Abstract
ABSTRACTThe Arabidopsis thaliana Fasciclin like arabinogalactan protein 4 (FLA4) locus is required for normal root growth in a linear genetic pathway with the FEI1 and FEI2 loci coding for receptor-like kinases. The two Fas1 domains of FLA4 are conserved among angiosperms but only the C-terminal Fas1 domain is required for genetic function. We show that at low salt deletion of the N-terminal Fas1 domain of transgenic FLA4 leads to enhanced root elongation compared to the tandem Fas1 wild type version. Modeling the hypothetical interaction between FLA4 and FEI1 we show that the predicted interaction is predominantly involving the C-terminal Fas1 domain. Relative conformational mobility between the two FLA4 Fas1 domains might regulate the interaction with the FEI receptor kinases. We therefore speculate that the FLA4 FEI complex might be a sensor for environmental conditions in the apoplast.
Highlights
The Arabidopsis thaliana Fasciclin like arabinogalactan protein 4 (FLA4) locus is required for normal root growth in a linear genetic pathway with the FEI1 and FEI2 loci coding for receptor-like kinases
The fasciclin 1 (Fas1) domain is a structural feature of many extracellular proteins in all clades of life and has been implicated with adhesion to and signalling influenced by the extracellular matrix.[1,2,3,4,5]
The FLA4 protein encoded by the Arabidopsis thaliana Salt Overly Sensitive 5 (SOS5) locus is required for normal root growth and salt tolerance and acts in a linear genetic pathway with two leucine rich repeat receptor kinases encoding loci named FEI1 and FEI2.6–8 Sequence searches suggest that every angiosperm genome contains at least one putative orthologue of FLA4 containing both, the N-proximal Fas[1] and the C-proximal Fas[1,2] domain in tandem
Summary
The Arabidopsis thaliana Fasciclin like arabinogalactan protein 4 (FLA4) locus is required for normal root growth in a linear genetic pathway with the FEI1 and FEI2 loci coding for receptor-like kinases. By contrast, when the NaCl concentration exceeded 50 mM, the full length UBQ:F4C(sos5-1) and the truncated UBQ:F4CΔFas[1] (sos5-1) lines behaved identically which indicates that under these conditions, the N-terminal Fas[1] domain is neutral for the role of FLA4 in root growth.
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