Banca de DEFESA: JOSÉ NIVALDO DE OLIVEIRA SÁTIRO

Use of humic acid to identify differentially expressed biotechnological targets involved in growth promotion in rice plants.

Humic acid. Transcriptome. Gene expression. Rice.

The use of biostimulants has gained scientific and commercial visibility and is considered a promising technique to improve the growth and development of several plant species. Among the biostimulant substances, humic acid (HA) has been the subject of study in agriculture due to its role in the acquisition of nutrients and water through gene modulation. Despite the established evidence on the effects of humic acid, many transcriptional aspects still require elucidation. The research developed in this thesis seeks to contribute to the understanding of the molecular and physiological mechanisms through the use of large-scale RNA sequencing (RNA-Seq). To this end, the following questions were raised: (i) what concentrations of humic acid are capable of stimulating the growth of the rice root system; (ii) whether relative gene expression is altered with exposure to humic acid; (iii) whether the bioactive effect of humic acid can reveal genes with biotechnological potential for growth promotion in rice plants. In order to verify these questions, the objective of this research was to conduct experiments with the ultimate purpose of using HA to identify biotechnological targets for growth promotion in Nipponbare rice plants. The specific objectives were: a) to establish the optimal concentration of humic acid for the greatest stimulation of root system growth; b) to establish the time of exposure to humic acid that shows transcriptional response; c) to determine the differentially expressed genes through large-scale gene expression analysis (RNA-seq); d) to group the differentially expressed genes through their ontologies to evaluate the processes or pathways that are preferentially affected by treatment with humic acids. The data obtained suggest that the dose of 80 mg L-1 HA alters the morphological parameters of the roots and the biomass of rice plants in a hydroponic system. This dose provided a rapid and delayed gene induction, in 4h and 72h of exposure to the plants, respectively. Sequencing identified 239 differentially expressed genes (DEG) in the root and 55 genes in the shoot of rice after 4 h of exposure to HA. In addition, most genes were downregulated in both tissues (root and shoot). Functional enrichment analysis allowed us to understand the functional profile of 91 DEG in the root and 5 DEG in the shoot. In addition, genes of the DUF family were identified, responsible for encoding proteins with functions not yet known. These results provide new insights for the development of future research, aiming to obtain plants adapted to adverse conditions.