병원균 감염에 대응한 애기장대 PRA1 상동체들의 세포 내 소포체에서의 단백질 조절 기작에 관한 연구

Abstract

In plants, the Arabidopsis thaliana prenylated rab acceptor 1 (AtPRA1) family contains 19 members that display varying degrees of sequence homology to animal PRA1 and localize to the ER and/or endosomes depending on individual members. However, their exact role has not been fully determined. In this study, I selected 14 homologs of prenylated acceptor protein 1 (PRA1)/Yip3 (Figure 3-1) and investigated the expression, localization, and biochemical properties of 14 Arabidopsis homologes of PRA1. The 14 Arabidopsis proteins share 20% to 60% amino acid sequence identity to each other, and display approximately 20% identity to human PRA1/Yip3. Subcellular fractionation experiments demonstrated that transiently expressed AtPRA1s in protoplasts behave as integral membrane proteins. In colocalization experiments with various organellar markers, all 14 transiently expressed AtPRA1 isoforms in protoplasts, and stably expressed AtPRA1.B6 and AtPRA1.B5 in transgenic plants localized to the ER and Golgi complex. Arabidopsis PRA1 isoforms can be divided into several different groups (clade A-clade G). However, it is currently unclear whether this grouping reflects any functional differences among AtPRA isoforms. Using available public microarray data search, I find that Arabidoopsis PRA1 homologues were induced by biotic stresses (http://www. genevestigator. com). In plants, protein trafficking, one of essential cellular processes, appear to be the major battle ground between host cells and infecting pathogens

infecting pathogen attacks the host protein trafficking system to nullify the defense mechanism, whereas host cells appear to modulate the trafficking system to fight against infecting pathogens. However, the exact mechanism by which the host cell modulates its trafficking systems upon pathogen infection is not fully understood. Here I select three Arabidopsis PRA1 homologs AtPRA1.B6, AtPRA1.B5 and AtPRA1.F3 (two is clade B and one is clade F) and demonstrated that those three proteins play critical roles in regulation of trafficking at the ER in response to pathogen infection. AtPRA1.B6 and AtAtPRA1.B5 that localized to the Golgi apparatus with a minor portion to the ER interacted with both Sar1 and Sec23. This interaction resulted in inhibition of heterodimer formation between Sec23 and Sec24, two components of COPII vesicle, and thereby caused differential regulation of protein trafficking at the ER. In the cells, activation of the defense signaling pathway elevated posttranslationally AtPRA1.B5, AtPRA1.B6 and to higher levels, which in turn inhibited trafficking of vacuolar and secretory proteins at the ER and facilitates trafficking of Golgi-localized proteins for carbohydrate biosynthesis and secreted PR proteins. Furthermore, AtPRA1.B6 and AtPRA1.B5 overexpressing plants were more resistant to pathogen infection whereas atatpra1.b5 and atpra1.f3 knock-out mutans displayed increased sensitivity to pathogen infection. Based on these results, I propose that AtPRA1.B5, AtPRA1.B6 and AtPRA1.F3 serve as ER traffic regulators that facilitate trafficking of defense-related proteins in ER when plants are attacked by pathogen.