Defensa de la planta de arroz frente a hongos patógenos

Author

Sáenz de Navarrete Llabrés, Rafael

Abstract

Plants suffer multiple stresses in nature, either abiotic, biotic or both. Throughout this work, studies have been carried out on rice plants during infection by pathogenic fungi (biotic stress) in a situation of nutritional stress (abiotic stress), and how the response to one type of stress can affect the response to the other. On the one hand, the pathogenic fungus Magnaporthe oryzae has been used to study the plant defense mechanisms against this fungus, responsible for rice pyriculariosis, and genetic components potentially involved in such defense, specifically microRNAs (miRNAs). The miRNAs are a class of small non-coding RNAs that regulate the expression of other genes at a post-transcriptional level. By sequencing the small RNA population of rice tissues, sequences of small RNAs that could be novel rice miRNAs (candidate miRNAs) with a role in plant innate immunity were identified in the laboratory. In this project, resistance/susceptibility phenotypes of CRISPR/Cas9 rice lines were studied for the following candidate miRNAs: miRNA-8, miRNA-64, miRNA-96 and miRNA-203. CRISPR/Cas9 lines for miRNA-8, miRNA-96 and miRNA-203 show increased resistance to the foliar pathogen M. oryzae, whereas CRISPR lines for miRNA-64 show increased susceptibility. The expression patterns of the defense markers OsPBZ1, OsPR1a and OsPR1b explain the phenotype observed in each case. On the other hand, this project has also focused on the effect of phosphate in the regulation of rice plant immunity. Phosphate is one of the most important macromolecules in any biological system and although it is present in the soil in its inorganic form (Pi), its availability is very low.
Therefore, because of the limited capacity of the plant to absorb Pi from the soil, an excessive use of fertilizers is observed in modern agriculture. Previous publications from the laboratory showed that Pi accumulation in the rice plant confers susceptibility against M. oryzae. In view of these results, it was decided to investigate whether Pi-induced susceptibility in rice is observed in interaction with other rice pathogenic fungi, namely the root fungus Fusarium fujikuroi. This fungus is known to produce gibberellins (GA3) that induce excessive stem and root growth. In order to understand the role of phosphate in the interaction plant-F. Fujikuroi, the phenotype of plants grown under phosphate limitation/excess of 3 cultivated rice varieties (Maratelli, Nipponbare and TN67) during infection with F. fujikuroi under 2 phosphate supply conditions (0.025 mM Pi, or Low Pi; 2.5 mM Pi, or High Pi) was analyzed. Additionally, the same study has been performed for miRNA399 overexpressing lines (OE399) known to accumulate Pi under normal growth conditions (sufficient Pi). The miRNA399 regulates Pi uptake by the root, so that an increase in its expression leads to a greater uptake of phosphate from the soil. Phenotypic analysis, in combination with microscopy analysis and quantification of fungal biomass in roots inoculated with F. fujikuroi, has shown that a higher Pi content in the plant favors infection and, therefore, susceptibility of rice to F. fujikuroi. These results are observed both in the different varieties and in miRNA399 overexpressing plants (Pi overaccumulators).

Director

San Segundo de los Mozos, Blanca
Leivar Rico, Pablo

Degree

IQS SE - Undergraduate Program in Biotechnology

Date

2022-09-18