Understanding the role of auxin biosynthesis and signaling in response to iron deficiency in Arabidopsis thaliana

Abstract

Roots are essential for plant survival, as they play a key role in absorbing water and nutrients from the soil. Plants respond to nutrient deficiencies by changing the morphology and physiology of root system architecture (RSA), a process that is strongly influenced by phytohormones. Among these, auxin is a key phytohormone that regulates many root-related processes, such as vascular differentiation, root hair development, differentiation of root hairs and emergence of lateral roots. Iron (Fe) is an essential micronutrient for all living organisms. Plants respond to Fe limitation through morphological changes which lead to increased root surface area for efficient uptake of Fe. Previous studies have revealed the role of auxin in modulating root development under Fe deficiency, however, the underlying mechanisms remain poorly understood. This study explores the role of Auxin Response Factors (ARFs) and auxin biosynthesis genes in the modulation of root growth responses under Fe deficiency in Arabidopsis thaliana. We found that the expression of ARF5 is strongly induced in response to Fe deficiency and its role is important for root growth under Fe deficiency conditions. In order to investigate the role of ARF5, we used β-estradiol-inducible XVE system to create a rescue line of arf5-2 mutant, which is previously described as sterile. The expression of iron homeostasis genes is affected in the arf5-2 mutants and Perl’s staining also revealed that arf5 mutants accumulated less Fe as compared to wild type plants. Furthermore, we found that the function of TAR2 (tryptophan aminotransferase related 2), an important auxin biosynthesis gene, is critical for proper lateral root growth under -Fe conditions. We also found that low iron-mediated auxin accumulation and root growth responses were significantly impaired in the tar2 mutant. Our data showed that TAR2 is required to reprogram root architecture in response to low Fe conditions. Overall, our results revealed that ARF5 and TAR2 function is important for low Fe-mediated root growth modulation and Fe uptake in Arabidopsis.