Proc. Natl Acad. Sci. USA 112, 2275—2280 (2015)

Decades of research by multiple groups have accumulated evidence that the plant hormone auxin is perceived by a pair of coexisting receptors: ABP1, a weakly-secreted unusual cell surface protein that controls rapid non-transcriptional events, and TIR1, a nuclear F-box involved in the ubiquitin-mediated degradation of transcriptional repressors. Recent work led by Yunde Zhao and Mark Estelle challenges this model and questions the importance of ABP1 in auxin signalling.

Due to the embryo lethality of one early-described null mutant, previous research on ABP1 has been performed using less ideal approaches. This new work uses the latest CRISPR technology to generate a precise genomic deletion in the ABP1 gene, and in addition the authors obtained a new insertion line. Both are confirmed to be null mutants. Unexpectedly, both are viable, show none of the described auxin-related developmental phenotypes, are not auxin resistant and do not have altered hormonal responses at the molecular level.

Although the most obvious conclusion is that ABP1 is dispensable for auxin signalling, the reasons for this stunning discrepancy with previous work are not fully understood yet. Secondary mutations, off-target and compensation effects are suspected. Nevertheless, in the light of these new results, there is an urgent need to re-examine the function of ABP1 in plant growth and development.