Characterizing the Effects of Down-regulating the GPC Genes on the Wheat Transcriptome During Monocarpic Senescence in Wheat

The nutritional content of monocarpic cereals such as wheat is dependent to a large extent on the remobilization of nitrogen and micronutrients derived from senescing leaves. In wheat, down-regulation by RNAi of the NAC transcription factor GPC-1 results in a significant delay in senescence and reduces grain protein and nutrient content, confirming the connection between senescence and nutrient translocation. However, the gene networks regulating these processes are complex and the precise mechanisms controlling monocarpic senescence and the subsequent translocation of nutrients to the developing grain remain largely unknown.  To address this problem, we undertook de novo transcriptome assembly from senescing wheat leaves using 1.4M 454 reads and mapped 145M Illumina reads from wild type and GPC-RNAi plants 12 days after anthesis to identify GPC-regulated genes. After stringent statistical analysis, we identified 691 differentially regulated genes which included transporters, transcription factors and hormone-regulated genes, providing a basis for future studies aiming to decipher these pathways.  We are currently undertaking an expanded RNA-seq experiment using TILLING mutants carrying truncations in both GPC-1 and its paralog GPC-2. Samples were taken at three stages of senescence, enabling us to monitor both the changing expression profiles of genes regulated during the onset and progression of senescence as well as the relative contribution of each GPC gene. This will provide a comprehensive analysis of the transcriptional changes induced by GPC during senescence and offer entry points to dissect both senescence and nutrient translocation pathways.