siRNA screening of Rab GTPases reveal a role of Rab3b and Rab3c positive vesicles in cross presentation

Antigen cross-presentation in dendritic cells is a complex intracellular membrane transport process, but the underlying molecular mechanisms remain to be thoroughly investigated.

Regulation of Neutral Lipid Retention by Rab GTPases and Mono-ADP-Ribosylation of CtBP1/BARS

Aberration of lipid storage in lipid droplets (LD) has been linked with the development and progression of several common metabolic diseases including obesity, type II diabetes,

FgRab5 and FgRab7 are essential for endosomes biogenesis and nonredundantly recruit the retromer complex to the endosomes in Fusarium graminearum

The retromer complex,composed of the cargo-selective complex(CSC)Vps35-Vps29-Vps26 in complex with the sorting nexin dimer Vps5-Vps17,mediates the sorting and retrograde transport of cargo proteins from the endosomes to the trans-Golgi network in eukaryotic cells.Rab proteins belong to the Ras superfamily of small GTPases and regulate many trafficking events including vesicle formation,budding,transport,tethering,docking and fusion with target membranes.Herein,we investigated the potential functional relationship between the retromer complex and the 11 Rab proteins that exist in Fusarium graminearum using genetic and high-resolution laser confocal microscopic approaches.We found that only FgRab5(FgRab5A and FgRab5B)and FgRab7 associate with the retromer complex.Both FgVps35-GFP and FgVps17-GFP are mis-localized and appear diffused in the cytoplasm ofΔFgrab5A,ΔFgrab5B andΔFgrab7 mutants as compared to their punctate localization within the endosomes of the wild-type.FgRab7 and FgRab5B were found to co-localize with the retromer on endosomal membranes.Most strikingly,we found that these three Rab GTPases are indispensable for endosome biogenesis as both early and late endosomes could not be detected in the cells of the mutants after FM4-64 staining of the cells,while they were very clearly seen in the wild-type PH-1.Furthermore,FgRab7 was found to recruit FgVps35 but not FgVps17 to the endosomal membranes,whereas FgRab5B recruits both FgVps35 and FgVps17 to the membranes.Thus,we conclude that the Rab proteins FgRab5A,FgRab5B and FgRab7 play critical roles in the biogenesis of endosomes and in regulating retromer-mediated trafficking in F.graminearum.

Complementation and Expression Analysis of SoRablA and SoRab2A in Sugarcane Demonstrates Their Functional Diversification

Mammalian and plant Rabl and Rab2 are small GTPases that regulate vesicle trafficking in the endoplasmic reticulum （ER） to Golgi compartments. Little is known about their functional diversification or potential interaction. We cloned sugarcane （Saccharum officinarum L.） Rab1A and Rab2A genes and studied their functional differences by expression and complementation experiments. We found differential expression of the two genes during sugarcane leaf development： SoRab2A expression declined from the dividing base to the maturing tip of the growing leaves, whereas SoRab1A was constitutively expressed, suggesting that SoRab2A is required for cell division and expansion and SoRablA is required for cells at all developmental stages. We used a yeast temperature sensitive ypt1-A 136D mutant strain to further investigate these shared and unique functions. Yptl is a small GTPase that regulates vesicle transport in the same cellular location as Rabl and Rab2. Neither SoRab1A nor SoRab2A alone could restore the growth of the mutant at restrictive temperatures when SoRab1A and SoRab2A were transformed separately. However, SoRab1A transformants maintained normal morphology and viability at non-permissive temperature, and resumed growth when returned to permissive temperature, whereas SoRab2A transformants died at non-permissive temperature, suggesting that SoRablA function is required for a cell＇s viability. Mutant growth was fully restored when SoRab1A and SoRab2A were co-transformed, indicating that SoRablA and SoRab2A complement each other and they both are needed to restore the function of ypt1-A136D. These results demonstrate that SoRab1A and SoRab2A serve distinct but overlapping functions, mostly by regulating the transportation of different sets of proteins.

Actin-depolymerizing factors 8 and 11 promote root hair elongation at high pH

A root hair is a polarly elongated single-celled structure that derives from a root epidermal cell and func-tions in uptake of water and nutrients from the surrounding environment.Previous reports have demon-strated that short periods of high pH inhibit root hair extension;but the effects of long-term high-pH treat-ment on root hair growth are still unclear.Here,we report that the duration of root hair elongation is signicantly prolonged with increasing external pH,which counteracts the effect of decreasing root hair elongation rate and ultimately produces longer root hairs,whereas loss of actin-depolymerizing factor 8 and 11(ADF8/11)function causes shortening of root hair length at high pH(pH 7.4).Accumulation of ADF8/11 at the tips of root hairs is inhibited by high pH,and increasing environmental pH affects the actinlament(F-actin)meshwork at the root hair tip.At high pH,the tip-focused F-actin meshwork is absent in root hairs of the adf8/11 mutant,actinlaments are disordered at the adf8/11 root hair tips,and actin turn-over is attenuated.Secretory and recycling vesicles do not aggregate in the apical region of adf8/11 root hairs at high pH.Together,our results suggest that,under long-term exposure to high extracellular pH,ADF8/11 may establish and maintain the tip-focused F-actin meshwork to regulate polar trafcking of secretory/recycling vesicles at the root hair tips,thereby promoting root hair elongation.

Biogenesis of Plant Prevacuolar Multivesicular Bodies

Plant prevacuolar compartments （PVCs）, or multivesicular bodies （MVBs）, are single membrane-bound organelles that play important roles in mediating protein trafficking to vacuoles in the secretory pathway. PVC/MVB also serves as a late endosome in the endocytic pathway in plants. Since the plant PVC was iden- tified as an MVB more than 10 years ago,-great progress has been made toward the understanding of PVC/ MVB function and biogenesis in plants. In this review, we first summarize previous research into the iden- tification and characterization of plant PVCs/MVBs, and then highlight recent advances on the mechanisms underlying intraluminal vesicle formation and maturation of plant PVCs/MVBs. In addition, we discuss the possible crosstalk that appears to occur between PVCs/MVBs and autophagosomes during autophagy in plants. Finally, we list some open questions and present future perspectives in this field.

The biogenesis and secretion of exosomes and multivesicular bodies(MVBs):Intercellular shuttles and implications in human diseases

Exosomes carry and transmit signaling molecules used for intercellular communication.The generation and secretion of exosomes is a multistep interlocking process that allows simultaneous control of multiple regulatory sites.Protein molecules,mainly RAB GTPases,cytoskeletal proteins and soluble N-ethylmaleimide-sensitive fusion attachment protein receptor(SNARE),are specifically regulated in response to pathological conditions such as altered cellular microenvironment,stimulation by pathogenic factors,or gene mutation.This interferes with the smooth functioning of endocytosis,translocation,degradation,docking and fusion processes,leading to changes in the secretion of exosomes.Large numbers of secreted exosomes are disseminated by the flow of body fluids and absorbed by the recipient cells.By transmitting characteristic functional proteins and genetic information produced under disease conditions,exosomes can change the physiological state of the recipient cells and their microenvironment.The microenvironment,in turn,affects the occurrence and development of disease.Therefore,this review will discuss the mechanism by which exosome secretion is regulated in cells following the formation of mature secretory multivesicular bodies(MVBs).The overall aim is to find ways to eliminate disease-derived exosomes at their source,thereby providing an important new basis for the clinical treatment of disease.