Plant biology

The Jasmonate Receptor Is Complex

Science Signaling  23 Nov 2010:
Vol. 3, Issue 149, pp. ec355
DOI: 10.1126/scisignal.3149ec355

Jasmonates, plant hormones implicated in defense and development, signal through COI1 (CORONATINE INSENSITIVE1), a component of the Skp-Cullin-F-box ubiquitin E3 ligase complex SCFCOI1, to promote the ubiquitylation and consequent degradation of JAZ (JASMONATE ZIM DOMAIN) transcriptional repressors. Using an in vitro radioligand binding assay, Sheard et al. determined that 3H-coronatine, which resembles jasmonyl-L-isoleucine (JA-Ile), showed specific high-affinity binding to COI1-ASK1 (Arabidopsis Skp1-like protein 1) in the presence of JAZ6 or JAZ1 but only marginal binding in their absence (and no binding to JAZ proteins in the absence of COI1). Analyses of the ability of synthetic JAZ1 peptides to promote 3H-coronatine binding to COI1 led to the identification of a minimal sequence within the JAZ protein C-terminal Jas motif (Glu200 to Val220) as the JAZ1 degron. Analyses of the crystal structure of the COI1-ASK-1-JAZ1 degron peptide complex bound to coronatine or JA-Ile revealed a ligand-binding pocket in COI1. The JAZ1 degron peptide formed a bipartite structure to interact with both COI1 and the ligand, covering the opening of the pocket and thereby trapping the ligand. Mass spectrometry analyses revealed that a small molecule copurified with the COI1-ASK1 complex, which turned out to be inositol-1,2,4,5,6-pentakisphosphate [Ins(1,2,4,5,6)P5]. When Ins(1,2,4,5,6)P5 was stripped by extensive dialysis, COI1-ASK1 alone failed to bind 3H-coronatine and showed little ligand binding even in the presence of JAZ1. Restoration of Ins(1,2,4,5,6)P5, however, rescued 3H-coronatine binding. The authors thus conclude that COI1, the JAZ degron, and Ins(1,2,4,5,6)P5 act as a three-molecule jasmonate co-receptor complex.

L. B. Sheard, X. Tan, H. Mao, J. Withers, G. Ben-Nissan, T. R. Hinds, Y. Kobayashi, F.-F. Hsu, M. Sharon, J. Browse, S. Y. He, J. Rizo, G. A. Howe, N. Zheng, Jasmonate perception by inositol-phosphate-potentiated COI1-JAZ co-receptor. Nature 468, 400–405 (2010). [PubMed]