Rab‐E and its interaction with myosin XI are essential for polarised cell growth

Abstract

The fundamental process of polarised exocytosis requires the interconnected activity of molecular motors trafficking vesicular cargo within a dynamic cytoskeletal network. In plants, few mechanistic details are known about how molecular motors, such as myosin XI, associate with their secretory cargo to support the ubiquitous processes of polarised growth and cell division. Live-cell imaging coupled with targeted gene knockouts and a high-throughput RNAi assay enabled the first characterisation of the loss of Rab-E function. Yeast two-hybrid and subsequent in silico structural prediction uncovered a specific interaction between Rab-E and myosin XI that is conserved between P. patens and A. thaliana. Rab-E co-localises with myosin XI at sites of active exocytosis, and at the growing tip both proteins are spatiotemporally coupled. Rab-E is required for normal plant growth in P. patens and the rab-E and myosin XI phenotypes are rescued by A. thaliana's Rab-E1c and myosin XI-K/E, respectively. Both PpMyoXI and AtMyoXI-K interact with PpRabE14, and the interaction is specifically mediated by PpMyoXI residue V1422. This interaction is required for polarised growth. Our results suggest that the interaction of Rab-E and myosin XI is a conserved feature of polarised growth in plants.

Structure of the class XI myosin globular tail reveals evolutionary hallmarks for cargo recognition in plants

“…Sequence comparisons show that this site is also divergent in other MyoXI subclasses, indicating that the molecular determinants for the binding of Rab-like proteins in plant MyoXIs cannot be explained by the data available for Rab11-MyoV complexes. The Rab-binding region may even be the same, as suggested by a study of the MyoXI-A-RabE interaction (Orr et al, 2021), but structural studies on plant-relevant complexes are required to unravel the molecular determinants for this recognition. Even among MyoVs, it is difficult to accurately predict which Rabs can interact with a given binding site.…”

“…In contrast, human MyoVa and MyoVb bind to Rab11, like Myo2p, but seem to recognize Rab8 using a domain upstream of the GTD (Pashkova et al, 2006;Pylypenko et al, 2013Pylypenko et al, , 2016Roland et al, 2011;Lindsay et al, 2013). In plants, the known interactions between MyoXIs and Rabs are as yet limited to the RabC (Rab18), RabD (Rab1) and RabE (Rab8) subfamilies (Hashimoto et al, 2008;Orr et al, 2021) and require further structural studies to elucidate their molecular basis. Intriguingly, the molecular motor linking RabA (Rab11) to the actin cytoskeleton in plants has not yet been found, and is an interesting question to be addressed in future work.…”

“…In plants, it was observed that the GTD of Physcomitrella patens MyoXI-A, which is 72% identical to AtMyoXI-K, interacts with RabE, a homolog of yeast Sec4, by an as yet elusive interaction mechanism (Orr et al, 2021). Furthermore, the A. thaliana genome encodes a homolog of human Rab11A, named AtRab11C (NP_172434.1).…”

“…(c) Structure superimposition between MyoXI-K and the MyoVa-Rab11A complex (PDB entry 5jcz;Pylypenko et al, 2016), showing the steric clash between the side chain of the His1416 residue of MyoXI-K and the surface of Rab11A, and the elongated 7 in MyoXI-K, which prevents the 6-7 loop from contacting Rab11A. The star indicates the residue equivalent to Val1422 from moss myosin XI-A, which seems to play a role in RabE recognition(Orr et al, 2021).…”

Funkcje białek Rab w roślinach – na poziomie komórki i organizmu

“…Na przykład białka RabE w Arabidopsis modyfikują skład lipidów w otaczającej je błonie, co prowadzi do rozgałęziania się włośników korzeniowych [21,22]. U mchu Physcomitrella patens białko RabE oddziałuje z miozyną IX i bierze udział we wzroście wierzchołkowym komórek gametofitu [23]. Mutacje w genie kodującym białko LOT (ang.…”