Intrinsically disordered proteins (IDPs) are a group of functional proteins without defined
3D structures. Some structured proteins contain ordered domains and functional intrinsically
disordered regions (IDRs). Rather than having a single fixed structure, IDPs/IDRs may adopt
various conformations depending on different situations ...
Intrinsically disordered proteins (IDPs) are a group of functional proteins without defined
3D structures. Some structured proteins contain ordered domains and functional intrinsically
disordered regions (IDRs). Rather than having a single fixed structure, IDPs/IDRs may adopt
various conformations depending on different situations (Kim and Han, 2018; Uversky, 2019).
Because of the structural flexibility, IDPs/IDRs are not restricted to lock-key modules but rather
interact with different partners under different circumstances. Thus, IDPs/IDRs have versatile roles
and multiple functions in numerous biological processes (Tompa et al., 2015; Uversky, 2019).
IDRs of transcription factors are proposed to provide functional versatility in molecular
recognition via their binding plasticity, which facilitates transcriptional regulation of structural
domains (Sun et al., 2012). IDPs/IDRs are key factors triggering liquid–liquid phase
separation/transition (LLPS/LLPT), which forms membrane-less compartments apart from liquid
fluid in a cell, also known as biomolecular condensates, thus allowing the spatiotemporal
organization of biochemical reactions by concentrating macromolecules locally (Cuevas-Velazquez
and Dinneny, 2018; Kim et al., 2021). In plants, IDRs of transcription factors and signal
transduction proteins often form flexible interaction networks or receive various signals, such
as plant-specific NAC (for NO APICAL MERISTEM, ATAF, CUP-SHAPED COTYLEDON)
transcription factors involved in seed germination and seedling establishment and GRAS (for
GIBBERELLIC ACID INSENSITIVE, REPRESSOR of GAI, and the SCARECROW) proteins
functioning in gibberellic acid signaling, whereas specific classes of IDPs are involved in flowering
and abiotic stress responses (Sun et al., 2013; Covarrubias et al., 2017). Typical examples of
plant IDRs/IDPs are shown in Figure 1A. Readers are invited to visit the previous review papers
regarding specific topics such as plant IDPs (Sun et al., 2013; Covarrubias et al., 2017), LLPS in
plants (Cuevas-Velazquez and Dinneny, 2018; Kim et al., 2021), and dehydrins in stress responses
(Cuevas-Velazquez et al., 2014; Graether and Boddington, 2014; Kosová et al., 2014; Yu et al., 2018).
Instead of summarizing the versatile functions of IDPs/IDRs in detail as in the aforementioned
review papers, this article highlights the recent breakthroughs in plant IDP/IDR research to
provide the whole-picture view; proposes conceptual principles of their action modes on spatial
regulation, broad specificity, and signaling/physiological switch; and calls for more research in this
emerging field.
