Cadmium (Cd) is a nonnutrient metal that is potentially toxic even at low concentrations in plants. Abscisic acid (ABA) reduces accumulation of Cd in plants. However, how ABA signaling affects Cd uptake by modulating IRT1 expression remains largely unclear.

In a recent study published online in Plant Physiology, researchers at Xishuangbanna Tropical Botanical Garden (XTBG) of Chinese Academy of Sciences reported that the basic region/leucine zipper TF ABSCISIC ACID141 INSENSITIVE5 (ABI5) is involved in Cd accumulation.

The ABI5, as a central ABA signaling molecule, is involved in ABA-repressed Cd accumulation in plants by physically interacting with a previously uncharacterized R2R3-MYB transcription factor MYB49.

Overexpression of ABI5 reduces, whereas loss of function in the abi5 mutant increases, Cd accumulation in Arabidopsis, indicating the involvement of ABI5 in modulating Cd uptake.

To identify transcriptional regulators involved in ABI5-mediated Cd accumulation, researchers searched for ABI5-interacting proteins and identified the Cd-induced R2R3-MYB TF MYB49.

They also examined the function and the roles of an uncharacterized R2R3-MYB member, MYB49, in Arabidopsis, they found that Arabidopsis MYB49 regulates Cd accumulation by directly regulating bHLH38, bHLH101, HIPP22, and HIPP44 expression.

Considering that Cd toxicity induces endogenous ABA accumulation in plants, researchers suggested that a feedback mechanism based on physical interactions between MYB49 and ABI5 controls Cd uptake and accumulation in plant cells.

"The results enabled us to understand the mechanisms underlying plant response to Cd stress through the actions of MYB49 and ABI5,” said Prof. XU Jin, principal investigator of this study.

ABI5 interacts with MYB49 and represses its function by preventing its binding to the downstream genes bHLH38, bHLH101, HIPP22, and HIPP44, resulting in inactivation of IRT1 and reduced Cd uptake. (Image by XTBG)