Moreover, mutant or transgenic plants expressing JAZ1, JAZ3, and JAZ10 lacking the Jas domain exhibit constitutive repression of JA signaling and are insensitive to JA ( Chini et al. The JAZ C-terminal region, including the Jas domain, seems particularly important for controlling the SCF COI1-dependent stability of JAZ proteins because JAZ1 and JAZ3 derivatives lacking this region are no longer degraded in response to JA treatment ( Chini et al., 2007 Thines et al., 2007 Yan et al., 2007). In addition, Thines and coworkers noticed a weakly conserved region at the N-terminus (referred to “NT” hereinafter). 2007).Īll JAZ proteins contain two highly conserved sequence motifs: the TIFXG signature defines the so-called ZIM domain ( Vanholme et al., 2007) in the central portion of the protein, and the C-terminal Jas motif having the consensus sequence SLX 2FX 2KRX 2RX 5PY ( Yan et al., 2007). Several JAZ proteins, including JAZ1, JAZ3, and JAZ6, have been shown to be degraded in Arabidopsis in response to JA treatments and this degradation is dependent on SCF COI1 and the 26S proteasome ( Chini et al. ![]() The cognate substrates of SCF COI1 were identified recently they are members of the JAZ ( jasmonate ZIM-domain) protein family ( Chini et al. E3 ubiquitin ligases are involved in the ubiquitination of specific protein substrates, targeting them to the 26S proteasome for degradation. A critical component of JA signaling is COI1, which is the F-box protein subunit of SCF COI1, a member of the Skip/Cullin/F-box (SCF) family of E 3 ubiquitin ligases ( Xie et al., 1998 Li et al., 2002). Jasmonates regulate a wide range of biological processes in plants, from sexual reproduction to herbivore defense and pathogen responses ( Browse, 2005 Howe and Jander, 2008 Browse and Howe, 2008). ![]() These results not only suggest that coronatine and JA-Ile target the physical interaction between COI1 and the Jas domain of JAZ repressors, but also illustrate a critical role of positively charged amino acids in the Jas domain in mediating JA-Ile/coronatine-dependent JAZ interaction with COI1. Importantly, transgenic Arabidopsis plants expressing JAZ1 carrying these two mutations exhibited JA-insensitive phenotypes, including male sterility and enhanced resistance to P. These two mutations did not affect the ability of JAZ1 and JAZ9 to interact with the transcription factor AtMYC2. Two positively charged amino acid residues in the Jas domain were identified as being essential for coronatine-dependent COI1-JAZ interactions. The carboxyl terminal Jas motif, but not the N-terminal (NT) domain or central ZIM domain of JAZ proteins, is critical for JA-Ile/coronatine-dependent interaction with COI1. Here, we show that coronatine, but not its two biosynthetic precursors, could also promote interaction between Arabidopsis COI1 and multiple JAZ proteins. We recently showed that jasmonoyl-isoleucine (JA-Ile) could promote physical interaction between Arabidopsis JAZ1 and COI1 (the F-box component of SCF COI1) proteins, and that the JA-Ile-dependent COI1-JAZ1 interaction could be reconstituted in yeast cells (i.e., in the absence of other plant proteins). An important step in JA signaling is the SCF COI1 E3 ubiquitin ligase-dependent degradation of JAZ repressor proteins. The structure of coronatine is similar to a class of plant hormones called jasmonates (JAs). Coronatine is an important virulence factor produced by several pathovars of the bacterial pathogen Pseudomonas syringae.
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