Involved in jasmonate (JA) signaling. Required for jasmonate signaling in plant defense responses (PubMed:22529386). Can complement Arabidopsis coi1-1 mutant and restore jasmonate signaling (PubMed:23320078). Component of SCF(COI1) E3 ubiquitin ligase complexes, which may mediate the ubiquitination and subsequent proteasomal degradation of target proteins, including TIFY/JAZ family (By similarity). Interacts with TIFY10C/JAZ8 in a coronatine-dependent manner (PubMed:23104764, PubMed:23320078). Interacts with TIFY3/JAZ1, TIFY6A/JAZ3, TIFY6B/JAZ4, TIFY10A/JAZ6, TIFY10B/JAZ7, TIFY11A/JAZ9, TIFY11B/JAZ10, TIFY11C/JAZ11 and TIFY11D/JAZ12 in a coronatine-dependent manner (PubMed:23320078). Expressed in roots, shoots, leaf sheaths and leaf blades. Plants silencing COI1A and COI1B show increased plant height and seed length, are hypersensitive to gibberellin, and display reduced sensitivity to inhibition of seedling growth by jasmonate.