Growth and development are coordinated by an array of intercellular communications. Known plant signaling molecules include phytohormones and hormone peptides. Although both classes can be implicated in the same developmental processes, little is known about the interplay between phytohormone action and peptide signaling within the cellular microenvironment. We show that genes coding for small secretory peptides, designated GOLVEN (GLV), modulate the distribution of the phytohormone auxin. The deregulation of the GLV function impairs the formation of auxin gradients and alters the reorientation of shoots and roots after a gravity stimulus. Specifically, the GLV signal modulates the trafficking dynamics of the auxin efflux carrier PIN-FORMED2 involved in root tropic responses and meristem organization. Our work links the local action of secretory peptides with phytohormone transport.

In recent years, Drosophila melanogaster has emerged as a powerful model for neuronal circuit development, pathology, and function. A major impediment to these studies has been the lack of a genetically encoded, specific, universal, and phenotypically neutral marker of the somatodendritic compartment. We have developed such a marker and show that it is effective and specific in all neuronal populations tested in the peripheral and central nervous system. The marker, which we name DenMark (Dendritic Marker), is a hybrid protein of the mouse protein ICAM5/Telencephalin and the red fluorescent protein mCherry. We show that DenMark is a powerful tool for revealing novel aspects of the neuroanatomy of developing dendrites, identifying previously unknown dendritic arbors, and elucidating neuronal connectivity.T o discover neuronal circuit architecture, genetic tools that specifically mark the pre-and postsynaptic cells and compartments are necessary. Drosophila is a leading genetic model organism in this regard; however, most neuronal circuits remain unmapped. Of particular note is the lack of a universal, phenotypically neutral, and specific marker of the somatodendritic and postsynaptic compartments. Several molecular differences between dendrites and axons, including the presence of different membrane and cytoskeletal proteins in neuronal subregions, have been identified (1, 2). Drosophila neurons exhibit the major kinds of compartmentalization present in mammalian neurons and the fly has emerged as a powerful system to study the establishment and maintenance of neuronal connections (3, 4). Almost all studies of neuronal circuits in the fly have relied on genetic markers such as CD8::GFP that outline the morphology of entire cells rather than particular subcellular compartments (5), as well as presynaptic markers such as Synaptotagmin, Synaptobrevin, and Bruchpilot GFP fusion proteins (6-11). However, more accurate identification and mapping of novel neuronal circuits has been hampered by the lack of a genetically encoded and phenotypically neutral dendritic marker. Over the years, many such markers have been proposed and several were recently examined (12), namely MAP2 (13, 14), Nod::YFP (4, 15-18), Homer::GFP (19), and DSCAM17.1::GFP (20, 21). The analysis of these markers reveals that none of them labels the entire somatodendritic field. Furthermore, it remains unclear whether the markers tested are neutral with respect to dendritic morphology.Intercellular adhesion molecules (ICAMs) mediate neuronal migration, axon elongation, and fasciculation, synaptogenesis, and synaptic plasticity (22). ICAM5, or Telencephalin, is a 130-kDa type I transmembrane glycoprotein comprising a characteristic extracellular domain, a single transmembrane region, and a short cytoplasmic region (23). The expression of ICAM5 is restricted to the mammalian brain telencephalon (24) but there is no homolog in invertebrates and lower vertebrates. The developmental appearance of ICAM5 parallels the time of dendritic elongation, branching, a...

The GOLVEN (GLV)/ROOT GROWTH FACTORS/CLE-Like small signaling peptide family is encoded by 11 genes in Arabidopsis (Arabidopsis thaliana). Some of them have already been shown to control root meristem maintenance, auxin fluxes, and gravitropic responses. As a basis for the detailed analysis of their function, we determined the expression domains for each of the 11 GLV genes with promoter-reporter lines. Although they are collectively active in all examined plant parts, GLV genes have highly specific transcription patterns, generally restricted to very few cells or cell types in the root and shoot and in vegetative and reproductive tissues. GLV functions were further investigated with the comparative analysis of root phenotypes induced by gain-and loss-of-function mutants or in treatments with GLV-derived synthetic peptides. We identified functional classes that relate to the gene expression domains in the primary root and suggest that different GLV signals trigger distinct downstream pathways. Interestingly, GLV genes transcribed at the early stages of lateral root development strongly inhibited root branching when overexpressed. Furthermore, transcription patterns together with mutant phenotypes pointed to the involvement of GLV4 and GLV8 in root hair formation. Overall, our data suggest that nine GLV genes form three subgroups according to their expression and function within the root and offer a comprehensive framework to study the role of the GLV signaling peptides in plant development.