To identify novel genes engaged in plant epidermal development, we characterized the phenotypic variability of rosette leaf epidermis of 310 sequenced Arabidopsis thaliana accessions, focusing on trichome shape and distribution, compositional characteristics of the trichome cell wall, and histologically detectable metal ion distribution. Some of these traits correlated with cLimate parameters of our accession's locations of origin, suggesting environmental selection. A novel metal deposition pattern in stomatal guard cells was observed in some accessions. Subsequent GWAS analysis identified 1546 loci with protein sequence-altering SNPs associated with one or more traits, including 5 genes with previously reported relevant mutant phenotypes and 80 additional genes with known or predicted roles in relevant developmental and cellular processes. Some candidates, including GFS9/TT9, exhibited environmentally correlated allele distribution. Several large gene famiLies, namely DUF674, DUF784, DUF1262, DUF1985, DUF3741, cytochrome P450, receptor-Like kinases, Cys/His-rich C1 domain proteins and formins were overrepresented among the candidates for various traits, suggesting epidermal development-related functions. A possible participation of formins in guard cell metal deposition was supported by observations in available loss of function mutants. Screening of candidate gene lists against the STRING interactome database uncovered several predominantly nuclear protein interaction networks with possible novel roles in epidermal development.

• Keywords
• Arabidopsis thaliana, BioClim, GWAS, guard cell, metal accumulation, phenotypic variability, trichome,
• MeSH
• Arabidopsis * genetics   metabolism   growth & development   MeSH
• Genome-Wide Association Study * MeSH
• Plant Epidermis * metabolism   genetics   growth & development   MeSH
• Phenotype MeSH
• Polymorphism, Single Nucleotide genetics   MeSH
• Metals * metabolism   MeSH
• Plant Leaves * genetics   metabolism   growth & development   MeSH
• Arabidopsis Proteins genetics   metabolism   MeSH
• Gene Expression Regulation, Plant MeSH
• Genes, Plant * MeSH
• Trichomes * growth & development   genetics   metabolism   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Metals * MeSH
• Arabidopsis Proteins MeSH

Formins are a large, evolutionarily old family of cytoskeletal regulators whose roles include actin capping and nucleation, as well as modulation of microtubule dynamics. The plant class I formin clade is characterized by a unique domain organization, as most of its members are transmembrane proteins with possible cell wall-binding motifs exposed to the extracytoplasmic space-a structure that appears to be a synapomorphy of the plant kingdom. While such transmembrane formins are traditionally considered mainly as plasmalemma-localized proteins contributing to the organization of the cell cortex, we review, from a cell biology perspective, the growing evidence that they can also, at least temporarily, reside (and in some cases also function) in endomembranes including secretory and endocytotic pathway compartments, the endoplasmic reticulum, the nuclear envelope, and the tonoplast. Based on this evidence, we propose that class I formins may thus serve as 'active cargoes' of membrane trafficking-membrane-embedded proteins that modulate the fate of endo- or exocytotic compartments while being transported by them.

• Keywords
• Actin, biotic interactions, cell growth, cytokinesis, endocytosis, exocytosis, formin, microtubules, plasmalemma, tonoplast,
• MeSH
• Cell Membrane * metabolism   MeSH
• Formins * metabolism   MeSH
• Membrane Proteins metabolism   genetics   MeSH
• Plant Proteins metabolism   genetics   MeSH
• Protein Transport * MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Formins * MeSH
• Membrane Proteins MeSH
• Plant Proteins MeSH

Protein complex Arp2/3 has a conserved role in the nucleation of branched actin filaments. It is constituted of seven subunits, including actin-like subunits ARP2 and ARP3 plus five other subunits called Arp2/3 Complex Component 1 to 5, which are not related to actin. Knock-out plant mutants lacking individual plant ARP2/3 subunits have a typical phenotype of distorted trichomes, altered pavement cells shape and defects in cell adhesion. While knock-out mutant Arabidopsis plants for most ARP2/3 subunits have been characterized before, Arabidopsis plant mutants missing ARPC1 and ARPC3 subunits have not yet been described. Using CRISPR/Cas9, we generated knock-out mutants lacking ARPC1 and ARPC3 subunits. We confirmed that the loss of ARPC1 subunits results in the typical ARP2/3 mutant phenotype. However, the mutants lacking ARPC3 subunits resulted in plants with surprisingly different phenotypes. Our results suggest that plant ARP2/3 complex function in trichome shaping does not require ARPC3 subunit, while the fully assembled complex is necessary for the establishment of correct cell adhesion in the epidermis.

• MeSH
• Actins metabolism   MeSH
• Arabidopsis * genetics   metabolism   MeSH
• CRISPR-Cas Systems MeSH
• Actin-Related Protein 2-3 Complex * genetics   metabolism   MeSH
• Actin-Related Protein 2 genetics   MeSH
• Actin-Related Protein 3 metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Actins MeSH
• Actin-Related Protein 2-3 Complex * MeSH
• Actin-Related Protein 2 MeSH
• Actin-Related Protein 3 MeSH

Primary root growth is required by the plant to anchor in the soil and reach out for nutrients and water, while dealing with obstacles. Efficient root elongation and bending depends upon the coordinated action of environmental sensing, signal transduction, and growth responses. The actin cytoskeleton is a highly plastic network that constitutes a point of integration for environmental stimuli and hormonal pathways. In this review, we present a detailed compilation highlighting the importance of the actin cytoskeleton during primary root growth and we describe how actin-binding proteins, plant hormones, and actin-disrupting drugs affect root growth and root actin. We also discuss the feedback loop between actin and root responses to light and gravity. Actin affects cell division and elongation through the control of its own organization. We remark upon the importance of longitudinally oriented actin bundles as a hallmark of cell elongation as well as the role of the actin cytoskeleton in protein trafficking and vacuolar reshaping during this process. The actin network is shaped by a plethora of actin-binding proteins; however, there is still a large gap in connecting the molecular function of these proteins with their developmental effects. Here, we summarize their function and known effects on primary root growth with a focus on their high level of specialization. Light and gravity are key factors that help us understand root growth directionality. The response of the root to gravity relies on hormonal, particularly auxin, homeostasis, and the actin cytoskeleton. Actin is necessary for the perception of the gravity stimulus via the repositioning of sedimenting statoliths, but it is also involved in mediating the growth response via the trafficking of auxin transporters and cell elongation. Furthermore, auxin and auxin analogs can affect the composition of the actin network, indicating a potential feedback loop. Light, in its turn, affects actin organization and hence, root growth, although its precise role remains largely unknown. Recently, fundamental studies with the latest techniques have given us more in-depth knowledge of the role and organization of actin in the coordination of root growth; however, there remains a lot to discover, especially in how actin organization helps cell shaping, and therefore root growth.

• Keywords
• actin, actin-binding protein, auxin, cell elongation, gravitropism, light, root growth,
• Publication type
• Journal Article MeSH
• Review MeSH