大豆响应低磷胁迫的XTH基因鉴定及XTH38调节根系生长研究

  【目的】  鉴定大豆木葡聚糖内糖基转移酶/水解酶 (xyloglucan endotransglycosylases/hydrolases, XTHs) 基因家族，分析其表达模式和对低磷养分胁迫的响应，初步明确大豆XTH38调节根系生长的功能。  【方法】  供试大豆品种为粤春03-3 (YC03-3)，拟南芥野生型为哥伦比亚 (Columbia-0，Col-0) 生态型。通过生物信息学方法，鉴定了大豆XTH基因家族成员，并对大豆的XTH家族成员进行进化分析。采用水培方法，设定高磷对照(HP，KH₂PO₄ 500 μmol/L)和低磷处理(LP，KH₂PO₄ 25 μmol/L)营养液培养，将大豆幼苗处理14天后，取大豆幼苗的根和叶，使用定量PCR分析幼苗中5个GmXTHs的表达；将在1/2 MS固体培养基上发芽2天的超表达GmXTH38株系和Col-0分别接种到HP、LP、低铁 (LFe，Fe 0 μmol/L)、中铁(MFe，Fe 50 μmol/L)和高铁 (HFe，Fe 500 μmol/L)固体培养基上，7天后测定GmXTH38株系的侧根长度和密度。  【结果】  通过生物信息学分析，确定了大豆XTH基因家族共有61个成员，分为3个不同亚组，其中GmXTH38与AtXTH9、AtXTH23位于同一亚组。定量PCR分析结果表明，GmXTH基因家族成员在大豆器官或组织的表达模式不同，其中GmXTH28、GmXTH38、GmXTH41和GmXTH52受LP诱导表达，特别是GmXTH38在大豆根和叶中的表达均受LP诱导。与大豆一致，LP条件下GmXTH38启动子在拟南芥幼苗根、叶的活动强于HP处理。在高磷和中铁(植物正常生长养分需求量)条件下，拟南芥异源超表达GmXTH38抑制拟南芥主根生长、侧根数目和侧根密度。在LP、LFe和HFe胁迫下，与Col-0相比，超表达GmXTH38拟南芥材料主根变短、侧根数和侧根密度减少；超表达GmXTH38导致Col-0侧根形成对LP的敏感性增加；超表达GmXTH38导致Col-0侧根密度在LFe或HFe胁迫条件下下降程度更明显，超表达GmXTH38增加拟南芥主根生长对LFe或HFe的敏感性。  【结论】  大豆基因组存在61个XTH成员，分别为GmXTH1~GmXTH61。GmXTH38在大豆根叶均受LP诱导。超表达GmXTH38 在正常养分条件下抑制拟南芥主根生长和侧根数目；超表达GmXTH38改变拟南芥根系在磷铁养分胁迫条件下的生长。

Identification and assessment of the role of soybean low phosphate-responsive Xyloglucan endotransglycosylases/hydrolases genes in root growth

  【Objectives】  To identify soybean xyloglucan endotransglycosylases/hydrolases (XTHs) gene family, analyze their expression pattern and responses to low phosphorus (P) stress, and preliminarily explore the role of soybean XTH38 in root growth.   【Methods】  The tested crops were soybean cultivar Yuechun 03-3 (YC03-3), and the wild type of Arabidopsis thaliana called Columbia (Columbia-0, Col-0) ecotype. A total of 61 XTH genes were identified in soybean by bioinformatics methods, and evolutionary analysis of soybean XTH family members was performed. Using the hydroponics method, two nutrient solutions of high P (HP, control) and low P (LP) were set, and soybean seedlings were treated for 14 days. The roots and leaves of soybean seedlings were sampled, and the expression level of 5 GmXTHs in the seedlings was analyzed by quantitative real time PCR. The transgenic method revealed the function of GmXTH38 in regulating the main root growth and lateral root formation of Arabidopsis thaliana under nutrient stress conditions such as LP, low iron (LFe) and high iron (HFe).   【Results】  Bioinformatics analysis revealed that soybean XTH family had 61 members and 3 different subgroups, among which GmXTH38 was in the same subgroup as AtXTH9 and AtXTH23. Quantitative real time PCR was used to explore responses of GmXTH to low P stress. We found that GmXTH family members had different expression patterns in soybean organs or tissues, among which GmXTH28, GmXTH38, GmXTH41 and GmXTH52 were induced by LP. GmXTH38 in soybean roots and leaves were induced by LP. In contrast to HP, the activities of GmXTH38 promoter in Arabidopsis seedling roots and leaves was enhanced in LP. Ectopic overexpression of GmXTH38 revealed that under full nutrient conditions, namely high P or middle iron, overexpression of GmXTH38 inhibited primary root growth, number of lateral roots, and decreased density of lateral root. Under LP, LFe or HFe stress, compared with the wild Col-0, the overexpression of GmXTH38 in Arabidopsis resulted in shortened primary root, decrease in lateral roots and density of lateral roots. In contrast to Col-0, overexpression of GmXTH38 resulted in higher sensitivity of lateral root formation to low P. Overexpression of GmXTH38 resulted in a more pronounced decrease in Arabidopsis density of lateral root under LFe or HFe stress. Overexpression of GmXTH38 increased the sensitivity of Arabidopsis primary root growth to LFe or HFe.   【Conclusions】  A total of 61 XTH genes (GmXTH1–GmXTH61) were identified in soybean genome. GmXTH38 was significantly induced by low P in roots and leaves. Overexpression of GmXTH38 in Arabidopsis inhibits primary root growth and lateral root formation in full nutrient conditions. Overexpression of GmXTH38 in Arabidopsis alters root growth in response to phosphorus or iron stress.