The endosperm provides nutrients and growth regulators to the embryo during seed development. LEAFY COTYLEDON1 (LEC1) has long been known to be essential for embryo maturation. LEC1 is expressed in both the embryo and the endosperm; however, the functional relevance of the endosperm-expressed LEC1 for seed development is unclear. Here, we provide genetic and transgenic evidence demonstrating that endosperm-expressed LEC1 is necessary and sufficient for embryo maturation. We show that endosperm-synthesized LEC1 is capable of orchestrating full seed maturation in the absence of embryo-expressed LEC1. Inversely, without LEC1 expression in the endosperm, embryo development arrests even in the presence of functional LEC1 alleles in the embryo. We further reveal that LEC1 expression in the endosperm begins at the zygote stage and the LEC1 protein is then trafficked to the embryo to activate processes of seed maturation. Our findings thus establish a key role for endosperm in regulating embryo development.

NUCLEOPORIN1 (NUP1), a member of the Nuclear Pore Complex (NPC), is located on the inner side of the nuclear membrane. It is highly expressed in seeds; however, its role in seeds including germination has not been explored yet. Here, we identified an abscisic acid (ABA) hypersensitive phenotype of nup1 during germination. ABA treatment drastically changes the expression pattern of thousands of genes in nup1 , including the major transcription factors (TFs) involved in germination, ABI3 , ABI4 , and ABI5 . Double mutant analysis of NUP1 and these ABA-related genes showed that mutations in ABI5 can rescue the phenotype of nup1 , suggesting that NUP1 acts upstream of ABI5 to regulate seed germination. ABI5, a key negative regulator of germination, is abundant in dry seeds and rapidly degrades during germination. However, its spatiotemporal regulation and interaction with other molecular players during degradation remained to be fully elucidated. We found that NUP1 is physically associated with ABI5 and the 26S proteasome. Mutation in NUP1 delayed ABI5 degradation through its post-translational retention in nucleolus under abiotic stress. Taken together, our findings suggest that NUP1 anchors the proteasome to NPC and modulates seed germination through proteasome-mediated degradation of ABI5 in the vicinity of NPC in the nucleoplasm.

RNA has been established as an essential molecule in virtually all cellular processes. Besides its role in cellular modulation via extracellular vesicular release, it has long been thought to only exert its function intracellularly. Recent discoveries have shown evidence of extracellular RNA tethered to the cell surface of different cell types. These cell surface RNAs are predominantly modified with sialylated glycans, denominating them cell surface glycoRNAs. While the expression of cell surface glycoRNAs has been found on a wide array of immune cell and cancer cell types, research on its functional roles has only recently been explored due to challenges in detection, isolation, and sequencing of this new subclass of RNA. In this review, the history, biogenesis, detection and isolation techniques, and functional roles of cell surface RNA to date will be discussed, in addition to commenting on its translational capacity for studying immunomodulation and disease. Acknowledging the presence of cell surface RNAs and propelling our understanding on their function will provide a new avenue to study cellular modulation and cell–cell communication.

Fatty acid desaturase 12 (FAD12) is a key enzyme in fatty acid biosynthesis, responsible for converting oleic acid to linoleic acid through desaturase activity. Euglena gracilis (Euglena) is an emerging platform for the industrial production of various metabolites, including lipids. However, a comprehensive understanding of Euglena’s fatty acid biosynthesis pathways remains incomplete, posing a significant barrier to the commercialization of Euglena bioproducts. To address this gap, we employed a bioinformatics approach to identify a Euglena gracilis FAD12 (Eg FAD12). We analyzed the evolutionary relationship of Eg FAD12 with its homologs from other organisms and revealed that the three canonical histidine box motifs are conserved among FAD12s. To characterize EgFAD12, we cloned it into the pEAQ-hyperstrans vector and overexpressed it in Nicotiana benthamiana to take advantage of its endogenous fatty acid pool, which could act as a substrate. The heterologous expression of FAD12 in N. benthamiana led to an increased linoleic acid content, demonstrating the suspected desaturase activity. To further confirm the function of Eg FAD12, we performed CRISPR-Cas9-mediated knockout of Eg FAD12 in Euglena, which resulted in a drastic reduction in linoleic acid (C18:2) without compromising biomass yield or lipid content. This work advances our understanding of fatty acid biosynthesis in Euglena and will aid in its adoption as a platform for producing customized lipids.

The male germ unit (MGU) in Arabidopsis pollen is comprised of one vegetative nucleus (VN) and two sperm nuclei (SN). It is evolutionarily specialized to deliver immotile sperm nuclei to an ovule for fertilization. Despite some progress in research on MGU, its organization and transport remain only partially understood. Here, we identified Nucleoporin1/136 as a new player in the structural organization and positioning of MGU in pollen tubes. We and others have previously reported the reduced fertility of nup1-1 plants; however, the mechanism remains unknown. In this work, we further examined the role of NUP1 in fertility using two mutant alleles, nup1-1 and nup1-2-/+. The reciprocal crosses between the nup1 mutants and the Col-0 wild type indicate that the nup1 mutant pollen is defective. To study the effect of a complete NUP1 knockout on pollen, we generated a transgenic line that produces pollen with and without NUP1 expression. This work led to the surprising discovery that the NUP1 protein is inherited from the pollen mother cell to the daughter cell during microgametophyte development. Subsequent in vitro experiments showed that NUP1 is required for pollen germination and pollen tube elongation. Further microscopic studies demonstrated that NUP1 is highly expressed in VN and essential for maintaining nuclear shape and size. We also demonstrated that NUP1 is required for proper MGU organization and transport, likely through maintaining VN morphology. Notably, our finding of nuclear morphology-mediated regulation of MGU may also explain the mechanistic details underlying the defective MGU movement in previously reported mutants such as kaku4, wit, and wip, which have abnormal nuclear morphology.

Fatty acid desaturase 12 (FAD12) is a key enzyme in fatty acid biosynthesis, responsible for converting oleic acid to linoleic acid through desaturase activity. Euglena gracilis (Euglena) is an emerging platform for the industrial production of various metabolites, including lipids. However, a comprehensive understanding of Euglena’s fatty acid biosynthesis pathways remains incomplete, posing a significant barrier to the commercialization of Euglena bioproducts. To address this gap, we employed a bioinformatics approach to identify a Euglena gracilis FAD12 ( Eg FAD12). We analyzed the evolutionary relationship of Eg FAD12 with its homologs from other organisms and revealed that the three canonical histidine box motifs are conserved among FAD12s. To characterize Eg FAD12, we cloned it into the pEAQ-hyperstrans vector and overexpressed it in Nicotiana benthamiana to take advantage of its endogenous fatty acid pool, which could act as substrates. The heterologous expression of FAD12 in N. benthamiana led to an increased linoleic acid content, demonstrating the suspected desaturase activity. To further confirm the function of Eg FAD12, we performed CRISPR-Cas9-mediated knockout of Eg FAD12 in Euglena, which resulted in a drastic reduction in linoleic acid (C18:2) without compromising biomass yield or lipid content. This work advances our understanding of fatty acid biosynthesis in Euglena and will aid in its adoption as a platform for producing customized lipids.