A molecular basis for plant SCAR/WAVE functional divergence

Dynamic actin cytoskeleton reorganisation enables plant developmental processes requiring polarised transport such as root hair and leaf trichome formation. The SCAR/WAVE complex plays a crucial role in regulating these dynamics through ARP2/3-mediated actin branching. SCAR/WAVE genes occur as small families across a wide range of plant species but whether and how they fulfil different functions remains unclear. We utilise a systematic chimaera approach to define the differential functionality of two closely related Medicago truncatula SCAR proteins in plant development. We show that SCAR/WAVE contribution to Medicago truncatula root hair or Arabidopsis thaliana trichome formation is dependent on two central intrinsically disordered regions (IDRs). Differential functionalities of Medicago truncatula SCAR proteins were furthermore associated with the presence/absence of a 42-amino acid sequence within the IDR that impacted protein stability. Through uncovering a molecular basis for functional differences, we advance our understanding of plant SCAR/WAVE complexes. One Sentence SummaryIntrinsically disordered regions in SCAR/WAVE proteins drive diverse functions in root hair and leaf trichome development.