The Rice GLYCINE-RICH PROTEIN 3 Confers Drought Tolerance by Regulating mRNA Stability of ROS Scavenging-Related Genes

BACKGROUND

Plant glycine-rich proteins are categorized into several classes based on their protein structures. The glycine-rich RNA binding proteins (GRPs) are members of class IV subfamily possessing N-terminus RNA-recognition motifs (RRMs) and proposed to be involved in post-transcriptional regulation of its target transcripts. GRPs are involved in developmental process and cellular stress responses, but the molecular mechanisms underlying these regulations are still elusive.

RESULTS

Here, we report the functional characterization of rice GLYCINE-RICH PROTEIN 3 (OsGRP3) and its physiological roles in drought stress response. Both drought stress and ABA induce the expression of OsGRP3. Transgenic plants overexpressing OsGRP3 (OsGRP3^OE) exhibited tolerance while knock-down plants (OsGRP3^KD) were susceptible to drought compared to the non-transgenic control. In vivo, subcellular localization analysis revealed that OsGRP3-GFP was transported from cytoplasm/nucleus into cytoplasmic foci following exposure to ABA and mannitol treatments. Comparative transcriptomic analysis between OsGRP3^OE and OsGRP3^KD plants suggests that OsGRP3 is involved in the regulation of the ROS related genes. RNA-immunoprecipitation analysis revealed the associations of OsGRP3 with PATHOGENESIS RELATED GENE 5 (PR5), METALLOTHIONEIN 1d (MT1d), 4,5-DOPA-DIOXYGENASE (DOPA), and LIPOXYGENASE (LOX) transcripts. The half-life analysis showed that PR5 transcripts decayed slower in OsGRP3^OE but faster in OsGRP3^KD, while MT1d and LOX transcripts decayed faster in OsGRP3^OE but slower in OsGRP3^KD plants. H₂O₂ accumulation was reduced in OsGRP3^OE and increased in OsGRP3^KD plants compared to non-transgenic plants (NT) under drought stress.

CONCLUSION

OsGRP3 plays a positive regulator in rice drought tolerance and modulates the transcript level and mRNA stability of stress-responsive genes, including ROS-related genes. Moreover, OsGRP3 contributes to the reduction of ROS accumulation during drought stress. Our results suggested that OsGRP3 alleviates ROS accumulation by regulating ROS-related genes' mRNA stability under drought stress, which confers drought tolerance.

AtC3H18L is a stop-codon read-through gene and encodes a novel non-tandem CCCH zinc-finger protein that can form cytoplasmic foci similar to mRNP granules

The membraneless messenger ribonucleoprotein (mRNP) granules, including processing bodies (PBs) and stress granules (SGs), are important cytoplasmic structures in eukaryotes that can participate in gene expression through mRNA regulation. It has been verified that mRNP granules are mainly composed of proteins and translation-repressed mRNAs. Here, we reported a stop-codon read-through gene, At3g52980, in plants for the first time. At3g52980 encodes a novel non-tandem CCCH zinc-finger (non-TZF) protein named AtC3H18-Like (AtC3H18L), which contains two putative RNA-binding domains. By using transient expression system, we showed that heat treatment can induce the aggregation of diffuse distributed AtC3H18L to form cytoplasmic foci, which were similar to PBs and SGs in morphology. Further analysis did find that AtC3H18L can co-localize with markers of PB and SG. The aggregation of AtC3H18L was closely related to the cytoskeleton, and AtC3H18L-foci were highly dynamic and can move frequently along cytoskeleton. Moreover, analysis in transgenic plants showed that AtC3H18L was specifically expressed in pollen and can form cytoplasmic foci without heat treatment. It will be fascinating in future studies to discover whether and how AtC3H18L affects pollen development by participating in the assembly of mRNP granules as a protein component, especially under heat stress.

Axonemal dynein assembly requires the R2TP complex component Pontin

Pontin (Ruvbl1) and Reptin (Ruvbl2) are closely related AAA ATPases. They are components of the Ruvbl1-Ruvbl2-Tah1-Pih1 (R2TP) complexes that function as co-chaperones for the assembly of multiple macromolecular protein complexes. Here, we show that Pontin is essential for cilia motility in both zebrafish and mouse and that Pontin and Reptin function cooperatively in this process. Zebrafish pontin mutants display phenotypes tightly associated with cilia defects, and cilia motility is lost in a number of ciliated tissues along with a reduction in the number of outer and inner dynein arms. Pontin protein is enriched in cytosolic puncta in ciliated cells in zebrafish embryos. In mouse testis, Pontin is essential for the stabilization of axonemal dynein intermediate chain 1 (DNAI1) and DNAI2, the first appreciated step in axonemal dynein arm assembly. Strikingly, multiple dynein arm assembly factors show structural similarities to either Tah1 or Pih1, the other two components of the R2TP complex. Based on these results, we propose that Pontin and Reptin function to facilitate dynein arm assembly in cytosolic foci enriched with R2TP-like complexes.