How candidate genes respond to aluminum toxicity in Citrus x limonia Osbeck?

In acidic soils, toxic aluminum (Al) inhibits root growth of sensitive species, including Citrus plants. In the Americas, rainfed Citrus plantations are highly dependent on unique rootstocks, such as the 'Mandarin' lime (Citrus x limonia Osbeck), which is tolerant to drought although sensitive to Al. It requires yearly lime application to grow on soils that are acidic (pH < 5.0) and rich in Al, especially in central and southeastern areas of Brazil. Despite this scenario, genes that are modulated by Al have not yet been searched in this species. Root apices of 'Mandarin' lime plants grown for 60 days in nutrient solutions either with 1480 mu M Al3+ or 0 mu M Al3+ were analyzed by RNA-seq, and differentially expressed candidate genes were validated by qRT-PCR. We highlight the transcriptional up-regulation of citrate synthase and citrate exudation by MATE (multidrug and toxic compound exudation) channels. Genes related to specialized metabolism, pectin methylesterification, auxin response, defense to biotic and abiotic stresses, cell division, suberin deposition, and nitrate uptake were also up-regulated by Al. The overview of up-regulated genes in 'Mandarin' lime not only validates its sensitivity to Al, but also points out targets for future research of Al resistance in this rootstock.

Automated summary

In acidic soils, toxic aluminum (Al) inhibits root growth of sensitive species, including Citrus plants. This study identified genes that are modulated by Al in the tolerant 'Mandarin' lime rootstock, highlighting the up-regulation of citrate synthase and citrate exudation by MATE channels. Genes related to specialized metabolism, pectin methylesterification, auxin response, defense to biotic and abiotic stresses, cell division, suberin deposition, and nitrate uptake were also up-regulated by Al, providing targets for future research on Al resistance in this rootstock.