Genomic Analysis of Wood Production in Sunflower.

Silver-leaf sunflower (Helianthus argophyllus) is a wood-forming annual plant.  Our objective was to study the structure and genetic regulation of secondary xylem production in silver-leaf sunflower. Anatomical images of silver-leaf sunflower stems show vascular cambium divisions beginning in 4-6 week old seedlings.  Pyrolysis coupled mass spectrometry (MS) was used to determine cell wall chemistry of silver-leaf sunflowers and cultivated sunflowers (H. annuus, non-woody stems).  Wet-chemistry and MS quantification of lignin and C5 sugars will be presented.  Data for genomic analysis of wood formation were obtained by transcriptome sequencing of developing stems.  Non-normalized cDNA libraries were constructed using mRNA isolated from stems of H. annuus and H. argophyllus and sequenced on a 454-FLX Titanium platform.  The sequences were processed through a bioinformatic pipeline and assembled using CAP3.  A BLAST search of new ESTs with the existing sunflower database identified 15,595 H. argophyllus and 12,260 H. annuus novel ESTs.  An updated transcript assembly consisting of 144,442 H. annuus and 50,776 H. argophyllus ESTs was used to build a custom gene expression microarray.  Results from time course experiments designed to study developmentally specific, differentially expressed genes will be presented.  Genomic regions involved in wood development and other biomass traits will be identified by QTL mapping in a backcross (BC1) population developed from a hybrid of non-woody H. annuus NMS377 (PI 560145) x woody H. argophyllus 1820 (PI 494580).  The BC1 population was phenotyped for agronomic and biomass traits during summer 2009 in Georgia and Iowa (US) and British Columbia (Canada) and will be genotyped with a 384-SNP array (BeadXpress).  SNPs on the BeadXpress array were selected based on BC1 parental SNP polymorphisms identified with a 10,640 Infinium SNP array.