Abstract：In order to study the iron absorption and utilization molecular mechanism of different Fe efficiency genotypes apple rootstocks, we used the Malus baccata Borkh as material, which is an iron-inefficient genotype apple rootstock. Through the full-length of citrate synthase gene MxCS1 was obtained from M. xiaojinensis, which is an iron-efficient genotype apple rootstock and previous studies have shown that it is related to iron absorption and transport, and their specific primers were designed to clone the citrate synthase gene(CS) from cDNA of M. baccata Borkh by using RT-PCR, which was composed of 1 422 bp and had high homology with the gene encoding citrate synthase in Golden Delicious(M. domestica Borkh ) and M. xiaojinensis, thus we designated it as MbCS1(GenBank accession No. JQ898346). The bioinformatics analysis showed that citrate synthase gene from M. baccata Borkh encoded 473 amino acids, whose relative molecular weight was 54.26 kD and theoretical isoelectric point was 8.95. Subcellular localization assay of the MbCS1 protein, which used transient expression of MbCS1::GFP fusion protein in onion(Allium cepa) cells by particle bombardment, displayed that MbCS1 encoding protein localized in cell membrane. RT-PCR and Real-time PCR analysis suggested that MbCS1 gene was expressed in roots, shoots and leaves in M. Baccata Borkh under normal supply of iron; and the expression of MbCS1 gene was enhanced obviously in roots, shoots and leaves under a low iron concentration(EDTA-NaFe, 4 μmol/L) and reached to the highest value at the ninth day, then decreased; the expression of MbCS1 gene was different in roots, shoots and leaves, enriched in shoots than that in leaves and roots under ion deficiency induced. The expression pattern of MbCS1 gene in M. baccata Borkh was very different from MxCS1 gene in M. xiaojinensis. The result provides solid foundation for further study of the resistance mechanisms in higher plants and provides basis for improvement of iron-inefficient apple rootstocks
