Genetic Dissection of Gene Expression Variation of Secondary Cell Wall Related Transcription Factors in Eucalyptus Hybrid Populations

Secondary cell wall (SCW) deposition is a carbon sink in woody plants and an irreversible developmental commitment ending in programmed cell death. The biosynthetic processes involved in fibre SCW wall formation are guided by intrinsic developmental programmes and extrinsic signals such as mechanical stress in woody stems and are tightly co-ordinated. SCW formation is transcriptionally regulated by a complex network of transcription factors, many of which have been studied in the model plants Arabidopsis and Populus. It is not currently known how natural variation in gene expression of SCW related transcription factors might affect cell wall deposition and wood properties. The aim of this study is to elucidate the genetic architecture of gene expression variation of SCW-related transcription factors in Eucalyptus hybrid populations. Illumina RNA-Seq expression profiling (30 million PE50 reads) of immature xylem from 280 F2 backcross progeny of an E. grandis x E. urophylla hybrid were used to perform expression QTL (eQTL) mapping and expression correlation analyses of SCW-related transcription factor homologs in the E. grandis genome. We found that many SCW related transcription factor genes shared trans-acting eQTLs, possibly relating to polymorphisms affecting shared upstream transcription factors in the SCW transcriptional network. Using information from expression correlation across 280 individuals and shared eQTLs, we aim to reconstruct regulatory modules of the Eucalyptus SCW transcriptional network and identify novel candidate transcription factors for further studies of the transcriptional control of SCW deposition.