Responses of FER family genes in Glycine max to low phosphorus stress and iron toxicity and the role of GmFER1 in iron toxicity tolerance

Objectives FERRITIN (FER) is a kind of conserved ferritin. FER plays important roles in maintaining iron ion homeostasis and iron metabolism. We identified Glycine max FERRITIN (FER) genes, determined the responses of GmFERs to low P stress and Fe toxicity, and deciphered the roles of GmFER1 in iron tolerance via heterologous expression.

Methods The GmFER genes were identified via bioinformatics technique. Based on the encoded amino acid sequence of GmFERs, the relative molecular weight, amino acid composition and isoelectric point (PI) of GmFER family were calculated by ProtParam program. The subcellular localization of GmFERs was predicted by PSORT. The MEME suite was used to explore the conserved motifs in GmFER family. The phylogenetic tree was reconstructed by maximum likelihood method via MEGA X. Quantitative real time PCR was used to analyze the responses of GmFERs to low phosphorus (P) and iron toxicity. We constructed the vector of GmFER1 gene promoter fused with GUS reporter gene and overexpressing GmFER1 vector, and further analyzed the promoter activity of GmFER1 gene and its response to iron toxicity in Arabidopsis, as well as the effect on Arabidopsis thaliana tolerance to iron toxicity.

Results Soybean genome encodes 12 FERs. GmFERs can be divided into four subgroups (subgroups Ⅰ–Ⅳ), among which GmFER3, GmFER7, GmFER8, GmFER10 and GmFER11 belong to subgroup Ⅰ, GmFER2 and GmFER9 belong to subgroup Ⅱ; together with FERs from gramineous rice and maize, GmFER5 belongs to subgroup Ⅲ, and GmFER1, GmFER4, GmFER6, and GmFER12 belong to subgroup Ⅳ. The MEME suite predicted that there were three conserved motifs in the GmFER family. Subcellular localization prediction revealed that GmFERs appear to be localized in cytoplasm, mitochondria and chloroplast. Quantitative real time PCR analysis showed that 12 GmFER genes were differentially responsive to P and iron nutrient stress. Among them, GmFER1, GmFER4, GmFER5, GmFER6 and GmFER12 were induced by low P, and the expression of GmFER1, GmFER4, and GmFER12 was induced by iron toxicity. Iron toxicity promoted the activity of GmFER1 promoter in roots. Under iron toxicity stress, compared with wild-type Col-0, overexpressing GmFER1 significantly increased the length of primary root, number of lateral roots, lateral root density, chlorophyll content, and fresh weight of Arabidopsis, thus enhancing iron toxicity resistance.

Conclusions Soybean genome encodes 12 GmFERs. GmFER genes respond to low P or iron toxicity. Overexpression of GmFER1 improves the growth of transgenic Arabidopsis under iron toxicity via promoting primary root growth, lateral root formation, increasing lateral root density, chlorophyll content and fresh weight. Our results indicate that GmFER1 plays important roles in alleviating iron toxicity stress and enhancing the ability of plants to tolerate iron toxicity.