Figure 9.

Bidirectional communication between the chloroplast and the nucleus. Changes in the functional states/activities of plastids caused by high Glc can possibly act as a retrograde signal to alter the expression of nuclear genes such as ABI3, ABI4, ABI5, and HXK1. In particular, the transcription factor ABI4, which likely binds directly to the CCAC/ACGT core element of the GIG/PAA1 promoter, regulates the expression of the plastidial Cu transporter PAA1 that is essential for plastid function and/or activity.