Hierarchical transcription factor and regulatory network for drought response in Betula platyphylla.

Although many genes and biological processes involved in abiotic stress response have been identified, how they are regulated remains largely unclear. Here, to study the regulatory mechanism of birch (Betula platyphylla) responding to drought induced by polyethylene glycol (PEG) 6000 (20%, w/v), a partial correlation coefficient-based algorithm for constructing gene regulatory network (GRN) was proposed, and a three-layer hierarchical GRN was constructed, including 68 transcription factors (TFs), and 252 structural genes. Totally, 1448 predicted regulatory relationships are included, and most of them are novel. The reliability of GRN was verified by ChIP-PCR and qRT-PCR based on transient transformation. About 55% of genes in the bottom layer of GRN could confer drought tolerance. We selected the two TFs, BpMADS11 and BpNAC090, from the up layer and characterized their function in drought tolerance. Overexpression of BpMADS11 and BpNAC090 both reduces electrolyte leakage, ROS and MDA contents, displaying increased drought tolerance than wild-type birch. According to this GRN, the important biological processes involved in drought were identified, including "signaling hormone pathways", "water transport", "regulation of stomatal movement" and "response to oxidative stress". This work indicated that BpERF017, BpAGL61 and BpNAC090 are the key upstream regulators in birch drought tolerance. Our data clearly revealed the upstream regulators and TF-DNA interaction regulate different biological processes to adapt drought stress.