Abstracts Category : Other

Geneticarchitecture of transcription factor expression variation indeveloping secondary xylem of Eucalyptus grandis x E.urophylla

by Megan Calvert

The xylem secondary cell walls (SCW) are a strongcarbon sink in woody plants and part of an irreversibledevelopmental commitment which ends in programmed cell death. Thebiosynthetic processes involved in fibre SCW wall formation areguided by intrinsic developmental programmes and extrinsic signals,such as mechanical stress in woody stems, which are tightlyco-ordinated. The model plants Arabidopsis and Populus have beenused to study many of the transcription factors which are involvedin the complex network responsible for the regulation of theformation of SCW. It is thought that variation in the expression ofSCW transcription factor genes will affect cell wall depositionand wood properties in commercially important wood fibre cropssuch as Eucalyptus tree species and hybrids. To date thetranscriptional control of SCW deposition in woody plants has notbeen fully resolved nor is it known which components of thetranscriptional network regulating SCW exhibit natural variationin expression, or what the genetic architecture of such regulatoryvariation might be. In this study expression quantitative traitlocus (eQTL) mapping and expression correlation analyses wasperformed for SCW-related transcription factor (transcriptionfactor) homologs predicted in the Eucalyptus grandis genome. Theexpression of 353 candidate xylem-expressed transcription factorgenes was quantified in the immature xylem of 156 and 127 F2backcross progeny of an E. grandis x E. urophylla F1 hybridrespectively using Illumina RNA-Seq expression profiling. Many ofthe SCW related transcription factor genes shared trans-actingeQTLs or had shared cis- and trans-eQTLs, indicating the presenceof polymorphisms affecting the expression of these SCWtranscription factors and their downstream targets in thetranscriptional network. Using information from expressioncorrelation across 283 individuals and from shared transcriptionfactor eQTLs, regulatory modules of the Eucalyptus SCWtranscriptional network were partially reconstructed allowing theidentification of known and novel candidate transcription factorgenes and their genetic interactions that represent novel targetsfor functional studies in woody plants.Advisors/Committee Members: Myburg, Alexander Andrew (advisor), Mizrachi, Eshchar (coadvisor), Christie, Nanette (coadvisor).