Investigating the role of microRNAs in enabling nodulation

为了确保粮食安全，我们需要作物不仅能承受植物胁迫的不利影响，而且还能提高产量。为了应对土壤中的低氮水平，豆科植物与根瘤中的根瘤菌土壤细菌形成共生关系，从而能够从大气中固定氮。然而，细菌入侵呈现出某种进化上的悖论，因为它需要植物允许微生物入侵，而不提供被真正病原体利用的后门。据认为，豆科植物能够特异性地识别根瘤菌，并选择性地抑制防御反应以允许定植。微小RNA（miRNAs）被认为是豆科植物从防御反应向抑制反应转变的重要介质。为了更好地了解豆类和非豆类之间的差异，使前者能够进行转录，我们将使用RNAseq分析非豆类（包括拟南芥）和豆类（包括蒺藜苜蓿）在响应根瘤菌和进行防御反应时的转录组表达。对这些数据的分析，结合miR位点的预测，将使我们能够对miR在物种间防御与增殖中的作用做出假设。我们的目的是确定miR的调控作用是特定的，并在体外循环过程中保守。然后，我们的目标是使用转基因植物表达GFP特异性地在表皮，皮层或周皮和荧光激活细胞分选（FACS）分离这些单细胞类型。因此，我们可以测试miR调控预测，并询问共生与防御反应发生在什么水平的组织特异性。这将使我们深入了解哪些基因和细胞类型（特别关注miRNA）对于调节植物共生和防御之间的平衡至关重要。

To ensure food security we need crops that not only withstand detrimental effects of plant stresses but also have higher productivity. To deal with low nitrogen levels in soil, leguminous plants form a symbiosis with rhizobia soil bacteria in root nodules, enabling nitrogen fixation from the atmosphere. However, nodulation presents something of an evolutionary paradox because it requires a plant to permit invasion by a microorganism without providing a backdoor to be exploited by a bona fide pathogen. It is thought that legumes are able to specifically recognise rhizobia and selectively supress defence responses to allow colonization. Micro RNAs (miRNAs) are believed to be important mediators of the transition from defence responses to nodulation in legumes. In order to better understand the differences between legumes and non-legumes that allow the former to nodulate, we will use RNAseq to analyse transcriptome expression of non-legumes, including Arabidopsis thaliana, and legumes, including Medicago truncatula, when responding to rhizobia and when undergoing defence responses. Analysis of this data, in combination with miR site predictions, will enable us to make hypotheses about the roles of miRs in defense vs. nodulation across species. We aim to identify miRs whose regulatory action is specific to and conserved during nodulation. We then aim to use transgenic plants expression GFP specifically in the epidermis, cortex or pericycle and Fluorescence Activated Cell Sorting (FACS) to isolate these single cell types. We can thus test the miR-regulatory predictions and ask at what level of tissue specificity the symbiosis vs. defense responses occur. This will give us a deep understanding of which genes and cell types (with particular attention on miRNAs) are important for regulating the balance between symbiosis and defence in plants.