The geneMACCHI-BOU 4/ENHANCER OF PINOIDencodes a NPH3-like protein and reveals similarities between organogenesis and phototropism at the molecular level

Abstract

Intercellular transport of the phytohormone auxin is a significant factor for plant organogenesis. To investigate molecular mechanisms by which auxin controls organogenesis, we analyzed the macchi-bou 4 (mab4) mutant identified as an enhancer of pinoid (pid). Although mab4 and pid single mutants displayed relatively mild cotyledon phenotypes, pid mab4 double mutants completely lacked cotyledons. We found that MAB4 was identical to ENHANCER OF PINOID (ENP), which has been suggested to control PIN1 polarity in cotyledon primordia. MAB4/ENP encodes a novel protein, which belongs to the NON-PHOTOTROPIC HYPOCOTYL 3 (NPH3) family thought to function as a signal transducer in phototropism and control lateral translocation of auxin. MAB4/ENP mRNA was detected in the protodermal cell layer of the embryo and the meristem L1 layer at the site of organ initiation. In the mab4 embryo, the abundance of PIN1:GFP was severely decreased at the plasma membrane in the protodermal cell layer. In addition, subcellular localization analyses indicated that MAB4/ENP resides on a subpopulation of endosomes as well as on unidentified intracellular compartments. These results indicate that MAB4/ENP is involved in polar auxin transport in organogenesis.

NPY genes and AGC kinases define two key steps in auxin-mediated organogenesis in Arabidopsis

“…Inactivation of one or more NPY1 homologs in npy1 background leads to the formation of pin-like inflorescences, a phenotype observed in pid and yuc1 yuc4 npy1 triple mutants (18). Furthermore, we show that inactivation of the 3 closest PID homologs in the pid background completely abolishes the formation of cotyledons, a phenotype that is also observed in yuc1 yuc4 pid triple mutants (18) and npy1 pid double mutants (18,19). Our analyses establish that members of YUC, NPY1, and PID families participate in a linear pathway in regulating auxin-mediated organogenesis in Arabidopsis and NPY genes and PID-like AGC kinases define 2 essential steps in the pathway.…”

“…Mutations in NPY1 greatly enhanced the phenotypes of yuc1 yuc4 double mutants (18) and pid mutants (18,19), but npy1 itself does not have dramatic developmental defects. It is likely that a subset of the NPY1 homologs has at least partially overlapping functions with NPY1.…”

“…Mutant npy1 is allelic to enhancer of pinoid 1 (enp1) and macchi-bou 4 (mab4) (19,20), which failed to develop cotyledons in the pid background. NPY1/ENP1/MAB4 encodes a plant-specific protein that contains a BTB (Bric-a-brac, Tramtrack, Broad-complex) domain at the N-terminal region and an NPH3 (NON-PHOTOTROPIC HYPOCOTYL 3) domain in the middle.…”

Of Blades and Branches: Understanding and Expanding the Arabidopsis Ad/Abaxial Regulatory Network through Target Gene Identification

“…Thus, NPH3-like proteins and AGC3 kinases together determine the direction of auxin transport. The NPY genes (there are five of them) are a subset of NPH3-like genes that together with the WAG and PID AGC3 kinases (there are four of them) are required for lateral organ outgrowth (Furutani et al 2007(Furutani et al , 2011. REV-OLUTA activates, probably directly, transcription of NPY1 and WAG1, whereas KANADI represses, probably indirectly, NPY3 and WAG2 (T Huang et al, unpubl.).…”

Higher plants use LOV to perceive blue light

“…Moreover, while the LOV domains of phototropins have rapid photocycles, the LOV domains of ZTL family members hardly dark revert at all. [49,50]. Given that phototropin signaling modulates auxin transport it will be interesting to study this connection further.…”