大豆磷铁养分胁迫响应的FER基因鉴定及FER1缓解铁毒作用

  【目的】  FERRITIN (FER)是一类保守铁蛋白，对于维持铁的稳态及铁代谢中起重要作用。通过鉴定大豆FERRITIN (GmFER)基因家族的组成及其对低磷、铁毒等养分胁迫的响应，为今后研究FER功能奠定基础。  【方法】  对GmFER基因进行生物信息学分析，根据其编码的GmFER氨基酸序列，用ProtParam tool网站计算了GmFER家族的相对分子质量、氨基酸组成和等电点(PI)；用PSORT网站预测GmFERs蛋白定位；从Phytozome网站下载GmFER家族的氨基酸序列与基因启动子序列，用 MEME 预测GmFER家族序列中的保守基序；用MEGA X对GmFERs进行进化分析，用最大似然法重建进化树；通过定量PCR分析GmFER对低磷、铁毒等养分胁迫的响应，构建GmFER1基因启动子融合GUS 报告基因的载体与GmFER1超表达载体，进一步分析GmFER1基因启动子活性和对铁毒的响应，以及异源超表达GmFER1对拟南芥耐受铁毒的影响。  【结果】  大豆基因组有12个GmFER基因，对GmFERs进行进化分析，发现GmFERs可以分为4个亚组(亚组Ⅰ～Ⅳ)，其中GmFER3、GmFER7、GmFER8、GmFER10和GmFER11属于亚组Ⅰ，GmFER2和GmFER9同属亚组Ⅱ；GmFER5和禾本科植物水稻和玉米的FER同属亚组Ⅲ，GmFER1、GmFER4、GmFER6、GmFER12属于亚组Ⅳ；通过MEME预测，GmFER家族序列中的保守基序有3个；蛋白亚细胞定位预测显示，大豆FER蛋白可定位于细胞质、线粒体和叶绿体。运用定量PCR技术检测GmFER基因在大豆根和叶的表达水平，发现12个GmFER基因在响应磷铁养分胁迫时存在差异，其中GmFER1、GmFER4、GmFER5、GmFER6、GmFER12受低磷诱导，GmFER1、GmFER4、GmFER12表达受铁毒诱导；对GmFER1启动子的活性进行分析，发现铁毒促进GmFER1启动子在根系的活性；在铁毒胁迫下，与野生型Col-0比，超表达GmFER1显著提高了拟南芥的主根长、侧根数目、侧根密度、叶绿素含量和鲜重，增强了耐铁毒的能力。  【结论】  大豆基因组共有12个FER基因，GmFER基因响应低磷或铁毒等养分胁迫。超表达GmFER1可促进主根生长，增加侧根密度，提高叶绿素含量，增加植株鲜重，表明GmFER1在缓解铁毒胁迫方面起重要作用。

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.