The Research On Physiological Functions Regulated By Arabidopsis PUB13 E3 Ubiquitin Ligase Activity

U-box proteins are highly conserved in eukaryon and exist widely in plants. Most of U-box proteins possess E3 ubiquitin ligase activity and involved in various physiological activities. It is reported that the Arabidopsis U-box protein PUB 13 possesses E3 ubiquitin ligase activity, and it synthetically regulates plant cell death, disease resistance and flowering time. However, the molecular mechanism of PUB 13 regulating plant physiological activities is still unknown. Here, the physiological functions of PUB 13 E3 ubiquitin ligase activity in Arabidopsis were investigated, and the results are as following:1. The E3 ubiquitin ligase activity is suppressed obviously once the conserved amino acid Valine273 in the U-box domain of PUB13 is mutated to Arginine273 (i.e. PUB13V273R) To make clear the physiological functions of PUB 13 E3 ubiquitin ligase activity, the PUB13V73R/publ3 transgenic plants were constructed.2. The PUB13V273R/publ3 transgenic plants are dwarf and the leaves size is smaller than control under short day condition. However, this phenotype is not obvious under long day and middle day conditions. Moreover, comparing with wild type Col-0, the transgenic plants display early flowering under long day and middle day conditions. Accordingly, the transcription level of flowering positive regulator FT and SOC1 genes in PUB13V273R/publ3 plants is obviously higher than in Col-0.3. The UB13V273R/publ3 transgenic plants present lesion mimic phenotype under long day and middle day conditions, and the Trypan blue staining showed that the transgenic plants spontaneously activate a large number of cell death.4. The PUB13V73R/publ3 transgenic plants are more resistant against biotrophic pathogens Erysiphe cichoracearum UCSC1 and Pseudomonas syringae pv. maculicola ES4326, oppositely, the plants decrease the resistance to necrotrophic pathogen Botrytis cinerea BO5-10. Correspondingly, transcription level of marker gene PR1 in the SA pathway which is responsible for resisting biotrophic pathogens is enhanced in PUB13V273R/publ3 plants, but the marker gene PDF1.2 in JA/ET pathway which regulates resistance to necrotrophic pathogens is suppressed.The above results proved that the PUB13 E3 ubiquitin ligase synthetically regulates signaling transduction of Arabidopsis development (i.e. plants and leaves size, flowering time), cell death and disease resistance. The research results of this paper give an important clue for illuminating the physiological functions and their molecular mechanism of plant U-box protein and ubiquitination.