FORKED1 encodes a PH domain protein that is required for PIN1 localization in developing leaf veins

Abstract

SUMMARYThe formation of Arabidopsis leaf veins is believed to require canalization of auxin into discrete and continuous cell files to generate a highly reproducible branched and reticulate pattern. During canalization, incipient veins become preferred routes for auxin transport through expression and asymmetric localization of the PINFORMED1 (PIN1) auxin efflux protein: PIN1 expression narrows from a group of cells to a single cell file, and localization of PIN1 protein becomes polarized to the cell membrane facing a previously formed vein. The shift in PIN1 localization is believed to require active vesicle cycling and be auxin-dependent, generating an autoregulatory loop. Previously, we have shown that fkd1 mutant leaves have an open vein pattern that lacks distal vein meeting. Here, we identify FKD1 as encoding a pleckstrin homology domain-and DUF828-containing protein. A fusion of the FKD1 promoter and the GUS reporter gene was expressed in vascular tissue throughout the plant, and its expression in incipient veins in leaves narrows in a manner similar to that of PIN1. FKD1 expression in roots and leaves can be altered by changes to auxin response and auxin transport. In the absence of FKD1, PIN1::GFP narrowing to incipient veins is delayed, and localization to the apical cell face is infrequent. The lack of apical PIN1 localization correlates with the failure of newly forming veins to connect distally with previously formed veins. Our data suggest that FKD1 influences PIN1 localization in an auxindependent manner, and we propose that it represents a key component of the auxin canalization pathway.

Increase in vascular pattern complexity caused by mutations in LHY and CCA1 in Arabidopsis thaliana under continuous light

“…Images of the leaves were captured with a microscope (Leica EZ 4D) and inspected. The vascular patterns in van3-2 and fkd1 were simpler than those of wild-type plants, as reported previously (Hou et al 2010;Koizumi et al 2000;Naramoto et al 2009; Figure 1A, C, and D).…”

“…This tendency was not observed in seedlings grown for 7 or 10 days (Table 1 and Figures 3 and 4). In contrast, as reported previously (Hou et al 2010;Koizumi et al 2000;Naramoto et al 2009), the numbers of areoles and branch points in van3-2 and fkd1 plants grown for 7, 10, and 14 days were much smaller compared to those of the wild type (Table 1 and Figures 2-4). The numbers of free ends in van3-2 and fkd1 plants grown for 7 or 10 days were greater than that in the wild type (Table 1 and Figures 3 and 4).…”

“…Several mutations have been reported that simplify the vascular pattern in Arabidopsis leaves (Hou et al 2010;Koizumi et al 2000;Naramoto et al 2009). In contrast, no mutant has been described that has a more complicated vascular pattern than that of the wild type.…”

“…fkd1 was isolated as an abnormal vein pattern mutant (Steynen et al 2003). FKD1 was shown to be the same protein as VAN3 binding protein (VAB) and has thus been proposed to be related to vascular pattern formation via the auxin-dependent regulation of PIN localization (Hou et al 2010;Naramoto et al 2009). …”

The VASCULATURE COMPLEXITY AND CONNECTIVITY Gene Encodes a Plant-Specific Protein Required for Embryo Provasculature Development

“…Auxin canalization is achieved by the expression and polarized localization of the auxin efflux carrier PIN FORMED1 (PIN1) in procambial cells (Sauer et al, 2006;Scarpella et al, 2006). Defects in the proper polar localization of PIN1, such as those in the forked1 and scarface1 mutants, result in abnormal vein patterns and vascular discontinuities in cotyledons and leaves (Deyholos et al, 2000;Hou et al, 2010). Consistent with the role of membrane sterols in the localization of auxin transporters at the plasma membrane (Willemsen et al, 2003;Men et al, 2008;Yang et al, 2013), many sterol biosynthetic mutants show altered auxin distribution and vein pattern defects (Souter et al, 2002;Carland et al, 2010;Pullen et al, 2010).…”