Rta1 lipid transporter involved in aluminum and acid tolerance in Cryptococcus humicola

Aluminum (Al) toxicity is a major limiting factor for crop growth in acidic soils worldwide. Therefore, it is necessary to study Al-tolerance mechanisms. Cryptococcus humicola is a good candidate for Al-tolerance research due to its high ability for Al tolerance. qRT-CR analysis revealed that the expression of the RTA1 gene was upregulated approximately 18-fold in C. humicola under 50 mM Al stress. In this study, we investigated the role of the Rta1 lipid transport protein of C. humicola in acid and Al resistance. The Rta1 lipid transport protein was predicted to be a membrane protein with seven transmembrane structural domains, with low homology to other fungi but highly similar secondary structures. RTA1 mutant and transgenic yeast strains were constructed. Under normal conditions, the RTA1 mutant tended to aggregate into clusters compared with the wild type, but the clustering of the RTA1 mutant disappeared under Al stress. The growth of the RTA1 mutant and transgenic yeast on plates and in liquid culture medium revealed that the Rta1 lipid transporter protein could help C. humicola resist acidic and Al stress. After 50 mM Al treatment, the malondialdehyde content of the RTA1 mutant was greater than that of the wild type, suggesting that membrane lipid damage was more severe in the RTA1 mutant than in the wild type. The above results suggest that the Rta1 lipid transporter protein may affect cellular membrane function and thus lead to increased acid and Al tolerance in cells.