Breeding strategy for P-efficient plants

培育磷高效植物是植物育种的重要目标。提高根中有机酸的分泌量是实现这一育种目标的有效途径之一，这可能与缺磷胁迫的响应机制有关。此外，要培育在自然环境中表现出上级生长性能的“真实的磷高效植物”，还应考虑植物-微生物相互作用和植物-土壤相互作用，因为这些相互作用会影响有机酸对磷的溶解效率。1）胡萝卜IPG细胞系和白色羽扇豆中OA的分泌机制IPG（Insoluble phosphate grower）比亲本细胞系能释放大量的柠檬酸盐。利用RNAi技术，我们发现质子泵参与了这种能力。2）拟南芥苹果酸转运蛋白的基因组学研究我们在拟南芥中鉴定了控制铝耐性的QTL，并在该位点上鉴定了一个关键基因，即拟南芥中编码铝响应性苹果酸转运蛋白的AtALMT 1。利用微阵列和遗传学方法，我们发现该基因的表达水平和苹果酸释放能力之间的相关性。我们还研究了AtALMTI的表达和调控，发现AtALMTI的可逆磷酸化参与了这些机制的调控。3）植物-微生物和土壤相互作用我们发现，从碳经济的角度来看，OA的释放应该由micoryiza系统来平衡，因为OA的释放和micoryiza系统对小麦的磷吸收有相加作用。此外，我们还建立了灵敏的、高通量的拟南芥粗粉含量的ICP-MASS定量系统。使用这个系统，我们确定了转基因植物的营养吸收改善。

Development of P-efficient plants, which can grow better than regular crop plants by enhanced ability of P-uptake from soil, would be important targets in plant breeding. Enhancement of organic acid excretion from the root, which seemed to be involved in P-deficiency responsive mechanisms, is one promising approach to realize this breeding target. Furthermore, it should be considered plant-microbial interaction and plant-soil interaction to develop "real P-efficient plants" showing superior growth performance in natural environment because these interactions should affect efficiency of P solublization by excreted OA. From these concepts, we completed research and obtained following findings.1) OA excretion mechanism in Carrot IPG cell line and white lupinThe IPG (Insoluble phosphate grower) can release large amounts of citrate than parental cell line. Using RNAi techniques, we showed proton pumping is involved in this capacity. Also, we found that altered OA metabolism play a key role in OA excretion in white lupin.2) Genomics approach for malate transporter in ArabidopsisWe identified QTL controlling AL tolerance in Arabidopsis and identified a key gene in this locus, namely AtALMT1 encoding a Al-responsive malate transporter in Arabidopsis. Using micro-array and genetic approaches, we found correlation between expression level of the gene and malate release capacity. We also have characterized the AtALMTI expression and regulation and found that involvement of a reversible phosphorylation in regulating these mechanisms.3) Plant-Microbe and Soil interactionsWe found that OA release should be balanced by micoryiza system in terms of carbon economy because OA release and micoryiza system additively contribute on P-uptake in wheat. In addition, we established sensitive and high throughput system for quantifying system for meal contents in Arabidopsis using ICP-MASS. Using this system, we identified improved uptake of nutrients by transgenic plants.