A rice group F2 PP2C gene, OsPP18, was characterized as a target gene of the transcription factor SNAC1.
- SNAC1 can bind to the promoter of the OsPP18 gene and activates its expression. The expression of OsPP18 was significantly down-regulated in the SNAC1-amiRNA transgenic plants with the expression of SNAC1 suppressed, which indicates that the expression of OsPP18 is positively regulated by SNAC1.
- Although OsPP18 is a typical PP2C with enzymatic activity, it did not interact with SnRK2 protein kinases which function in ABA signaling. Meanwhile, the expression of ABA-responsive genes was not affected in the ospp18 mutant, and the ABA sensitivity of the ospp18 mutant and OsPP18-over-expressing plants was not altered either.
- In the presence of the phosphorylated peptide substrate, GST-OsPP18, but not GST alone, catalyzed the release of phosphate. This reaction was inhibited by the serine/threonine phosphatase inhibitor, sodium fluoride (NaF), but not by vanadate, a tyrosine phosphatase inhibitor. OsPP18 enzyme activity was detected only in PP2C buffer but not in PP2A and PP2B buffers, which demonstrates that OsPP18 encodes an enzymatically active PP2C.
- Overall, OsPP18 is a novel PP2C gene which is regulated by SNAC1 and confers drought and oxidative stress tolerance by regulating ROS homeostasis through ABA-independent pathways.
- a T-DNA insertion mutant:
- The ospp18 mutant was more sensitive than wild-type plants to drought stress at both the seedling and panicle development stages. Rice plants with OsPP18-suppresed via artificial microRNA were also hypersensitive to drought stress.
- Microarray analysis of the mutant revealed that genes encoding reactive oxygen species (ROS) scavenging enzymes were down-regulated in the ospp18 mutant, and the mutant exhibited reduced activities of ROS-scavenging enzymes and increased sensitivity to oxidative stresses.
- The OsPP18 transcript level strongly increased after drought stress, but was not significantly changed under other stress treatments. The expression level of OsPP18 was repressed under submergence treatment. Under various phytohormone treatments, OsPP18 was transiently induced only by jasmonic acid (JA) and salicylic acid (SA), and of special note, it was not induced by ABA.
- Over-expression of OsPP18 in rice led to enhanced osmotic and oxidative stress tolerance. The expression of OsPP18 was induced by drought stress, but not induced by abscisic acid.
According to Plant-mPLoc, OsPP18 was predicted to be located in chloroplast, cytoplasm, and nucleus. Yellow fluorescence produced by OsPP18-YFP overlapped with cyan fluorescence produced by CFP, and partly overlapped with cyan fluorescence produced by CFP-GHD7, but did not overlap with the autofluorescence of chlorophyll, which indicated that OsPP18 is targeted to the cytoplasm and nucleus.
OsPP18 belongs to the group F2 of the PP2C gene family in rice according to Singh et al..There are 5 PP2Cs from Arabidopsis and 7 PP2Cs from rice in the group F2. Sequence alignment of the PP2C domain of OsPP18 with other evolutionarily related phosphatases also suggests that OsPP18 belongs to group F2 rather than group A which contains ABI1, ABI2, HAB1, and HAB2, which are known as negative regulators of ABA signaling. OsPP18 and Arabidopsis WIN2 are in the same cluster (with 83% identity to WIN2). WIN2 interacts with HopW1-1 which is a modular P. syringae Avr effector for eliciting a resistance response in Arabidopsis, and is partially required for HopW1-1-induced disease resistance.
Exploration of protein phosphatase gene family in rice has resulted in the identification of 132 members, which can be further divided into different classes phylogenetically. Expression profiling and analysis indicate the involvement of this large gene family in a number of signaling pathways triggered by abiotic stresses and their possible role in plant development.
Labs working on this gene
- National Key Laboratory of Crop Genetic Improvement and National Center of Plant Gene Research (Wuhan), Huazhong Agricultural University, Wuhan, 430070, China
- You J, Zong W, Hu H, et al. A SNAC1-regulated protein phosphatase gene OsPP18 modulates drought and oxidative stress tolerance through ABA-independent reactive oxygen species scavenging in rice[J]. Plant Physiology, 2014: pp. 114.251116.
- Singh A, Giri J, Kapoor S, et al. Protein phosphatase complement in rice: genome-wide identification and transcriptional analysis under abiotic stress conditions and reproductive development[J]. BMC genomics, 2010, 11(1): 435.
- Lee M W, Jelenska J, Greenberg J T. Arabidopsis proteins important for modulating defense responses to Pseudomonas syringae that secrete HopW1‐1[J]. The Plant Journal, 2008, 54(3): 452-465.