Figure 5.

ABA signaling mediated by the plastid-localized CHLH protein.

The H subunit of MgCheletase spans the outer chloroplast membrane. It can associate with 3 other subunits (CHLI, CHLD, and GUN4) to function in synthesis of Mg-ProtophyrinIX (Mg-ProtoIX) within the plastid. Alternatively, in association with CHLI, the C-terminus of CHLH can bind WRKY40 in the cytosol (and, to a lesser extent, WRKY 18 and 60). CHLH/WRKY binding is enhanced by ABA, such that these WRKYs are greatly depleted in nuclei, thereby derepressing several transcription factors that positively regulate ABA-induced gene expression.