Abstract
Auxin response factors (ARFs) bind specifically to auxin response elements (AuxREs) in the promoters of down-stream target genes and play roles in plant responses to diverse environmental factors. Using the latest updated Medicago truncatula reference genome sequence, a comprehensive characterization and analysis of 24 MtARF (M. truncatula ARF) genes were performed. To uncover the basic information and functions of MtARF genes during symbiosis, we analyzed the expression patterns of MtARF genes during the early phase of Sinorhizobium meliloti infection. The systematic analysis indicated that changes in MtARF gene expression occur during these early stages of infection, suggesting a functional role in symbiosis. Furthermore, the roles of MtARF-mediated auxin signaling in symbiosis were tested in the infection resistant mutant (dmi3). The expression responses of MtARFs to S. meliloti infection were attenuated in the mutant compared to wild-type A17. In summary, our results show that changes in MtARF gene expression occur during the response to S. meliloti infection, suggesting that members of this family may have important roles in the symbiotic interaction.
Highlights
The phytohormone auxin is involved in regulating many aspects of plant growth and development, including root system architecture re-establishment under nutrient stress and responses to environmental stimuli
Focusing on the main structural and expression features of Auxin Response Factor (ARF) genes in M. truncatula, which is a model indeterminate legume, helped us to describe the relationship between ARF-mediated auxin signaling and the symbiotic association with nitrogen-fixing bacteria during the early phase of S. meliloti infection
ARF protein relies on the DNA Binding Domain (DBD) to bind to auxin response elements (AuxRE: TGTCTC) in the promoters of auxin responsive genes
Summary
The phytohormone auxin is involved in regulating many aspects of plant growth and development, including root system architecture re-establishment under nutrient stress and responses to environmental stimuli. The transcription of numerous genes are altered rapidly and by auxin treatment (Chung et al, 2011; Molesini et al, 2014) and the Auxin Response Factor (ARF) gene family plays a vital role in response to indole-3-acetic acid (IAA) by regulating expression of down-stream target genes. Recognition of the auxin/indole-3-acetic acid (Aux/IAA) proteins by the auxin transport inhibitor response 1 (TIR1), which is located at the top of SCFTIR1/AFB ubiquitin ligase, accelerates Aux/IAA protein degradation by the 26S proteasome. ARFs, which are inhibited by Aux/IAA, are released and began to modulate the expression of their target genes (Tan et al, 2007)
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