The Cloning And Expression Of Symbiotic Nitrogen Fixtion Genes In Medicago Sativa

Symbiotic nitrogen fixtion is the result of the interaction between rhizobia and legumes.In this process, rhizobia induce nodule development on plant roots.In order to investigate genes specific to nodule development and function in alfalfa, we used the cDNA-AFLP approach to get different expressed fragments.These expressed sequence tags(EST) offer the possibility of identifying new nodulin genes.To date, our analyses have revealed 65 ESTs. Of these ESTs,50% encode proteins with strong similarity to the known proteins ,29% encode novel proteins ,21% encode proteins with a low similarity to the GeneBank database.The ESTs with strong similarity were grouped into six categories,as fellows:(1)Seven fragments are likely involved in signal transduction,in -eluding aprotein phosphatase 2c(pp2c)(Rx31),a ATPase(calcium-tra- ntransporting)(Rx36),a G protein-coupled recepter(Rx44),a acalcium-binding protein(Rx81),a Ras-related protein RabllC(Rx84),a putative receptor-like protein kinase(Rx96) and a cytosolic phosphoglycerate kinase(Rx100).(2)Two fragments are likely involved in plant defense response, including a RelA/spoT-like protein RSHI(Rx49) and a resistance protein MG13(Rx79).(3)Six fragments are likely involved in transcription and regulation ,including aputative RING-H2 zinc finger protein(Rx12),a snf2-related CBP activator protein (Rx67),a DNA-binding protein-like (Rx86),a reverse transcriptase (Rx88),a 70KDa heat shock protein (Rx89) and putative transposable element(Rx29)(4)One fragment is likely involved in secondary metabolism, inc- luding the epoxide hydrolases (Rx32).(5)Four fragments are likely involved in nutrient transport and metabolism,including a putative membrane trafficking factor (Rx33),a amino acid transporter(Rx21),a sugar transporter(Rx46) and dipeptidyl peptides IV-like protein(Rx60)(6)Three fragments are likely involved in other basic genes,inc- luding a DNA polymerase alphal(Rx22),a putative poly(A) polymerase (Rx26) and a ribosomal protein (Rx48).We have cloned a full-length cDNA sequence of NB-ARC resistance gene by assembling short ESTs .We have tried on screening the cDNA library of 15 days Medicago saliva nodule induced by Rm1021 with the EST(Rx2) as the probe.