Biomolecular phase separation in stress granule assembly and virus infection.

Liquid-liquid phase separation (LLPS) has emerged as a crucial mechanism for cellular compartmentalization. One prominent example of this is the stress granule. Found in various types of cells, stress granule is a biomolecular condensate formed through phase separation. It comprises numerous RNA and RNA-binding proteins. Over the past decades, substantial knowledge has been gained about the composition and dynamics of stress granules. SGs can regulate various signaling pathways and have been associated with numerous human diseases, such as neurodegenerative diseases, cancer, and infectious diseases. The threat of viral infections continues to loom over society. Both DNA and RNA viruses depend on host cells for replication. Intriguingly, many stages of the viral life cycle are closely tied to RNA metabolism in human cells. The field of biomolecular condensates has rapidly advanced in recent times. In this context, we aim to summarize research on stress granules and their link to viral infections. Notably, stress granules triggered by viral infections behave differently from the canonical stress granules triggered by sodium arsenite (SA) and heat shock. Studying stress granules in the context of viral infections could offer a valuable platform to link viral replication processes and host anti-viral responses. A deeper understanding of these biological processes could pave the way for innovative interventions and treatments for viral infectious diseases. They could potentially bridge the gap between basic biological processes and interactions between viruses and their hosts.

Initiation of scutellum-derived callus is regulated by an embryo-like developmental pathway in rice.

In rice (Oryza sativa) tissue culture, callus can be induced from the scutellum in embryo or from the vasculature of non-embryonic organs such as leaves, nodes, or roots. Here we show that the auxin signaling pathway triggers cell division in the epidermis of the scutellum to form an embryo-like structure, which leads to callus formation. Our transcriptome data show that embryo-, stem cell-, and auxin-related genes are upregulated during scutellum-derived callus initiation. Among those genes, the embryo-specific gene OsLEC1 is activated by auxin and involved in scutellum-derived callus initiation. However, OsLEC1 is not required for vasculature-derived callus initiation from roots. In addition, OsIAA11 and OsCRL1, which are involved in root development, are required for vasculature-derived callus formation but not for scutellum-derived callus formation. Overall, our data indicate that scutellum-derived callus initiation is regulated by an embryo-like development program, and this is different from vasculature-derived callus initiation which borrows a root development program.

Rice LEAFY COTYLEDON1 Hinders Embryo Greening During the Seed Development.

LEAFY COTYLEDON1 (LEC1) is the central regulator of seed development in Arabidopsis, while its function in monocots is largely elusive. We generated Oslec1 mutants using CRISPR/Cas9 technology. Oslec1 mutant seeds lost desiccation tolerance and triggered embryo greening at the early development stage. Transcriptome analysis demonstrated that Oslec1 mutation altered diverse hormonal pathways and stress response in seed maturation, and promoted a series of photosynthesis-related genes. Further, genome-wide identification of OsLEC1-binding sites demonstrated that OsLEC1 bound to genes involved in photosynthesis, photomorphogenesis, as well as abscisic acid (ABA) and gibberellin (GA) pathways, involved in seed maturation. We illustrated an OsLEC1-regulating gene network during seed development, including the interconnection between photosynthesis and ABA/GA biosynthesis/signaling. Our findings suggested that OsLEC1 acts as not only a central regulator of seed maturation but also an inhibitor of embryo greening during rice seed development. This study would provide new understanding for the OsLEC1 regulatory mechanisms on photosynthesis in the monocot seed development.

Identification of New ATG8s-Binding Proteins with Canonical LC3-Interacting Region in Autophagosomes of Barley Callus.

Autophagy is essential to maintain cellular homeostasis for normal cell growth and development. In selective autophagy, ATG8 plays a crucial role in cargo target recognition by binding to various adaptors and receptors with the ATG8-interacting motif, also known as the LC3-interacting region (LIR). However, the process of autophagy in the callus, as a proliferating cell type, is largely unknown. In this study, we overexpressed green fluorescent protein (GFP)-ATG8a and GFP-ATG8b transgenic barley callus and checked their autophagic activities. We identified five new ATG8 candidate interactors containing the canonical LIR motif by using immunoprecipitation coupled with mass spectrometry: RPP3, COPE, NCLN, RAE1, and CTSL. The binding activities between these candidate interactors and ATG8 were further demonstrated in the punctate structure. Notably, RPP3 was colocalized in ATG8-labeled autophagosomes under tunicamycin-induced ER stress. GST pull-down assays showed that the interaction between RPP3 and ATG8 could be prevented by mutating the LIRs region of RPP3 or the LIR docking site (LDS) of ATG8, suggesting that RPP3 directly interacted with ATG8 in an LIR-dependent manner via the LDS. Our findings would provide the basis for further investigations on novel receptors and functions of autophagy in plants, especially in the physiological state of cell de-differentiation.

Functional analysis of auxin receptor OsTIR1/OsAFB family members in rice grain yield, tillering, plant height, root system, germination, and auxinic herbicide resistance.

Auxin regulates almost every aspect of plant growth and development and is perceived by the TIR1/AFB auxin co-receptor proteins differentially acting in concert with specific Aux/IAA transcriptional repressors. Little is known about the diverse functions of TIR1/AFB family members in species other than Arabidopsis. We created targeted OsTIR1 and OsAFB2-5 mutations in rice using CRISPR/Cas9 genome editing, and functionally characterized the roles of these five members in plant growth and development and auxinic herbicide resistance. Our results demonstrated that functions of OsTIR1/AFB family members are partially redundant in grain yield, tillering, plant height, root system and germination. Ostir1, Osafb2 and Osafb4 mutants exhibited more severe phenotypes than Osafb3 and Osafb5. The Ostir1Osafb2 double mutant displays extremely severe defects in plant development. All five OsTIR1/AFB members interacted with OsIAA1 and OsIAA11 proteins in vivo. Root elongation assay showed that each Ostir1/afb2-5 mutant was resistant to 2,4-dichlorophenoxyacetic acid (2,4-D) treatment. Notably, only the Osafb4 mutants were strongly resistant to the herbicide picloram, suggesting that OsAFB4 is a unique auxin receptor in rice. Our findings demonstrate similarities and specificities of auxin receptor TIR1/AFB proteins in rice, and could offer the opportunity to modify effective herbicide-resistant alleles in agronomically important crops.