Breeding strategy for P-efficient plants

培育磷高效植株，通过提高土壤对磷的吸收能力，使其比普通作物生长得更好，将是植物育种的重要目标。促进根部有机酸的分泌似乎与缺磷反应机制有关，是实现这一育种目标的一条有希望的途径。此外，要培育在自然环境中表现出优异生长性能的“真正的磷高效植物”，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排泄的OA对磷的溶解效率。1)胡萝卜IPG细胞系和白羽扇豆中的OA分泌机制IPG(不溶性磷酸盐生长菌)比亲本细胞系能够释放大量柠檬酸。利用RNAi技术，我们证明了质子泵浦与这种能力有关。2)拟南芥苹果酸转运蛋白的基因组学方法我们在拟南芥中发现了控制耐铝的QTL，并在该基因座上发现了一个编码苹果酸铝转运蛋白的关键基因AtALMT1。利用基因芯片和遗传方法，我们发现该基因的表达水平与苹果酸释放量之间存在相关性。我们还对AtALMTI的表达和调控进行了表征，发现可逆的磷酸化参与了这些机制的调控。3)植物-微生物和土壤的相互作用我们发现，从碳经济的角度来看，应该通过微生物系统来平衡OA的释放，因为OA的释放和Microoryiza系统对小麦的P吸收是相加的。此外，我们还建立了灵敏、高通量的电感耦合等离子体质谱定量系统。利用这个系统，我们发现转基因植物对营养物质的吸收有所改善。

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.