Análise funcional dos genes SbMATE1 e SbMATE7 quanto à tolerância ao alumínio em sorgo

• Ano de defesa: 2018
• Autor(a) principal: Matheus Thomaz Nogueira Silva Lima
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: Tolerância ao alumínio; Solos ácidos; Sorghum bicolor; MATE; Genética
• Link de acesso: http://hdl.handle.net/1843/BUOS-B7FLE9

Agricultural production on acid soils is compromised by aluminum (Al) toxicity, which damages the root system leading to mineral nutrient deficiency and enhanced drought stress. Considering that approximately 50% of the cultivated soils in the world are acidic, developing crops that are more tolerant to aluminum toxicity is important for global food security. SbMATE is an Alactivated citrate transporter that is expressed in the root apices of Al-tolerant sorghum genotypes, which confers sorghum aluminum tolerance via a mechanism based on a citrate exudation. The gene encoding SbMATE is located on sorghum chromosome 3 and controls most of the Al tolerance phenotype in sorghum. SbMATE encodes a membrane citrate transporter, with 12 predicted transmembrane domains. This study was aimed at functionally characterizing two MATE genes, SbMATE1 and SbMATE7. These genes are homologs to SbMATE, are hypothesized to underlie an analogous mechanism of aluminum tolerance based on Al-activated citrate release. Candidate genes were obtained based on RNA-Seq data, and from protein sequence similarity analyses (BLASTp) in sorghum using SbMATE as a query. In silico protein structure modeling allowed the identification of 12 transmembrane domains for the SbMATE1 and SbMATE7 proteins. A gene structure with 13 exons and 12 introns was also conserved between both genes. Expression profiling was performed with total RNA isolated from root apices (first centimeter) subjected to a nutrient solution without (0 M) and with aluminum (27 M) for 1, 3 and 5 days, roots and leaves, for 5 days with two Al-tolerant lines, SC566 and SC283, and two Al-sensitive lines, BR012 and BR007. SbMATE7 expression decreased with time in the genotype SC566, which is the opposite behavior compared to SbMATE. For SbMATE7 a lower expression was observed in aluminum sensitive genotypes when compared to the tolerant ones. SbMATE1 shows a temporal expression induction by aluminum in Al-sensitive genotypes in comparison to tolerant ones. In the roots, the Al-induction is statistically significant for BR012 in the fifth day of stress. Phylogenetic analysis was undertaken, based on the maximum likelihood method, including SbMATE1, SbMATE7 and other MATE proteins described in the literature. SbMATE7 is present in a clade containing proteins associated with aluminum tolerance. SbMATE1 is present in a clade with other MATE proteins associated with iron homeostasis and aluminum tolerance. Arabidopsis transgenic lines superexpressing SbMATE7 from the tolerant genotype SC566 showed a trend for increased Al tolerance compared to the non-transformed control, which was, however not statistically significant. This was measured via inhibition of root growth in a nutrient solution containing aluminum. The values were 45,46% for event 5 and 11,79% for event 9. This suggests a positive effect of SbMATE7 expression over the tolerance to aluminum, which has an expression profile, structure and phylogenetic patterns closer to proteins that confers Al-tolerance. However, an effect for SbMATE7 on Al tolerance needs to be confirmed with homozygous lines, which should reduce the experimental error. Physiological characterization and subcellular localization studies need to be undertaken to help clarify a possible relationship between protein structure and aluminum tolerance conferred by SbMATE1 and SbMATE7. Future findings are expected to open novel perspectives for increasing sorghum yields on acid soils, expanding to what is already provided by SbMATE