Plant Cell Rep (2009) 28:1747–1758 Fig. 8 Multiple amino acid sequence alignment of the auxin-binding protein 1 (ABP1) in land plants. Sequences were aligned using MAFFT L-INSI (Katoh et al. 2005). Black shaded boxes highlight identical residues. Grey shaded boxes mark similar residues. Gaps are marked by dashes in the alignment. Within the consensus line conserved amino acids are depicted in capital letters. The amino acids belonging to the KDEL retention sequence are highlighted by red squares 1755 anti-ABP1 antibodies, nicely conﬁrming earlier ﬁndings on corn (Jones and Venis 1989). This result suggests that there are other ABP1-related proteins or proteins sharing epi- topes with ABP1 and which are present not only in Funaria but also in higher land plants. These proteins might be part of the auxin metabolising enzymes or transporters presumably being conserved across species, like the GH3 proteins (Ludwig-Mu¨ ller et al. 2009). Based on these results, it is also tempting to speculate that these proteins may be the molecular imprint of a primitive auxin sensing machinery. Retention of these proteins in the ER of vas- cular plants may have evolved much later as a safeguard 123