Functional insights into protein trafficking in plants
To date, significant progress has been made in deciphering NPC structure in vertebrate and yeast cells. The NPC is the largest multiprotein complex that these cells contain. It is composed of multiple copies of about 30 different proteins, which scientists call nucleoporins. On the other hand, the molecular structure and physiological function of nucleoporins in plants remains poorly understood. Scientists initiated the EU-funded project PLANTNPC (Functional characterisation of the plant nuclear pore complex) to fill this knowledge gap. The aim was to improve the current understanding of how the NPC impacts different signalling pathways through the identification of a range of nucleoporin mutant plants. These mutants can offer insights into how protein transport affects the response to hormonal, abiotic and biotic stresses. To this end, the researchers examined the phenotypes of a broad range of nucleoporin mutant plants. They looked into the nuclear morphology as well as the messenger RNA (mRNA) accumulation and found that the nucleus shape is not consistent in all mutants. Certain nucleoporin mutants had more round nuclei than others. More surprisingly was the finding that different amounts of nuclear mRNA accumulate in these mutants. The amount of mRNA accumulated was estimated with a new method that also allowed defining how different subcomplexes contribute to the export of nuclear macromolecules. To further investigate the role of the NPC in mRNA export, the researchers relied on RNA sequencing. RNA was isolated from ribosome and polysome fractions to find which transcripts are exported differentially from the nucleus in different mutants. Analysis of the large data set created is currently underway. The results are expected to provide valuable insights into the function of the NPC as well as the specificity that occurs at the level of the NPC. Follow-up research will provide information about the specific proteins whose nuclear transport is altered in response to pathogens, cold and hormones. PLANTNPC has addressed some of the challenges faced by researchers in the nascent field focused on plant NPC and how defects in the NPC affect gene expression. The current understanding has also been summarised in a review paper published in the Journal of Experimental Botany.
Keywords
Protein trafficking, plants, nuclear pore complex, RNA, nucleoporins, PLANTNPC
