Caracterização morfológica de sorgo superexpressando o gene SbPSTOL1

Abstract

The availability of nutrients in the soil is of great importance for crop establishment and influences plant development and production. Phosphorus (P), indispensable for various biological processes, is a nutrient found in low availability in tropical soils, making it one of the main limiting factors for plant growth. One of the evolutionary mechanisms developed by plants to optimize the absorption of this nutrient is the alteration of root system architecture, aiming at increasing root surface area, which allows for better soil exploration and P absorption. First described in rice, the PSTOL1 gene (PHOSPHORUS STARVATION TOLERANCE1), which encodes a serine/threonine receptor kinase, has been associated with root morphology changes that lead to P stress tolerance. Orthologs of the PSTOL1 gene have been associated with increased root surface area, greater phosphorus accumulation in the shoots, and increased grain production in P-tolerant maize and wheat lines. Association analyses identified several SNPs (Single Nucleotide Polymorphisms) within sorghum PSTOL1 genes (SbPSTOL1) associated with optimized P use associated with changes in root morphology. In transgenic maize events overexpressing SbPSTOL1, increased root system length and surface area, and reduced average root diameter were observed. In this study, transgenic sorghum lines transformed in the P898012 genetic background were used to evaluate the effects of SbPSTOL1 overexpression on root system morphology under phosphorus stress conditions, in soil and in hydroponics. Additionally, physiological characteristics of the shoot and root morphology of the transgenic sorghum events under water stress were evaluated. The events overexpressing SbPSTOL1 showed a trend toward increased surface area and reduced average root diameter under low P conditions, in hydroponic solution and in soil. However, these changes were not consistently observed in in different experiments. Under water stress conditions, the events showed improved photosynthetic rates and reduced leaf temperature, with no significant changes in root morphology. The events overexpressing the SbPSTOL1 gene showed great variation in the evaluated traits related to root morphology in both soil and in nutrient solution. The variation was observed between and within different events. The P898012 sorghum line is reasonably tolerant to water and P stresses which, along with the variation observed in the lines overexpressing the gene, complicates drawing a conclusion about the effect of SbPSTOL1 overexpression on sorghum on tolerance to low P and drought conditions. One consistently observed characteristic was the accumulation of anthocyanins in the panicles of sorghum events grown in a low P soil. In sorghum, anthocyanins are secondary metabolites and increased production of anthocyanins has been associated with abiotic stress tolerance. These results suggest a relationship between SbPSTOL1 and tolerance pathways to abiotic stresses in sorghum.