Auxin binding protein 1 (ABP1) is not required for either auxin signaling or Arabidopsis development
Significance The plant hormone auxin is a key regulator of plant growth. It has been hypothesized that some auxin responses are mediated by a candidate auxin receptor called auxin binding protein 1 (ABP1) Support for this hypothesis mainly comes from the analyses of Arabidopsis ABP1 knockdown lines generated by cellular immunization or antisense approaches. However, these approaches are subject to off target effects. As an alternative, we have recovered two new null alleles of abp1. Surprisingly, neither of the mutants exhibits defects in growth and development, or auxin response, indicating that ABP1 does not have a major role in these responses under normal growth conditions. These results require that the role of ABP1 in plant growth and auxin response be reexamined. Auxin binding protein 1 (ABP1) has been studied for decades. It has been suggested that ABP1 functions as an auxin receptor and has an essential role in many developmental processes. Here we present our unexpected findings that ABP1 is neither required for auxin signaling nor necessary for plant development under normal growth conditions. We used our ribozyme based CRISPR technology to generate an Arabidopsis abp1 mutant that contains a 5 bp deletion in the first exon of ABP1, which resulted in a frameshift and introduction of early stop codons. We also identified a T DNA insertion abp1 allele that harbors a T DNA insertion located 27 bp downstream of the ATG start codon in the first exon. We show that the two new abp1 mutants are null alleles. Surprisingly, our new abp1 mutant plants do not display any obvious developmental defects. In fact, the mutant plants are indistinguishable from wild type plants at every developmental stage analyzed. Furthermore, the abp1 plants are not resistant to exogenous auxin. At the molecular level, we find that the induction of known auxin regulated genes is similar in both wild type and abp1 plants in response to auxin treatments. We conclude that ABP1 is not a key component in auxin signaling or Arabidopsis development.
Proceedings of the National Academy of Sciences