Caracterização genética e morfo-fisiológica de linhagens e híbridos transgênicos de milho expressando o gene SbMATE de sorgo

Abstract

Aluminum (Al) toxicity is a limiting factor for crop production on acid soils. Under these conditions, the rhizotoxic form of Al, Al3+, is solubilized into the soil solution inhibiting root growth, thus reducing water and nutrient uptake. An important mechanism of Al tolerance in plants is based on the release of organic acids (e.g. malate and citrate) by the root apex, which forms non-toxic complexes with Al3+. Genes responsible for Al tolerance have been identified and characterized, such as SbMATE, a major Al tolerance gene in sorghum that encodes an Al-activated citrate transporter, and ZmMATE1, the functional homolog of SbMATE in maize. Considering that heterologous expression of SbMATE increased Al tolerance in Arabidopsis and barley, transgenic maize lines expressing SbMATE were generated. The transgenic events were generated using the temperate hybrid Hi II, and introgressed into L3, a maize line belonging to the Embrapa Maize and Sorghum breeding program. The objective of this study was to evaluate Al tolerance, transgene expression and root morphology of transgenic inbred lines and hybrids expressing SbMATE controlled by the ubiquitin promoter. The transgenic L3 showed high expression levels of SbMATE gene, which was induced after 24 hours of Al treatment in roots and root apices. Compared with the non-transgenic line, Al tolerance assessed in hydroponics was also enhanced in the transgenic L3, which had more profused root development in the sub-superficial soil layer with 15% of Al saturation. The maize hybrids containing one allele of SbMATE were more tolerant than the non-transgenic hybrids and their Al tolerance exceeded the midparent mean. However, the hybrids were less Al tolerant than the parental transgenic line, indicating a partially dominant effect of the transgene. For most of the genotypes, SbMATE expression in the hybrids was similar to the lines, suggesting that transgene expression was not influenced by its allelic dosage. Additionally, the presence of the heterologous SbMATE transgene does not seem to reduce the expression of ZmMATE1, or to change the root morphology in hydroponics. Thus, our current results indicate that transgenic technology using SbMATE can be a used to improve Al tolerance in maize and in other crops, opening new avenues to guarantee yield stability on acid soils.