Root type contribution to phosphate nutrition of rice during asymbiosis and interaction with symbiotic fungi.

磷酸盐（Pi）是一种必需的植物常量养分，在大多数土壤中含量很少，这经常限制植物的生长。植物根系对土壤养分资源的挖掘效率直接影响植物的适应性和作物的生产力。植物根系由不同的根类型组成，它们的比例和空间排列决定了根系结构和养分的觅食效率。RTs可以单独响应其非生物和生物土壤微环境，从而不对称地促进植物养分获取。一直以来，科学家和育种家对分类和量化根系结构特征（Rogers and Benfey， 2015年进行了综述）越来越感兴趣，以期“具有最佳根系结构以获取营养的设计作物”（Kong et al., 2014）。然而，令人惊讶的是，RTs的“研究不足”，特别是在缺乏以rt为重点的研究的成年作物中。Paszkowski小组通过研究V8期（开花前）成体水稻植株的RTs，解决了这一知识空白。成年水稻根系由冠根、大侧根和细侧根（分别为CR、LLR、FLR） 3个RTs组成，发育和解剖特征各不相同。每个水稻RT的独特转录特征被揭示，这表明在营养获取中有不同的作用（Gutjahr等人，2015）。植物要么直接获得Pi，要么与自然普遍存在的丛枝菌根（AM）真菌相关。在水稻中，不同的RTs表现出不同程度的定殖，LLR完全定殖，CR部分定殖，而flr仍然未定殖（Gutjahr等，2009）。将水稻根系暴露于有益的AM真菌中导致每个RT转录组的深刻调节，表明它们的功能关系发生了变化。在共生或与AM真菌相互作用过程中，个体RTs对水稻Pi营养的贡献目前尚不清楚，这也是本研究的主要目的。此外，Paszkowski小组最近发现，含有真菌的植物细胞的液泡积累了类似于多磷酸盐储存体的结构（Roth & Paszkowski，未发表），以前没有在高等植物中描述过。因此，定殖和非定殖RTs在组织磷的空间分布和物种形成方面存在差异，这可能会影响植物的营养生理。提出的工作旨在定量和空间上确定π的吸收和分配到组织和细胞池横跨成年水稻根系RTs。在分析，成像和分子遗传学中跨学科技术的独特组合的应用将以前所未有的时空分辨率提供对原位磷通量的洞察。作为一半以上人口的主食，大米是粮食安全的核心。该研究将揭示逆转录酶的功能，对提高植物抗逆性和作物生产力的合理育种方法具有重要意义。

Phosphate (Pi) is an essential plant macronutrient and occurs in scarce amounts in most soils, which frequently limits plant growth. Plant fitness and crop productivity is directly influenced by the plant root system's efficiency in exploring soil nutrient resources. Plant root systems are composed of distinct root types (RTs), and their ratio and spatial arrangement define root system architecture and nutrient foraging efficiency. RTs may individually respond to their abiotic and biotic soil microenvironment, thereby asymmetrically contributing to plant nutrient acquisition. Consistently, there is a growing interest of scientist and breeders in classifying and quantifying root system architectural traits (reviewed in Rogers and Benfey, 2015) towards 'designer crops with optimal root system architecture for nutrient acquisition' (Kong et al., 2014). Surprisingly however, RTs are 'under-investigated' in particular in adult crops where RT-focused research is missing. The Paszkowski group has addressed this gap in knowledge by studying the RTs of adult rice plants at V8 stage (before flowering). The root system of adult rice is composed of three RTs, the crown, large and fine lateral roots (CR, LLR, FLR, respectively) with distinct developmental and anatomical characteristics. Unique transcriptional signatures for each rice RT were revealed, which suggested distinct roles in nutrient acquisition (Gutjahr et al., 2015). Plants acquire Pi either directly or in association with naturally prevalent arbuscular mycorrhizal (AM) fungi. In rice, the different RTs exhibit variable extent of colonization with LLR fully and CR partially colonized, whereas FLRs remain non-colonized (Gutjahr et al., 2009). Exposing rice roots to a beneficial AM fungus led to the profound modulation of each RT transcriptome, indicative of a switch in their functional relationship. The contribution of individual RTs to rice Pi nutrition in asymbiosis or during interaction with AM fungi remains at present unclear and represents the main objective of this proposal. In addition, the Paszkowski group has recently discovered that exclusively vacuoles of fungus-containing plant cells accumulated structures resembling polyphosphate-storage bodies (Roth & Paszkowski, unpublished), previously not described for higher plants. Colonized and non-colonized RTs thus appear to differ in the spatial distribution and speciation of tissue phosphorus, which may impact on the nutritional physiology of the plant. The proposed work aims at quantitatively and spatially determining Pi uptake and partitioning into tissue and cellular pools across the RTs of adult rice root systems. The application of a unique combination of interdisciplinary techniques in analytics, imaging and molecular genetics will deliver an insight into in situ phosphorus fluxes at unprecedented spatio-temporal resolution. As a staple food for more than half of the human population, rice is central for food security. The study will inform about RT functioning, important for rational breeding approaches towards improved plant stress tolerance and crop productivity.