Protein Prenylation Makeovers in Plants: Insights into Substrate Diversification.

Type-I protein prenylation, the post-translational modification of CaaX motif-containing proteins, relies on two substrates: the target protein and a mevalonate-derived prenyl diphosphate co-substrate, either farnesyl diphosphate (FPP) or geranylgeranyl diphosphate (GGPP). Two enzymes, protein farnesyltransferase and type-I geranylgeranyltransferase, recognize and bind both co-substrates. Modifying potentially hundreds of distinct protein targets within a constrained timeframe poses a major regulatory challenge for the cell. However, the mechanisms controlling prenyltransferase activity, including substrate availability, enzyme specificity, and catalytic efficiency, remain poorly understood, particularly in plants. Plant prenylation systems exhibit distinctive features. The diversity of prenyl diphosphate donors is expanded by the plastidial methylerythritol phosphate pathway, which supplements the mevalonate pathway and may provide alternative prenyl groups beyond the canonical FPP and GGPP. Additionally, many CaaX-containing proteins are plant-specific, and post-transcriptional modifications generate multiple prenylatable isoforms, increasing substrate complexity. In this review, we examine the diversification of both prenyl diphosphate donors and protein substrates in plants, hypothesizing that such diversification may illuminate key mechanisms underlying the cellular regulation of protein prenylation.