PROSITE documentation PDOC52095

FANTASTIC FOUR (FAF) domain profile

Plant development and environmental adaptation are governed by complex regulatory networks, in which small, plant-specific proteins often function as modulatory components. The FANTASTIC FOUR (FAF) protein family represents one such group of regulatory proteins. FAF proteins, despite their simple structure, are crucial regulators of developmental processes. FAF genes were first identified in Arabidopsis thaliana and encode small proteins that are highly conserved across land plants and share a FAF domain of ~50 amino acids. Since their initial identification in Arabidopsis thaliana, FAF domain-containing proteins have been linked to shoot apical meristem maintenance, organ initiation, and developmental timing, positioning them as modulators that fine-tune growth-related signaling pathways. FAF domain-containing proteins act as context-dependent modulators whose roles depend on tissue type and developmental status. The observed cytoplasmic localization and lack of recognizable DNA-binding domains and transcriptional activation motifs suggest that FAF domain-containg proteins are unlikely to function as classical transcription factors and may instead act as modulatory components within protein complexes. FAF domain-containing proteins may act as modulators of key developmental hubs [1].

The FAF domain is made of two two-stranded antiparallel β-sheets spreading apart. A short α-helix is located in between the two two-stranded antiparallel β-sheets [1,2].

Some proteins known to contain a FAF domain are listed below:

• Arabidopsis thaliana FAF1, FAF2, FAF3 and FAF4, that influence shoot meristem size [3].
• Arabidopsis thaliana FAF-like, a more distantly related protein which shares several conserved domains [3].
• Tomato FAF1/2a, FAF1/2b, FAF1/2c, FAF3/4a and FAF3/4b, homologues of Arabidopsis FAFs which positively or negatively regulate flowering time [4].
• Tomato Cell Size Regulator (CSR), mainly expressed in fruit tissues and vascular bundles during the fruit maturation process, which ultimately lead to increases in the mesocarp cell size and fruit weight [4,5].
• Tomato CSR-like 1 to 3 [5].
• Maize Enhancer of ABA Co-Receptor1 (EAR1) protein, a negative regulator of abscisic acid (ABA) signaling that interacts with the inhibition domain at the N termini of type 2C protein phosphatases (PP2Cs) [6].
• Maize sugary enhancer1 (se1), a protein affecting endosperm starch metabolism [7].
• Rice Vegetative Cell Specific 1 (VCS1), might function in the tapetum and influence the generation of microspores [8].
• Wheat TaFAF-5D.5 protein, associated with both developmental adaptation and heat stress responses [1].

The profile we developed covers the entire FAF domain.