Rhodopsin has been used as a prototype system to investigate G protein-coupled receptor (GPCR) internalization and endocytic sorting mechanisms. Failure of rhodopsin recycling upon light activation results in various degenerative retinal diseases. Accumulation of internalized rhodopsin in late endosomes and the impairment of its lysosomal degradation are associated with unregulated cell death that occurs in dystrophies. However, the molecular basis of rhodopsin accumulation remains elusive. We found that the novel norpAP24 suppressor, diehard4, is responsible for the inability of endo-lysosomal rhodopsin trafficking and retinal degeneration in Drosophila models of retinal dystrophies. We found that diehard4 encodes Osiris 21. Loss of its function suppresses retinal degeneration in norpAP24, rdgC306, and trp1, but not in rdgB2, suggesting a common cause of photoreceptor death. In addition, the loss of Osiris 21 function shifts the membrane balance between late endosomes and lysosomes as evidenced by smaller late endosomes and the proliferation of lysosomal compartments, thus facilitating the degradation of endocytosed rhodopsin. Our results demonstrate the existence of negative regulation in vesicular traffic between endosomes and lysosomes. We anticipate that the identification of additional components and an in-depth description of this specific molecular machinery will aid in therapeutic interventions of various retinal dystrophies and GPCR-related human diseases.

Photoreceptors are light-sensitive proteins found in various organisms that respond to light and relay signals into the cells. Heliorhodopsin, a retinal-binding membrane protein, has been recently discovered, however its function remains unknown. Herein, we investigated the relationship between Actinobacteria bacterium IMCC26103 heliorhodopsin (AbHeR) and an adjacent glutamine synthetase (AbGS) in the same operon. We demonstrate that AbHeR binds to AbGS and regulates AbGS activity. More specifically, the dissociation constant (Kd) value of the binding between AbHeR and AbGS is 6.06 μM. Moreover, the absence of positively charged residues within the intracellular loop of AbHeR impacted Kd value as they serve as critical binding sites for AbGS. We also confirm that AbHeR up-regulates the biosynthetic enzyme activity of AbGS both in vitro and in vivo in the presence of light. GS is a key enzyme involved in nitrogen assimilation that catalyzes the conversion of glutamate and ammonia to glutamine. Hence, the interaction between AbHeR and AbGS may be critical for nitrogen assimilation in Actinobacteria bacterium IMCC26103 as it survives in low-nutrient environments. Overall, the findings of our study describe, for the first time, to the best of our knowledge, a novel function of heliorhodopsin as a regulatory rhodopsin with the capacity to bind and regulate enzyme activity required for nitrogen assimilation.

For sustainable crop cultivation in the face of global warming, it is important to unravel the genetic mechanisms underlying plant adaptation to a warming climate and apply this information to breeding. Thermomorphogenesis and ambient temperature signaling pathways have been well studied in model plants, but little information is available for vegetable crops. Here, we investigated genes responsive to warming conditions from two Brassica rapa inbred lines with different geographic origins: subtropical (Kenshin) and temperate (Chiifu). Genes in Gene Ontology categories “response to heat”, “heat acclimation”, “response to light intensity”, “response to oxidative stress”, and “response to temperature stimulus” were upregulated under warming treatment in both lines, but genes involved in “response to auxin stimulus” were upregulated only in Kenshin under both warming and minor-warming conditions. We identified 16 putative high temperature (HT) adaptation-related genes, including 10 heat-shock response genes, 2 transcription factor genes, 1 splicing factor gene, and 3 others. BrPIF4, BrROF2, and BrMPSR1 are candidate genes that might function in HT adaptation. Auxin response, alternative splicing of BrHSFA2, and heat shock memory appear to be indispensable for HT adaptation in B. rapa. These results lay the foundation for molecular breeding and marker development to improve warming tolerance in B. rapa.

Caenorhabditis elegans C09F5.1 is a nematode-specific gene that encodes a type II transmembrane protein containing the BRICHOS domain. The gene was isolated as a heat-sensitive mutant, but the function of the protein remained unclear. We examined the expression pattern and subcellular localization of C09F5.1 as well as its roles in thermotolerance and chaperone function. Expression of C09F5.1 under heat shock conditions was induced in a heat shock factor 1 (HSF-1)–dependent manner. However, under normal growth conditions, most cells types exposed to mechanical stimuli expressed C09F5.1. Knockdown of C09F5.1 expression or deletion of the N-terminal domain decreased thermotolerance. The BRICHOS domain of C09F5.1 did not exhibit chaperone function unlike those of other proteins containing this domain, but the domain was essential for the proper subcellular localization of the protein. Intact C09F5.1 was localized to the Golgi body, but the N-terminal domain of C09F5.1 (C09F5.1-NTD) was retained in the ER. C09F5.1-NTD delayed paralysis by beta-amyloid (1-42) protein (Aβ42) in Alzheimer’s disease model worms (CL4176) and activated the unfolded protein response (UPR) by interacting with Aβ42. An intrinsically disordered region (IDR) located at the N-terminus of C09F5.1 may be responsible for the chaperone function of C09F5.1-NTD. Taken together, the data suggest that C09F5.1 triggers the UPR by interacting with abnormal proteins.