The plant hormone abscisic acid (ABA) regulates many aspects of plant development and stress response. The ubiquitin/26S proteasome pathway plays a very important role in hormone signaling. Since the identification of ABA receptor, considerable progress has been made in understanding ABA signaling pathway. However, the mechanism of endoplasmic membrane (ER) in mediating the signal from ABA perception to transcription factor remains unknown.
Early studies of XIE Qi’s lab at Institute of Genetics and Developmental Biology of Chinese Academy of Sciences, isolated a RING type ubiquitin ligase SDIR1 (SALT- AND DROUGHT-INDUCED REALLY INTERESTING NEW GENE FINGER1). SDIR1 enhances ABA signal by increasing the expression of a serious of bZIP transcription factor, and regulates tolerant ability of plant to drought and salt stress (Zhang et al., 2007, Plant Cell). After that, XIE’s lab attempted to make a further study of SDIR1’s function by isolation its direct substrate.
Using yeast two-hybrid screening, the researchers identified SDIRIP1 (SDIR1-INTERACTING PROTEIN1) as a substrate of SDIR1. Cell biology assays indicated that SDIR1 is localized on ER membrane, the C-terminus of SDIR1, which includes RING domain, faces the cytoplasm and SDIRIP1 is localized to the chloroplast, cell periphery and nucleus. Using biochemistry, cell biology and genetic approaches, they demonstrated that the SDIRIP1 negatively regulates ABA signaling by suppress the expression of ABI5, and C-terminus of SDIR1 can interact with SDIRIP1, and promote SDIRIP1’s degradation through ubiquitin/26Sproteasome pathway.
This study uncovered the function of SDIR/SDIRIP1 in ABA pathway, and provided some clues on the study of communication signals among different organelles.
This work entitled "The RING Finger Ubiquitin E3 Ligase SDIR1 Targets SDIR1-INTERACTING PROTEIN1 for Degradation to Modulate the Salt Stress Response and ABA Signaling in
Arabidopsis" has been published on
the Plant Cell .
This research was supported by 973 Program Grant from the National Basic Research Program of China and Grant from the National Science Foundation of China.
