On November 14, 2024, researchers Hang Runlai (first author), Chen Xuemei (Peking University), and You Chenjiang (South China Agricultural University) published a paper titled “HOT3/eIF5B1 Confers Kozak Motif-Dependent Translational Control of Photosynthesis-Associated Nuclear Genes for Chloroplast Biogenesis” in Nature Communications (IF=14.7).
The research, which utilized the Jiupo BPC500H incubator and Jiupo LED Plant Growth Lights under 22°C full-spectrum white light, explores the link between the Kozak motif and the I-E translation switch mediated by eIF5B in the translation process. The study reveals the functional role of HOT3 in cytoplasmic translation control during chloroplast biogenesis and photosynthesis.
Cited Product in the Literature — Jiupo Plant Cultivation Incubator BPC500H
Related paper: https://doi.org/10.1038/s41467-024-54194-1
In this study, the authors utilized ribosome profiling to systematically analyze and compare the ribosome occupancy between wild-type and hot3-2 mutant plants during two key stages of chloroplast development: the early nutrient growth phase and the reproductive flowering phase. These stages involve active chloroplast development. The study highlights the function of HOT3/eIF5B1 in promoting translation initiation switch (I-to-E) across the genome:
- HOT3/eIF5B1 loss-of-function results in significantly increased 80S ribosome stalling at the translation initiation site (TIS), indicating a defect in the I-to-E switch. By comparing the ratio of 80S ribosome signals normalized to TIS and coding sequence (CDS), the authors created the relative Pausing at the Start codon (rPS) index to quantify the efficiency of I-to-E switching across different transcripts.
Figure 1: Ribosome profiling analysis reveals defects in translation initiation to elongation transition in the hot3-2 mutant. - Based on the rPS index, the authors found that the I-to-E conversion efficiency at the TIS is downregulated by more than twofold in transcripts with -3A, +4G, and +5C Kozak motifs in the hot3-2 mutant. By extracting the -3/+4/+5 nucleotide combinations, the authors conducted a comprehensive analysis of I-to-E conversion efficiency for 64 simplified Kozak motifs in wild-type Arabidopsis. Key findings include:
- Different Kozak motifs exhibit varying I-to-E conversion efficiency.
- The most prevalent Kozak motifs, corresponding to the most abundant transcripts, generally show lower median rPS values and higher I-to-E conversion efficiency, suggesting that genes may preferentially select efficient Kozak motifs to enhance translation initiation.
- These trends are conserved across Arabidopsis (Arabidopsis thaliana), rice (Oryza sativa), and wheat (Triticum aestivum).
- The best Kozak motif for Arabidopsis is -3A/+4G/+5C, while for rice and wheat, -3G/+4G/+5C is the most efficient, possibly due to the high GC content in the rice and wheat genomes.
- The genes corresponding to the best Kozak motifs in these three species are enriched in photosynthesis-associated nuclear genes (PhANGs), particularly those encoding photosynthetic proteins on the thylakoid membrane.
Figure 2: Optimal Kozak motifs exhibit higher translation initiation efficiency and are enriched in photosynthetic system genes
- HOT3/eIF5B1 loss-of-function leads to a downregulation in I-to-E conversion efficiency for most Kozak motifs, with the most pronounced effect observed in the A/GC type, further reducing translation efficiency for PhANGs. Using a Dual-LUC luciferase reporter system, the authors demonstrated that HOT3/eIF5B1 promotes the synthesis of thylakoid membrane-associated photosynthetic complex proteins in a Kozak motif-dependent manner, thereby playing a crucial role in chloroplast development and photosynthesis. As such, HOT3/eIF5B1 is not only a translation initiation factor but also plays an important role in regulating chloroplast development and photosynthesis. By promoting the transition from translation initiation to elongation, HOT3/eIF5B1 ensures the efficient expression of photosynthesis-related genes, which is essential for plant growth and adaptation under autotrophic conditions.
Figure 3: HOT3/eIF5B1-mediated cytoplasmic translation initiation is involved in chloroplast development and photosynthesis.
In conclusion, this study uncovers a novel mechanism by which nuclear genes regulate chloroplast development and photosynthesis through cytoplasmic translation initiation. The findings provide new insights for rational design at the level of regulatory elements in synthetic biology and plant molecular factories, offering a theoretical foundation for improving the light efficiency of crops and forage. Optimizing translation efficiency and enhancing photosynthetic capacity could help address challenges posed by climate change and other environmental pressures, thereby improving crop yield and quality.