水稻抗铝毒新基因SAL3的克隆和功能解析

Aluminum (Al) toxicity is a major constraint of crop production on acid soils, which represent more than 30% of arable lands in the world. Currently, Al-induced inhibition of root growth is mainly attributed to the disruption of cell elongation. Nevertheless, it is unclear whether Al-induced root growth inhibition can be mediated through the inhibition of cell division. Rice is a highly Al-resistant crop, but the molecular mechanisms underlying the high Al resistance are still not fully understood. We obtained a rice Al-sensitive mutant sal3 by a forward genetic screen. Unlike previously reported Al-sensitive mutants that show Al hypersensitivity at the early stage, sal3 mutant displayed hypersensitive to Al at the later stage. We further found that inhibition of root growth by Al in sal3 might be through the inhibition of cell division. We have cloned SAL3 gene and found that it encodes a transcription factor belonging to the GRAS family. Next, we will take a combinatory approach of genetics, physiology, biochemistry and molecular biology to further examine the regulation of Al on the cell division of sal3 roots, and identify SAL3-cooperation transcription factors and downstream Al-resistance genes directly controlled by SAL3 and its interaction factors. Based on all experimental results, we will ultimately elucidate the mechanisms how SAL3 regulates the expression of its downstream Al-resistance genes to modulate root cell division and the associated Al resistance in rice.

酸性土壤占世界可耕地面积的30%以上，酸性土壤的铝毒是限制作物生产的主要因子。目前普遍认为铝毒主要通过抑制根细胞伸长来抑制根的生长，但不清楚铝毒是否也通过抑制细胞分裂来抑制根生长。水稻是一个高抗铝毒的作物，但其高抗铝毒机制还有待作进一步解析。我们前期通过遗传筛选获得一个对铝毒敏感的突变体sal3。与之前报道的铝毒敏感突变体不同的是，该突变体在中后期才表现对铝毒敏感。进一步研究发现，铝毒可能通过抑制sal3的细胞分裂来抑制根的生长。我们克隆了SAL3基因，发现它编码一个GRAS家族成员的转录因子。下一步我们将采用遗传、生理、生化、分子生物学等相关技术手段进一步研究铝毒对sal3细胞分裂的调控，鉴定SAL3的协作转录因子以及它们直接调控的下游抗铝毒基因，最终阐明SAL3通过调控下游抗铝毒基因表达调控细胞分裂，进而调控水稻抗铝毒的机制。

酸性土壤占世界可耕地面积的30%以上，酸性土壤的铝毒是限制作物生产的主要因子。水稻是一个高抗铝毒的作物，但其高抗铝毒机制还有待作进一步解析。我们构建了水稻EMS化学诱变库，通过筛选铝毒敏感或铝抗突变体来克隆和解析水稻抗铝毒新基因。我们获得了一个对铝毒超敏感的突变体sal3 (sensitive to aluminum 3)和一个对铝毒更耐的突变体ral1 (resistance to aluminum 1)。通过全基因组测序并结合标记连锁分析克隆了SAL3和RAL1基因，发现SAL3编码一个GRAS家族成员的转录因子，而RAL1编码4-香豆酸:辅酶A连接酶（4-Coumarate:Coenzyme A ligase）4CL4。通过一系列的生理、生化和遗传实验，我们阐明了SAL3主要通过控制过氧化氢积累来调控水稻对铝毒耐性的作用机制，以及RAL1/4CL4通过影响4-香豆酸和阿魏酸的积累来调节半纤维素之间的交联和对铝离子的结合，从而最终影响水稻抗铝毒能力的新机制。我们的研究结果不仅揭示了调控过氧化氢积累对水稻抗铝毒的重要作用，还揭示了水稻通过分泌羟基桂皮酸主动重塑细胞壁积极应对外在铝毒害的新机制。