechanism caused by aluminum damage, whichprobably function as a bacterial-type ABC transporter by forming a complex with atransmembrane protein.We report a gene, MsSTAR2（GenBank accession No. KC430619）, encoding atransmembrane domain of a bacterial-type ABC transporter in Medicago Sativa L., andshares a high similarity with rice OsSTAR2and Arabidopsis AtALS3, which have beenimplicated in aluminum tolerance.864bp-coding sequence of MsSTAR2encodes a287-amino acid protein. MsSTAR2was constitutively expressed in all tissues and it waspredominantly expressed at leaves. Different with OsSTAR2and AtALS3, either Al³⁺orH⁺increased the expression of MsSTAR2. The expression of MsSTAR2increased withaluminum concentration in ‘Zhongmu No.1’ alfalfa, but the gene didn’t respond to othermetal ions, such as Cd²⁺, Mn²⁺. Furthermore, we found that there was no positivecorrelation between the amount of gene expression and aluminum resistance in Medicago Sativa L. The level of gene expression reaching the maximum at12h after theexposure to Al indicates that the gene was not immediately induced but has a delayedexpression. All these results indicate that MsSTAR2is an aluminum-activated gene inMedicago Sativa L., and it may induce the protection mechanism caused by aluminumdamage, which probably function as a bacterial-type ABC transporter by forming acomplex with a nucleotide binding domain protein.