An ancient RAB5 governs the formation of additional vacuoles and cell shape in petunia petals

Global organization of phenylpropanoid and anthocyanin pathways revealed by proximity labeling of trans-cinnamic acid 4-hydroxylase in Petunia inflata petal protoplasts

The phenylpropanoid pathway is one of the main carbon sinks in plants, channeling phenylalanine towards thousands of products including monolignols, stilbenes, flavonoids and volatile compounds. The enzymatic steps involved in many of these pathways are well characterized, however the physical organization of these enzymes within the plant cell remains poorly understood. Proximity-dependent labeling allows untargeted determination of both direct and indirect protein interactions in vivo, and therefore stands as an attractive alternative to targeted binary assays for determining global protein-protein interaction networks. We used TurboID-based proximity labeling to study protein interaction networks of the core phenylpropanoid and anthocyanin pathways in petunia. To do so, we coupled the endoplasmic reticulum (ER) membrane anchored cytochrome P450 cinnamic acid 4-hydroxylase (C4H, CYP73A412) from Petunia inflata to TurboID and expressed it in protoplasts derived from anthocyanin-rich petunia petals. We identified multiple soluble enzymes from the late anthocyanin pathway among enriched proteins, along with other C4H isoforms, and other ER membrane anchored CYPs. Several of these interactions were subsequently confirmed by bimolecular fluorescence complementation (BiFC). Our results suggest that C4H co-localizes with enzymes from the phenylpropanoid- and downstream anthocyanin pathways, supporting the idea that C4H may serve as ER anchoring points for downstream metabolic pathways. Moreover, this study demonstrates the feasibility of using protoplasts to perform global mapping of protein network for enzymes in their native cellular environment.

Analysis of Plant-Specific ANTH Domain-Containing Protein in Marchantia polymorpha

Membrane trafficking is a fundamental mechanism for protein and lipid transport in eukaryotic cells and exhibits marked diversity among eukaryotic lineages with distinctive body plans and lifestyles. Diversification of the membrane trafficking system is associated with the expansion and secondary loss of key machinery components, including RAB GTPases, soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) and adaptor proteins, during plant evolution. The number of AP180 N-terminal homology (ANTH) proteins, an adaptor family that regulates vesicle formation and cargo sorting during clathrin-mediated endocytosis, increases during plant evolution. In the genome of Arabidopsis thaliana, 18 genes for ANTH proteins have been identified, a higher number than that in yeast and animals, suggesting a distinctive diversification of ANTH proteins. Conversely, the liverwort Marchantia polymorpha possesses a simpler repertoire; only two genes encoding canonical ANTH proteins have been identified in its genome. Intriguingly, a non-canonical ANTH protein is encoded in the genome of M. polymorpha, which also harbors a putative kinase domain. Similar proteins have been detected in sporadic lineages of plants, suggesting their ancient origin and multiple secondary losses during evolution. We named this unique ANTH group phosphatidylinositol-binding clathrin assembly protein-K (PICALM-K) and characterized it in M. polymorpha using genetic, cell biology-based and artificial intelligence (AI)-based approaches. Our results indicate a flagella-related function of MpPICALM-K in spermatozoids, which is distinct from that of canonical ANTH proteins. Therefore, ANTH proteins have undergone significant functional diversification during evolution, and PICALM-K represents a plant-unique ANTH protein that is delivered by neofunctionalization through exon shuffling.

The Amsterdam petunia germplasm collection: A tool in plant science

Petunia hybrida is a plant model system used by many researchers to investigate a broad range of biological questions. One of the reasons for the success of this organism as a lab model is the existence of numerous mutants, involved in a wide range of processes, and the ever-increasing size of this collection owing to a highly active and efficient transposon system. We report here on the origin of petunia-based research and describe the collection of petunia lines housed in the University of Amsterdam, where many of the existing genotypes are maintained.

A Role for Two-Pore Channel Type 2 (TPC2)-Mediated Regulation of Membrane Contact Sites During Zebrafish Notochord Biogenesis?

We have previously shown that in the developing trunk of zebrafish embryos, two-pore channel type 2 (TPC2)-mediated Ca2+ release from endolysosomes plays a role in the formation of the skeletal slow muscle. In addition, TPC2-mediated Ca2+ signaling is required for axon extension and the establishment of synchronized activity in the primary motor neurons. Here, we report that TPC2 might also play a role in the development of the notochord of zebrafish embryos. For example, when tpcn2 was knocked down or out, increased numbers of small vacuoles were formed in the inner notochord cells, compared with the single large vacuole in the notochord of control embryos. This abnormal vacuolation was associated with embryos displaying attenuated body axis straightening. We also showed that TPC2 has a distinct pattern of localization in the notochord in embryos at ∼24 hpf. Finally, we conducted RNAseq to identify differentially expressed genes in tpcn2 mutants compared to wild-type controls, and found that those involved in actin filament severing, cellular component morphogenesis, Ca2+ binding, and structural constituent of cytoskeleton were downregulated in the mutants. Together, our data suggest that TPC2 activity plays a key role in notochord biogenesis in zebrafish embryos.