A Histone Code Reader and a Transcriptional Activator Interact to Regulate Genes for Salt Tolerance

Area of Science:

• Plant molecular biology
• Epigenetics
• Stress physiology

Background:

• Plant homeodomain (PHD) finger proteins are crucial epigenetic readers involved in development and stress responses.
• These proteins typically bind to modified histone tails, interpreting the 'histone code'.

Purpose of the Study:

• To investigate the function of soybean GmPHD6 in stress tolerance.
• To elucidate the mechanism by which GmPHD6 mediates stress response.

Main Methods:

• Analysis of GmPHD6 histone binding specificity (H3K4me0/1/2).
• Assessment of GmPHD6 DNA-binding and transcriptional activity.
• Yeast two-hybrid assays to identify interacting partners (LHP1).
• Transgenic hairy root system in soybean (Glycine max) for overexpression and knockdown studies.
• Gene expression analysis of stress-related genes.

Main Results:

• GmPHD6 binds to low-methylated histone H3K4 (H3K4me0/1/2) via its N-terminal domain, not the PHD finger.
• GmPHD6 possesses DNA-binding ability but lacks intrinsic transcriptional regulatory function.
• GmPHD6 interacts with LHP1 to form a transcriptional activation complex essential for stress tolerance.
• Overexpression of GmPHD6 enhances stress tolerance in soybean, a function dependent on LHP1.
• GmPHD6 regulates numerous stress-related genes, including CYP75B1 and CYP82C4, which also confer stress tolerance upon overexpression.

Conclusions:

• GmPHD6 acts as a histone code reader, recognizing specific histone marks to initiate a stress response pathway.
• The GmPHD6-LHP1 complex is recruited to target gene promoters (e.g., CYP75B1, CYP82C4) where LHP1 activates transcription.
• This study reveals a novel two-partner mechanism for enhancing stress tolerance in soybean, with potential applications in other crops.