Senior Staff Scientist Oak Ridge National Laboratory Oak Ridge, Tennessee
Body of Abstract: Phenotypic variation can be due to sequence polymorphism that produces altered or absent proteins and/or due to differences in gene expression that generate varying amounts of protein. To identify genetic factors controlling the complex trait of secondary cell wall biosynthesis in Populus, we performed RNAseq analysis of developing xylem samples collected from the P. trichocarpa × P. deltoides pseudo-backcross mapping pedigree. By using transcript level as a phenotypic trait in the expression Quantitative Trait Locus (eQTL) mapping, we have identified numerous cis- and trans-eQTLs. When overlaying the outcomes from eQTL mapping with those from classical QTL mapping using lignin content as a phenotypic trait, we identified a GATA transcription factor that is highly associated with lignin content. Because this GATA transcription factor was not previously known to regulate secondary cell wall biosynthesis, we evaluated its functionality by using the Populus protoplast transient expression assays to determine its subcellular localization and transcriptional activity. Furthermore, we generated Populus overexpression transgenic plants and CRISPR-knockout lines to examine their phenotypic effects on secondary cell wall biosynthesis. Through transcriptomics analysis, we found that the expression of many genes associated with secondary cell wall biosynthesis were altered in the transgenic lines, supporting a role of GATA transcription factor in regulating secondary cell wall biosynthesis. Taken together, these findings have identified new regulators and provided new insights into the complex transcriptional regulation of secondary cell wall biosynthesis in Populus.