Auxin-signaling F-box protein 4 (AFB4) encoded by At4g24390 shares a significant sequence similarity to auxin receptor TIR1. In this study, we used a combination of physiological, molecular, and genetic approaches to characterize a T-DNA insertion line (GABI-KAT accession no.: 068E01; henceforth designated afb4-1) as a knockout allele. Complete loss-of-function of the AFB4 gene confers defects in many aspects of the plant life cycle including lateral root development, hypocotyl elongation, leaf organogenesis, flowering time, seed formation, and disease resistance to specific phytopathogens. The results presented here argue against the previously proposed mechanism of AFB4 action in negatively controlling auxin sensitivity 1.

Since growth and development of plant organs are largely governed by phytohormones 3, we asked if hormone-mediated responses are modified in afb4-1. Responsiveness to various hormones over a wide range of concentrations was quantified by physiological assays for inhibition of primary root growth or for stimulation of hypocotyl elongation (Supplementary information, Figure S3). Apparently, afb4-1 showed altered sensitivity to exogenous application of 1-aminocyclopropane-1-carboxylic acid (a natural precursor of ethylene), 24-epibrassinolide, gibberellins A3, and abscisic acid. These results implicate AFB4 proteins as important participants in multiple hormonal signaling pathways. On the other hand, afb4-1 did not differ substantially from WT upon treatments with indole acetic acid (IAA), kinetin, and trans-zeatin, suggesting an intact auxin or cytokinin signaling in afb4-1.

Log in or create a free account to read this content

Gain free access to this article, as well as selected content from this journal and more on nature.com

Access through your institution

or

Sign in or create an account
Continue with Google
Continue with ORCiD