The R2R3-MYB Transcription Factor MYB49 Regulates Cadmium Accumulation

Abscisic acid (ABA) reduces accumulation of potentially toxic cadmium (Cd) in plants. How the ABA signal is transmitted to modulate Cd uptake remains largely unclear. Here, we report that the basic region/Leu zipper transcription factor ABSCISIC ACID-INSENSITIVE5 (ABI5), a central ABA signaling molecule, is involved in ABA-repressed Cd accumulation in plants by physically interacting with a previously uncharacterized R2R3-type MYB transcription factor, MYB49. Overexpression of the Cd-induced gene in Arabidopsis ( ) resulted in a significant increase in Cd accumulation, whereas knockout plants and plants expressing chimeric repressors of :ERF-associated amphiphilic repression motif repression domain ( ) exhibited reduced accumulation of Cd. Further investigations revealed that MYB49 positively regulates the expression of the basic helix-loop-helix transcription factors and by directly binding to their promoters, leading to activation of , which encodes a metal transporter involved in Cd uptake. MYB49 also binds to the promoter regions of the heavy metal-associated isoprenylated plant proteins ( ) and , resulting in up-regulation of their expression and subsequent Cd accumulation. On the other hand, as a feedback mechanism to control Cd uptake and accumulation in plant cells, Cd-induced ABA up-regulates the expression of , whose protein product interacts with MYB49 and prevents its binding to the promoters of downstream genes, thereby reducing Cd accumulation. Our results provide new insights into the molecular feedback mechanisms underlying ABA signaling-controlled Cd uptake and accumulation in plants.