Assessing the role of the heterologous expression of the bacterial arsenic efflux pump ACR3 in plant roots: implications for transcriptomics and As accumulation

Transgenic tobacco hairy roots (HR) were developed by expressing the bacterial arsenite efflux pump ACR3, either at the plasma membrane or at the tonoplast of root cells. The aim of the present work was assessing the effect of the heterologous expression of Acr3 on the transcriptome of transgenic HR, in presence (0) or abscence of arsenite, in order to understand the accumulation properties of the roots developed. Our results reveal that transgenic HR expressing ACR3 at the plasma membrane displayed a completely different gene expression profile as compared to control HR (transformed with the empty vector). On the other hand, HR expressing ACR3 at the tonoplast, made through the fusion of the ACR3 protein to the tonoplast integral protein TIP1.1, showed a gene expression profile much more similar to that of control HR. HR clones obtained were named as: Control HR (HR-2, HR-6 and HR-7), ACR3 (ACR3-5, ACR3-7, ACR3-12 and ACR3-14) and TIP-ACR3 (TIP-ACR3-4 and TIP-ACR3-6). Data obtained from RNA extraction and hybridization on Affymetrix microarrays were organized in six different hybridizations: Hybridizations 1, 2 and 3 that compare the different HR, i.e., control HR, ACR3 and TIP-ACR3 in the presence of 0.1 mM As(III) (E0.1) with regard to the same roots exposed to water (E0). On the other side, hybridizations 4 and 5 compare, respectively, the ACR3 and TIP-ACR transgenic roots with control HR, all of them exposed to As(III), whereas hybridization 6 compares ACR3 vs. TIP-ACR3 both exposed to As(III).