AZG2 transporter plays a key role in auxin/cytokinin lateral root development regulation

Abstract

AZG (AZa-Guanin resistant) is a gene family first described in fungi as purine transporters. Two members of this family, Azg1 and Azg2, are encoded in the Arabidopsis genome. Although they are able to transport purines when functionally expressed in yeast, their physiological role has not been addressed. In the present work, we found evidences suggesting that Azg2 is involved in lateral root development regulation. The function of Azg2 as a cytokinin (CK) transporter could be demonstrated in vivo. AZG2 is expressed in a limited number of cells surrounding the lateral root primordia (LRP). Azg2 promoter activity is present since stage one of LRPs and persist even when the lateral root is emerged. Moreover, initial approaches to AZG2 subcellular localization revealed that the transporter is localized at the plasma membrane. We also found that Azg2 expression is induced by auxins being the transcription factor ARF7 necessary for gene activation. Analysis of transgenic lines showed differences in root architecture. Azg2 KO lines showed more LR density than Wt plants, while overexpression lines (OEs) presented a conditional phenotype with lower LR density. Furthermore, when plants were treated with CKs, the differences between phenotypes increased significantly. KOs lines showed resistance to CKs, whereas an enhanced toxicity in the OEs was observed. All this data encourage us to propose Azg2 as a key factor in cytokinin inhibition of lateral root development.

Fil: Wanke, Dierk. Centre for Molecular Plant Biology; Alemania.