Chromosome-level genome assembly of Pedicularis kansuensis illuminates genome evolution of facultative parasitic plant.

Parasitic plants have a heterotrophic lifestyle, in which they withdraw all or part of their nutrients from their host through the haustorium. Despite the release of many draft genomes of parasitic plants, the genome evolution related to the parasitism feature of facultative parasites remains largely unknown. In this study, we present a high-quality chromosomal-level genome assembly for the facultative parasite Pedicularis kansuensis (Orobanchaceae), which invades both legume and grass host species in degraded grasslands on the Qinghai-Tibet Plateau. This species has the largest genome size compared with other parasitic species, and expansions of long terminal repeat retrotransposons accounting for 62.37% of the assembly greatly contributed to the genome size expansion of this species. A total of 42,782 genes were annotated, and the patterns of gene loss in P. kansuensis differed from other parasitic species. We also found many mobile mRNAs between P. kansuensis and one of its host species, but these mobile mRNAs could not compensate for the functional losses of missing genes in P. kansuensis. In addition, we identified nine horizontal gene transfer (HGT) events from rosids and monocots, as well as one single-gene duplication events from HGT genes, which differ distinctly from that of other parasitic species. Furthermore, we found evidence for HGT through transferring genomic fragments from phylogenetically remote host species. Taken together, these findings provide genomic insights into the evolution of facultative parasites and broaden our understanding of the diversified genome evolution in parasitic plants and the molecular mechanisms of plant parasitism.

Development of a split fluorescent protein-based RNA live-cell imaging system to visualize mRNA distribution in plants.

BACKGROUND: RNA live-cell imaging systems have been used to visualize subcellular mRNA distribution in living cells. The RNA-binding protein (RBP)-based RNA imaging system exploits specific RBP and the corresponding RNA recognition sequences to indirectly label mRNAs. Co-expression of fluorescent protein-fused RBP and target mRNA conjugated with corresponding RNA recognition sequences allows for visualizing mRNAs by confocal microscopy. To minimize the background fluorescence in the cytosol, the nuclear localization sequence has been used to sequester the RBP not bound to mRNA in the nucleus. However, strong fluorescence in the nucleus may limit the visualization of nucleus-localized RNA and sometimes may interfere in detecting fluorescence signals in the cytosol, especially in cells with low signal-to-noise ratio. RESULTS: We eliminated the background fluorescence in the nucleus by using the split fluorescent protein-based approach. We fused two different RBPs with the N- or C-terminus of split fluorescent proteins (FPs). Co-expression of RBPs with the target mRNA conjugated with the corresponding RNA recognition sequences can bring split FPs together to reconstitute functional FPs for visualizing target mRNAs. We optimized the system with minimal background fluorescence and used the imaging system to visualize mRNAs in living plant cells. CONCLUSIONS: We established a background-free RNA live-cell imaging system that provides a platform to visualize subcellular mRNA distribution in living plant cells.

Mobile RNAs and proteins: Prospects in storage organ development of tuber and root crops.

Storage tuber and root crops make up a significant portion of the world's subsistence food supply. Because of their importance in food security, yield enhancement has become a priority. A major focus has been to understand the biology of belowground storage organ development. Considerable insights have been gained studying tuber development in potato. We now know that two mobile signals, a full-length mRNA, StBEL5, and a protein, StSP6A, play pivotal roles in regulating tuber development. Under favorable conditions, these signals move from leaves to a belowground modified stem (stolon) and regulate genes that activate tuberization. Overexpression of StBEL5 or StSP6A increases tuber yield even under non-inductive conditions. The mRNAs of two close homologs of StBEL5, StBEL11 and StBEL29, are also known to be mobile but act as repressors of tuberization. Polypyrimidine tract-binding proteins (PTBs) are RNA-binding proteins that facilitate the movement of these mRNAs. Considering their role in tuberization, it is possible that these mobile signals play a major role in storage root development as well. In this review, we explore the presence of these signals and their relevance in the development and yield potential of several important storage root crops.