A RHOse by any other name: a comparative analysis of animal and plant Rho GTPases

Abstract

Rho GTPases are molecular switches that act as key regulators of a many cellular processes, including cell movement, morphogenesis, host defense, cell division and gene expression. Rho GTPases are found in all eukaryotic kingdoms. Plants lack clear homologs to conventional Rho GTPases found in yeast and animals; instead, they have over time developed a unique subfamily, ROPs, also known as RAC. The origin of ROP-like proteins appears to precede the appearance of land plants. This review aims to discuss the evolution of ROP/RAC and to compare plant ROP and animal Rho GTPases, focusing on similarities and differences in regulation of the GTPases and their downstream effectors.

An actin cytoskeleton with evolutionarily conserved functions in the absence of canonical actin-binding proteins

“…3B). Consistent with Giardia being an early diverging eukaryote, its genome contains a single Rac homolog (28) and Rac is thought to be the founding member of the Rho family of small G proteins (29). To test for a conserved actin-signaling response in Giardia, we constructed a constitutive active Q74L giRac (equivalent to Q61L Rac1) (30).…”

Signals fly when kinases meet Rho-of-plants (ROP) small G-proteins

“…Only one of the RopGAPs bears MAPK 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 phosphorylation signatures [80]. This RopGAP (gene code At5g61530), which has a strong pollen-specific expression, is the sole member of an Arabidopsis RopGAP family with no other domains but the catalytic domain [3]. After the in vitro verification of phosphorylation, the expression of phosphomimetic or non-phosphorylatable mutant versions of the protein in pollen tubes could give an indication of the existence and biological significance of this potential regulatory step.…”

“…ROPs to receive and transmit signals are conserved among yeasts, animals, and plants, whereas others are specific [3] (Table 1).…”

“…1). The GTP-bearing Rho G-proteins perform their regulatory function through a conformation-specific interaction with target (effector) proteins 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 subfamilies of other eukaryotes [2,3] (Table 1). The Rop subfamily is represented by 14 proteins in Arabidopsis and by seven in rice [5].…”

“…ROPs share only a few downstream effectors with other eukaryotes (Table 1), such as the plasma membrane NADPH oxidase and certain actin nucleation complexes [3]. ROPs have several plant-specific effectors, including enzymes that play a role in cell wall synthesis, and plant-specific small scaffold proteins [2 4].…”