Structural and functional similarities and differences in nucleolar Pumilio RNA-binding proteins between Arabidopsis and the charophyte Chara corallina.

BACKGROUND: Pumilio RNA-binding proteins are evolutionarily conserved throughout eukaryotes and are involved in RNA decay, transport, and translation repression in the cytoplasm. Although a majority of Pumilio proteins function in the cytoplasm, two nucleolar forms have been reported to have a function in rRNA processing in Arabidopsis. The species of the genus Chara have been known to be most closely related to land plants, as they share several characteristics with modern Embryophyta. RESULTS: In this study, we identified two putative nucleolar Pumilio protein genes, namely, ChPUM2 and ChPUM3, from the transcriptome of Chara corallina. Of the two ChPUM proteins, ChPUM2 was most similar in amino acid sequence (27% identity and 45% homology) and predicted protein structure to Arabidopsis APUM23, while ChPUM3 was similar to APUM24 (35% identity and 54% homology). The transient expression of 35S:ChPUM2-RFP and 35S:ChPUM3-RFP showed nucleolar localization of fusion proteins in tobacco leaf cells, similar to the expression of 35S:APUM23-GFP and 35S:APUM24-GFP. Moreover, 35S:ChPUM2 complemented the morphological defects of the apum23 phenotypes but not those of apum24, while 35S:ChPUM3 could not complement the apum23 and apum24 mutants. Similarly, the 35S:ChPUM2/apum23 plants rescued the pre-rRNA processing defect of apum23, but 35S:ChPUM3/apum24+/- plants did not rescue that of apum24. Consistent with these complementation results, a known target RNA-binding sequence at the end of the 18S rRNA (5'-GGAAUUGACGG) for APUM23 was conserved in Arabidopsis and C. corallina, whereas a target region of ITS2 pre-rRNA for APUM24 was 156 nt longer in C. corallina than in A. thaliana. Moreover, ChPUM2 and APUM23 were predicted to have nearly identical structures, but ChPUM3 and APUM24 have different structures in the 5th C-terminal Puf RNA-binding domain, which had a longer random coil in ChPUM3 than in APUM24. CONCLUSIONS: ChPUM2 of C. corallina was functional in Arabidopsis, similar to APUM23, but ChPUM3 did not substitute for APUM24 in Arabidopsis. Protein homology modeling showed high coverage between APUM23 and ChPUM2, but displayed structural differences between APUM24 and ChPUM3. Together with the protein structure of ChPUM3 itself, a short ITS2 of Arabidopsis pre-rRNA may interrupt the binding of ChPUM3 to 3'-extended 5.8S pre-rRNA.

Differential proteomics of Picrorhiza kurrooa Royle ex Benth. in response to dark stress.

Picrorhiza (Picrorhiza kurrooa Royle ex Benth.) an important medicinal herb of western Himalayan region has been used to treat various diseases and disorders. Over-harvesting and lack of cultivation has led to its entry in Red Data Book as an endangered species. Further, its very restrictive habitat and lesser biomass production are major limitations for bringing it under commercial cultivation. All these issues necessitate deeper insights into mechanisms governing its growth and interaction with the environmental cues. Light may be one of the important factors to be studied for its role in regulating growth and adaptation of Picrorhiza as in natural habitat it prefers shady niches. Keeping this in view, proteome of Picrorhiza kept under light vis-à-vis under dark was analysed and compared. Leaf as well as root proteome of Picrorhiza was studied. Denaturing two dimensional gel electrophoresis and mass spectrometry techniques were used to detect and identify differentially expressed proteins, respectively. Twenty two proteins from leaf and 25 proteins from root showed differential expression levels under dark and light conditions. Among the differentially expressed proteins, majority were those involved in metabolism, protein synthesis, and stress and defense response. Other differentially expressed proteins were those involved in photosynthetic process, photorespiration and few proteins were with unknown function indicating that many different processes work together to establish a new cellular homeostasis in response to dark and light conditions. Proteins found to be differentially expressed under light vis-à-vis dark conditions suggested a range of biochemical pathways and processes being associated with response of plant to dark conditions. The identified proteins may be utilized for developing strategies for improving the biomass production/performance of Picrorhiza under varied light/dark habitats.