Abordagens genético-genômicas para identificação e validação de QTLs de tolerância ao alumínio em milho

Abstract

The Al toxicity is a major constraint for root growth on acid soils, leading to serious limitations in crop production. These soils are widely distributed in tropical and subtropical regions, comprising about 50% of arable land on the planet. The development of Al tolerant genotypes is a sustainable alternative to overcome the limitations caused by acid soils.Aluminum tolerance is a complex trait in maize, possibly involving multiple genes and mechanisms that are still not well understood. In our current work, 36,147 SNPs based on genotyping-by-sequencing technology (GBS), 39 SSRs and three candidate genes wereassessed in a population of RILs derived from a cross between two maize lines highly contrasting for Al tolerance. Marker-trait associations were performed using generalized linear models (GLM) and multiple interval mapping (MIM), been identified eight QTL on chromosomes 2, 3, 4, 5, 6 and 8. A major QTL, explaining 22% of the genotypic variance ofAl tolerance, was mapped on chromosome 6 (bin 6.00), confirming previously published results. The candidate gene ZmMATE1 was mapped in this region, as well as two expression QTL (eQTL) flanking the target gene, which were considered as cis eQTL. This genomic region was transferred to maize near-isogenic line, resulting in a two-fold increase of Al tolerance associated with an enhanced ZmMATE1 expression. These results validated the QTL6 as capable to improve Al tolerance in maize. The candidate gene ZmMATE2 was colocated with the Al tolerance QTL5.1, but it was not validated in the lines the maize NILs. However, a trans eQTL explaining 24% of genotypic variation of ZmMATE2 expression was mapped to chromosome 3. A high density of GBS-based markers allowed a considerable precision improvement of QTL identified, whose confidence intervals were restricted from 1.7 to 31.7 Mb. Integration of genetic map information with physical genomic position was possible due to the alignment of SNP sequences in the reference maize genome, which is another great advantage of these GBS-based markers. Thus, the results generated here can be directly applied on marker-assisted breeding to develop maize genotypes with improved Al tolerance. Moreover, the other QTL regions combined with in silico search allowed to select new candidate genes to be target for advanced studies, which can contribute to a better understanding of the mechanisms and genes involved in maize Al tolerance.