Abstract
Prenylation primarily by geranylgeranylation is required for membrane attachment and function of type I Rho of Plants (ROPs) and Gγ proteins, while type II ROPs are attached to the plasma membrane by S-acylation. Yet, it is not known how prenylation affects ROP membrane interaction dynamics and what are the functional redundancy and specificity of type I and type II ROPs. Here, we have used the expression of ROPs in mammalian cells together with geranylgeranylation and CaaX prenylation-deficient mutants to answer these questions. Our results show that the mechanism of type II ROP S-acylation and membrane attachment is unique to plants and likely responsible for the viability of plants in the absence of CaaX prenylation activity. The prenylation of ROPs determines their steady-state distribution between the plasma membrane and the cytosol but has little effect on membrane interaction dynamics. In addition, the prenyl group type has only minor effects on ROP function. Phenotypic analysis of the CaaX prenylation-deficient pluripetala mutant epidermal cells revealed that type I ROPs affect cell structure primarily on the adaxial side, while type II ROPs are functional and induce a novel cell division phenotype in this genetic background. Taken together, our studies show how prenyl and S-acyl lipid modifications affect ROP subcellular distribution, membrane interaction dynamics, and function.
Highlights
Prenylation primarily by geranylgeranylation is required for membrane attachment and function of type I Rho of Plants (ROPs) and Gg proteins, while type II ROPs are attached to the plasma membrane by S-acylation
GFP-rop6CA was associated with lamellipodia enriched with phaloidine-labeled actin (Fig. 1, E–G, arrowheads in G)
Since the G-domains of type I and type II ROPs are highly similar (Berken and Wittinghofer, 2008), the functionality of ROP6 compared with ROP9 in the mammalian cells likely resulted from their ability to interact with the plasma membrane
Summary
Prenylation primarily by geranylgeranylation is required for membrane attachment and function of type I Rho of Plants (ROPs) and Gg proteins, while type II ROPs are attached to the plasma membrane by S-acylation. Corresponding to the mild phenotype of pggt-Ib, only a minor mislocalization of the Gg-subunit AGG1 was observed in the pggt-Ib background, while plp mutant plants showed accumulation of AGG1 in the soluble fraction (Zeng et al, 2007). Taken together, these data suggested that in Arabidopsis, PFT function could almost fully compensate for the loss of PGGT-I. Whereas type I ROPs terminate with a canonical prenylation CaaL box motif and are prenylated by PGGT-I, type II ROPs do not have a functional CaaX box prenylation motif and instead contain a plant-specific motif called the GC-
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