Comparative transcriptome profiling of near-isogenic barley (Hordeum vulgare) lines differing in the allelic state of a major grain protein content locus identifies genes with possible roles in leaf senescence and nitrogen reallocation.

To identify genes involved in the regulation and execution of leaf senescence and whole-plant nitrogen reallocation, near-isogenic barley germplasm divergent in senescence timing and protein concentration of mature grains was contrasted. Barley lines differing in allelic state at a major locus on chromosome six, controlling grain protein concentration, were obtained after four generations of backcrossing. Based on physiological data indicating major differences between low- and high-grain protein germplasm at 14-21 d past anthesis, the flag leaf and kernel transcriptomes of the low-protein parent and one high-protein near-isogenic line were compared at these time points, using the 22-k Barley1 Affymetrix microarray. Our data associate several genes with both known (based on sequence comparisons) and unknown functions with the senescence process. These include leucine-rich repeat transmembrane protein kinases, a glycine-rich RNA-binding protein with homology to AtGRP7 and a 'mother of FT/TF1' gene. Our data also indicate upregulation of genes coding for both plastidial and extraplastidial proteases in germplasm with accelerated leaf senescence. Functional characterization of candidate genes identified by this research may contribute to our understanding of the molecular network underlying leaf senescence and nitrogen reallocation.