Root Biology Centre, South China Agricultural University, Guangzhou 510642, China.
Plant J. 2011 May;66(3):541-52. doi: 10.1111/j.1365-313X.2011.04511.x. Epub 2011 Mar 7.
Root system architecture responds plastically to some abiotic stresses, including phosphorus (P), iron (Fe) and water deficiency, but its response mechanism is still unclear. We cloned and characterized a vegetative β-expansin gene, GmEXPB2, from a Pi starvation-induced soybean cDNA library. Transient expression of 35S::GmEXPB2-GFP in onion epidermal cells verified that GmEXPB2 is a secretory protein located on the cell wall. GmEXPB2 was found to be primarily expressed in roots, and was highly induced by Pi starvation, and the induction pattern was confirmed by GUS staining in transgenic soybean hairy roots. Results from intact soybean composite plants either over-expressing GmEXPB2 or containing knockdown constructs, showed that GmEXPB2 is involved in hairy root elongation, and subsequently affects plant growth and P uptake, especially at low P levels. The results from a heterogeneous transformation system indicated that over-expressing GmEXPB2 in Arabidopsis increased root cell division and elongation, and enhanced plant growth and P uptake at both low and high P levels. Furthermore, we found that, in addition to Pi starvation, GmEXPB2 was also induced by Fe and mild water deficiencies. Taken together, our results suggest that GmEXPB2 is a critical root β-expansin gene that is intrinsically involved in root system architecture responses to some abiotic stresses, including P, Fe and water deficiency. In the case of Pi starvation responses, GmEXPB2 may enhance both P efficiency and P responsiveness by regulating adaptive changes of the root system architecture. This finding has great agricultural potential for improving crop P uptake on both low-P and P-fertilized soils.
根系结构对一些非生物胁迫具有可塑性响应，包括磷（P）、铁（Fe）和水分亏缺，但响应机制尚不清楚。我们从磷饥饿诱导的大豆 cDNA 文库中克隆和鉴定了一个营养生长β-扩张蛋白基因 GmEXPB2。35S::GmEXPB2-GFP 在洋葱表皮细胞中的瞬时表达证实 GmEXPB2 是一种定位于细胞壁的分泌蛋白。GmEXPB2 主要在根中表达，且对磷饥饿高度诱导，这一诱导模式在转基因大豆毛状根的 GUS 染色中得到了证实。过表达 GmEXPB2 的完整大豆复合植株或含有敲低构建体的毛状根的研究结果表明，GmEXPB2 参与毛状根伸长，随后影响植物生长和 P 吸收，特别是在低 P 水平下。非整倍体转化系统的结果表明，在拟南芥中过表达 GmEXPB2 增加了根细胞分裂和伸长，并增强了植物生长和 P 吸收，在低 P 和高 P 水平下均如此。此外，我们发现除了磷饥饿之外，GmEXPB2 还被铁和轻度水分亏缺诱导。总之，我们的结果表明，GmEXPB2 是一个关键的根β-扩张蛋白基因，它内在地参与了根系结构对一些非生物胁迫的响应，包括 P、Fe 和水分亏缺。在磷饥饿响应中，GmEXPB2 可能通过调节根系结构的适应性变化来增强 P 效率和 P 响应性。这一发现为提高作物在低 P 和 P 施肥土壤中的 P 吸收具有重要的农业潜力。
