DELLA-PIF Regulation of Nitrogen Assimilation: from Arabidopsis Model to Long-Term Translation to Crop Efficiency Gains

上世纪六七十年代著名的谷物“绿色革命”提高了作物产量，避免了饥荒，养活了不断增长的世界人口。水稻和小麦的绿色革命品种是绿色革命的遗传基础。GRV携带突变的生长调节基因，赋予侏儒症，这种侏儒症增加产量，因为它减少了由于“倒伏”（风和雨使植物变平）造成的损失，从而导致绿色革命的产量增加。然而，突变的生长调节基因也导致GRV在吸收以肥料形式提供给它们的氮（N）方面效率较低。因此，没有被GRV吸收的N被消散到更广泛的环境中，对陆地和水生生态系统造成严重破坏，以及加速气候变化的大气温室气体污染。由于当今的高产作物品种仍然依赖于突变矮化基因来获得高产，因此有必要找到开发新的作物品种的方法，这些作物品种保留了GRV矮化的优点，但在氮肥的使用上更有效（提高了氮素利用效率，在这里，我们提出利用遗传模型拟南芥的快速遗传学和分子生物学来进行发现，这将使得未来能够增强GRV NUE。GRV矮化基因引起一类称为DELLA的生长抑制蛋白的积累，并且DELLA也在矮化拟南芥GRV突变体模型gai中积累。积累的DELLA抑制另一类调节蛋白PIF（或光敏色素相互作用因子）的作用。我们最近从拟南芥的研究中获得的初步证据表明，DELLA对PIF的抑制作用可以解释GRV的NUE降低，我们在这个提议中利用的正是这个新颖而令人兴奋的发现。因此，我们将首先进一步检验我们的工作假设，即DELLA和PIF之间的相互作用影响N的同化：在GRV和gai中积累的DELLA反对PIF功能，从而减少N同化。如果该假设是正确的，则DELLA-PIF关系的调节可以提供朝向改善GRV NUE的新途径。我们有以下目标：A。深入了解PIF对拟南芥和水稻氮同化的调节-主要是对PIF在拟南芥和水稻氮代谢和同化调节中的作用进行遗传测试。B。确定DELLA-PIF相互作用如何调节编码硝酸还原酶（NR）的mRNA的丰度，NR是氮同化的关键酶-这是对DELLA-PIF相互作用如何控制编码该酶的基因表达的探索。确定DELLA-PIF相互作用是否也直接影响NR酶本身的丰度和/或比酶活性。确定NUE是否可以增加，尽管保持产量提高矮化。这一点很重要，因为它可以导致作物的发展，保持目前GRV的高产量，但降低环境成本。首先，我们将确定增加PIF活动是否会带来这些好处。然而，由于增加PIF本身在GRV中的活性可能会产生额外的不良后果，因此我们将另外探索其他途径（PIF下游）以提高GRV NUE，同时保留产量提高侏儒症。在我们的战略中，固有的是将拟南芥模型的发现初步翻译为作物（水稻），利用我们在DELLA生物学，模型作物翻译和全基因组序列分析方面的长期综合专业知识。我们的长期目标（未来的建议）是利用在这里获得的基本理解，在水稻和小麦GRV的发展，提高NUE，从而提高全球粮食安全和减少农业环境退化。

The famous cereal 'green revolution' of the 1960s/1970s increased crop yields, averted famine and fed a growing world population. Green Revolution Varieties (GRVs) of rice and wheat were the genetic foundation of the green revolution. GRVs carry mutant growth regulatory genes that confer dwarfism, and this dwarfism increases yield because it reduces loss due to 'lodging' (flattening of plants by wind and rain), hence causing the yield increases of the green revolution. However, the mutant growth regulatory genes also cause GRVs to be less efficient in assimilating the nitrogen (N) supplied to them in the form of fertilizer. As a result, N that is not assimilated by GRVs is dissipated into the wider environment, where it causes severe damage to terrestrial and aquatic ecosystems, together with atmospheric greenhouse-gas pollution that precipitates climate change. Because today's high-yielding crop varieties still depend upon the mutant dwarfing genes for their high yields, it is necessary to find ways of developing new crop varieties that retain the benefits of GRV dwarfism but that are more efficient in their use of N fertilizers (have improved N use efficiency, NUE).Here we propose to exploit the rapid genetics and molecular biology of the genetic model Arabidopsis to make discoveries that will enable future enhancement of GRV NUE. The GRV dwarfing genes cause accumulation of a class of growth inhibitory proteins called DELLAs, and DELLAs also accumulate in the dwarf Arabidopsis GRV mutant model gai. Accumulated DELLAs inhibit the action of another class of regulatory proteins, the PIFs (or Phytochrome Interacting Factors). Our recent preliminary evidence from studies of Arabidopsis suggest that the inhibitory effect of DELLAs on PIFs may explain the reduced NUE of GRVs, and it is this novel and exciting finding that we exploit in this proposal. We will therefore first further test our working hypothesis that interactions between DELLAs and PIFs affect the assimilation of N: that the DELLAs accumulated in GRVs and gai oppose PIF function, thus reducing N assimilation. If this hypothesis is correct, modulation of the DELLA-PIF relationship may provide a novel route towards improving GRV NUE. We have the following objectives: A. Obtain an in-depth understanding of PIF-regulation of Arabidopsis and rice N assimilation - essentially performing genetic tests of the role of PIFs in regulation of N metabolism and assimilation in Arabidopsis and rice. B. Determine how the DELLA-PIF interaction regulates the abundance of mRNA encoding nitrate reductase (NR), a key enzyme in N assimilation - this an exploration of how the DELLA-PIF interaction controls the expression of the gene encoding that enzyme.C. Determine if the DELLA-PIF interaction also directly affects the abundance and/or specific enzymatic activity of the NR enzyme itself.D. Determine if NUE can be increased despite retaining yield-enhancing dwarfism. This is important because it could lead to the development of crops which retain the high yields of current GRVs, but at reduced environmental cost. First, we will determine if increasing PIF activity might confer such benefits. However, because increasing the activity of PIFs themselves in GRVs might have additional unwanted consequences, we will additionally explore other routes (downstream of PIFs) to improving GRV NUE whilst retaining yield-enhancing dwarfism. Inherent in our strategy is initial translation of findings from Arabidopsis model to crop (rice), exploiting our long-standing combined expertise in DELLA biology, model-crop translations, and whole genome sequence analysis. Our long-term aim (future proposals) is to use the fundamental understanding gained here in the development of rice and wheat GRVs having enhanced NUE, thus enhancing global food security and reducing agricultural environmental degradation.