Fig 4.

A) Combined genome-wide association results and Populus co-expression analyses, with Populus homologs of Arabidopsis-tested transcription factors, in a proposed regulatory network. Gold boxes are Populus homologs of Arabidopsis-tested transcription factors; green boxes are GWAS identified Populus genes associated with callus formation. Red edges indicate positive co-expression, blue edges indicate negative co-expression. B) The CNDbr, which negatively co-expressed with LEC2, was down-regulated in Populus leaf protoplasts when overexpressing LEC2. The other three genes (SOK1, MAPK3, and RPD3), positively co-expressed with LEC2, were not detected by qRT-PCR. Ctrl refers to the endogenous expression level of CNDbr in protoplasts while OE_LEC2 refers to the expression level of CNDbr when LEC2 was overexpressed in 3 independent replicates. The expression level of CNDbr was normalized to the ubiquitin internal control. C) Expression patterns of five selected genes in co-expression network. LEC2 has extremely low abundance in leaves while CNDbr was highly expressed in leaves. SOK1, MAPK3, and RPD3 showed low abundances in leaf tissues.