Plant signaling is fundamental for survival under a changing environment. Many signaling pathways require scaffold proteins which form complexes with ligands in proximity to trigger effectors that activate or inhibit appropriate response cascades. The so-called WD-repeat (WDR) proteins comprise an astonishingly diverse superfamily of regulatory proteins, representing the breadth of biochemical mechanisms and cellular processes. These proteins have been found to play key roles in such disparate mechanisms as signal transduction, cytoskeletal dynamics, protein trafficking, nuclear export and RNA processing, and are especially prevalent in chromatin modification and transcriptional mechanisms. WDR proteins are intimately involved in a variety of cellular and organismal processes, including cell division and cytokinesis, apoptosis, light signaling and vision, cell motility, flowering, floral development, and meristem organization, to name a few. Within the cell, WDR proteins have been found to be components of the cytoplasm or nucleoplasm, linked to the cytoskeleton, or associated with membranes through binding to membrane proteins or through membrane-interacting, ancillary domains. Known WDR proteins range in size from small proteins such as the pleiotropic plant developmental regulator VIP3 (34 kDa), to massive (> 400-kDa) proteins such as the mammalian protein trafficking factor Lyst. In addition, WDR proteins include those containing a conserved core of approximately 40 amino acids which usually end with a tryptophan-aspartic acid dipeptide (WD40). They belong to a large and fast-expanding conservative protein family in which this conserved domain is usually found in sets of seven to eight WD40 repeats capable of self-assembly into blade-shape platforms of a typical structure called the ß-propeller. These proteins are often conformed into such seven-blade structure in either monomeric or dimeric form. This conformation permits specific protein-protein interactions leading to complex formation and relocalization to target sites for appropriate responses to stimuli. For example, the six-bladed Sec13 is a component of the Coat protein II (COP II) coat and the nuclear pore complex (NPC), and is involved in vesicle biogenesis; the seven-bladed ß-subunit of the heterotrimeric G protein is involved in multiple signaling pathways mediated by G-protein coupled receptors; and the seven-bladed dimeric Actin-interacting protein I (AIP) binds to the F-actin-cofilin complex and enhances actin filament disassembly in the presence of actin-depolymerizing factor (ADF). Hence, WD40 domain proteins have varied interacting partners and are involved in as diverse functions as cell motility, division and cytokinesis, apoptosis, light signaling and vision, environmental stress, flowering and floral development, and meristem organization, to mention a few. Thus, WDR proteins are essential components of most eukaryotic functions and survival responses to their environment. While most information on WDR protein function comes from animal cell studies, recent discoveries on WDR protein homologs and their functional analyses from plants have shed some light on how many signaling cascades are regulated and how vast the interactive components are within these pathways. This Research Topic will include new discoveries and critical reviews on the actual state of the field of this unique protein family.
Plant signaling is fundamental for survival under a changing environment. Many signaling pathways require scaffold proteins which form complexes with ligands in proximity to trigger effectors that activate or inhibit appropriate response cascades. The so-called WD-repeat (WDR) proteins comprise an astonishingly diverse superfamily of regulatory proteins, representing the breadth of biochemical mechanisms and cellular processes. These proteins have been found to play key roles in such disparate mechanisms as signal transduction, cytoskeletal dynamics, protein trafficking, nuclear export and RNA processing, and are especially prevalent in chromatin modification and transcriptional mechanisms. WDR proteins are intimately involved in a variety of cellular and organismal processes, including cell division and cytokinesis, apoptosis, light signaling and vision, cell motility, flowering, floral development, and meristem organization, to name a few. Within the cell, WDR proteins have been found to be components of the cytoplasm or nucleoplasm, linked to the cytoskeleton, or associated with membranes through binding to membrane proteins or through membrane-interacting, ancillary domains. Known WDR proteins range in size from small proteins such as the pleiotropic plant developmental regulator VIP3 (34 kDa), to massive (> 400-kDa) proteins such as the mammalian protein trafficking factor Lyst. In addition, WDR proteins include those containing a conserved core of approximately 40 amino acids which usually end with a tryptophan-aspartic acid dipeptide (WD40). They belong to a large and fast-expanding conservative protein family in which this conserved domain is usually found in sets of seven to eight WD40 repeats capable of self-assembly into blade-shape platforms of a typical structure called the ß-propeller. These proteins are often conformed into such seven-blade structure in either monomeric or dimeric form. This conformation permits specific protein-protein interactions leading to complex formation and relocalization to target sites for appropriate responses to stimuli. For example, the six-bladed Sec13 is a component of the Coat protein II (COP II) coat and the nuclear pore complex (NPC), and is involved in vesicle biogenesis; the seven-bladed ß-subunit of the heterotrimeric G protein is involved in multiple signaling pathways mediated by G-protein coupled receptors; and the seven-bladed dimeric Actin-interacting protein I (AIP) binds to the F-actin-cofilin complex and enhances actin filament disassembly in the presence of actin-depolymerizing factor (ADF). Hence, WD40 domain proteins have varied interacting partners and are involved in as diverse functions as cell motility, division and cytokinesis, apoptosis, light signaling and vision, environmental stress, flowering and floral development, and meristem organization, to mention a few. Thus, WDR proteins are essential components of most eukaryotic functions and survival responses to their environment. While most information on WDR protein function comes from animal cell studies, recent discoveries on WDR protein homologs and their functional analyses from plants have shed some light on how many signaling cascades are regulated and how vast the interactive components are within these pathways. This Research Topic will include new discoveries and critical reviews on the actual state of the field of this unique protein family.
