Isolation and functional analysis of MxCS3: a gene encoding a citrate synthase in Malus xiaojinensis, with functions in tolerance to iron stress and abnormal flower in transgenic Arabidopsis thaliana

Abstract

Iron (Fe) is one of the essential micronutrients required by all plants. Citric acid is considered as the chelate substance in the long distance transport of Fe. In this study, a gene encoding putative citrate synthase was isolated from Malus xiaojinensis and designated as MxCS3. The MxCS3 gene encoded a protein of 235 amino acid residues with a theoretical isoelectric point of 9.47 and a predicted molecular mass of 26.3 kDa. Subcellular localization study revealed that MxCS3 is preferentially localized in mitochondrion and cytoplasmic membrane. The expression of MxCS3 was enriched in leaf, phloem, and root, which was highly affected by Fe stress, indoleacetic acid and abscisic acid treatment in M. xiaojinensis seedlings. When MxCS3 was transferred into Arabidopsis thaliana, it improved Fe stress tolerance in transgenic Arabidopsis. Increased expression of MxCS3 in transgenic A. thaliana also led to increased fresh weight, root length, CS activity, and the contents of chlorophyll, citrate acid, Fe and Zn, especially when dealt with Fe stress. More importantly, we firstly found that ectopic expression of MxCS3 resulted in abnormal flowers in transgenic Arabidopsis.