wang, n. | Search bioRxiv

bioRxiv2024

Architecture of the ATP-driven motor for protein import into chloroplasts

Thousands of nuclear-encoded proteins are transported into chloroplasts through the TOC-TIC translocon spanning the chloroplast envelope membranes. A motor complex pulls the translocated proteins out of the TOC-TIC complex into the chloroplast stroma by hydrolyzing ATP. The Orf2971-FtsHi complex was suggested to serve as the ATP-hydrolyzing motor in Chlamydomonas reinhardtii, but little is known about its architecture and assembly. Here, we report the 3.2-[A] resolution structure of the Chlamydomonas Orf2971-FtsHi complex. The 20-subunit complex spans the chloroplast inner envelope with two bulky modules protruding into the intermembrane space and stromal matrix. Six subunits form a hetero-hexamer potentially providing the pulling force through ATP hydrolysis. The remaining subunits, including potential enzymes/chaperones, likely facilitate the complex assembly and regulate its proper function. Our results provide the structural foundation for mechanistic understanding of chloroplast protein translocation.

biochemistry↗

bioRxiv2021

Genomic analysis based on chromosome-level genome assembly reveals an expansion of terpene biosynthesis of Azadirachta indica

Azadirachta indica (neem), an evergreen tree of the Meliaceae family, is a source of the potent biopesticide azadirachtin. The lack of a chromosome-level assembly impedes the understanding of in-depth genomic architecture and the comparative genomic analysis of A. indica. Here, a high-quality genome assembly of A. indica was constructed using a combination of data from Illumina, PacBio, and Hi-C technology, which is the first chromosome-scale genome assembly of A. indica. The genome size of A. indica is 281 Mb anchored to 14 chromosomes (contig N50=6 Mb and scaffold N50=19 Mb). The genome assembly contained 115 Mb repetitive elements and 25,767 protein-coding genes. Evolutional analysis revealed that A. indica didnt experience any whole-genome duplication (WGD) event after the core eudicot {gamma} event, but some genes and genome segment might undergo recent duplications. The secondary metabolite clusters, TPS genes, and CYP genes were also identified. Comparative genomic analysis revealed that most of the A. indica-specific TPS genes and CYP genes were located on the terpene-related clusters on chromosome 13. It is suggested that chromosome 13 may play an important role in the specific terpene biosynthesis of A. indica. And the gene duplication events may be responsible for the terpene biosynthesis expansion in A. indica. This will shed light on terpene biosynthesis in A. indica and facilitate comparative genomic research of the family Meliaceae.

genomics↗