BackgroundPremature leaf senescence induced by external stress conditions, e.g. drought stress, is a main factor for yield losses in barley. Research in drought stress tolerance has become more important as due to climate change the number of drought periods will increase and tolerance to drought stress has become a goal of high interest in barley breeding. Therefore, the aim is to identify quantitative trait loci (QTL) involved in drought stress induced leaf senescence and drought stress tolerance in early developmental stages of barley (Hordeum vulgare L.) by applying genome wide association studies (GWAS) on a set of 156 winter barley genotypes.ResultsAfter a four weeks stress period (BBCH 33) leaf colour as an indicator of leaf senescence, electron transport rate at photosystem II, content of free proline, content of soluble sugars, osmolality and the aboveground biomass indicative for drought stress response were determined in the control and stress variant in greenhouse pot experiments. Significant phenotypic variation was observed for all traits analysed. Heritabilities ranged between 0.27 for osmolality and 0.61 for leaf colour in stress treatment and significant effects of genotype, treatment and genotype x treatment were estimated for most traits analysed. Based on these phenotypic data and 3,212 polymorphic single nucleotide polymorphisms (SNP) with a minor allele frequency >5 % derived from the Illumina 9 k iSelect SNP Chip, 181 QTL were detected for all traits analysed. Major QTLs for drought stress and leaf senescence were located on chromosome 5H and 2H. BlastX search for associated marker sequences revealed that respective SNPs are in some cases located in proteins related to drought stress or leaf senescence, e.g. nucleotide pyrophosphatase (AVP1) or serine/ threonin protein kinase (SAPK9).ConclusionsGWAS resulted in the identification of many QTLs involved in drought stress and leaf senescence of which two major QTLs for drought stress and leaf senescence were located on chromosome 5H and 2H. Results may be the basis to incorporate breeding for tolerance to drought stress or leaf senescence in barley breeding via marker based selection procedures.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0524-3) contains supplementary material, which is available to authorized users.

Changes in the function and composition of the photosynthetic apparatus were analysed during maturation and senescence of barley (Hordeum vulgare L.) flag leaves under field conditions. At about 8 d post‐antbesis. photo‐synthetic capacity, measured as oxygen evolution under light‐saturating conditions, and the D1 protein level started to decrease. At about 14 d post‐anthesis, the pigment content, photosystem II efficiency (Fv/Fm) and levels of cytochrome f and the large subunit of ribulose‐1,5‐bis‐phosphate carboxylase started to decline. The levels of cytochrome b559 and the small subunit of ribulose‐1,5‐bis‐phosphate carboxylase decreased later, at about 22 d post‐anthesis. High levels of the light‐harvesting complex of pliotosyslem II were still detectable at an even later stage of senescence, at 26 d post‐anthesis. There were also differences in the kinetics of the declines in the levels of transcripts coding for components of the photosynthetic apparatus. rbcS mKNA abundance had already decreased when flag leaves reached their final lengths, at about 4 d post‐unthesis, whereas levels of psbA and petC transcripts did not decrease until 16 d post‐anthesis. In contrast, a senescence‐related transcript, pHvS40 (Becker & Apel 1993), accumulated in the flag leaves 14 d post‐anthesis. Several senescence‐related processes which differ in their kinetics are described. The interrelationships among these processes and their regulation are discussed.

HIPP26 from Arabidopsis thaliana belongs to a novel class of plant proteins, characterized by a heavy metal associated domain and an additional isoprenylation motif. It is induced during cold, salt and drought stress. The nuclear localization of HIPP26, predicted by a NLS motif, could be confirmed in onion epidermal cells overexpressing GFP-HIPP26. Experiments with modified HIPP26 indicate that the isoprenylation plays a role in the spatial distribution in the nucleus. Using promoter-GUS constructs, a tissue specific expression pattern of HIPP26 could be shown, with high expression in the vascular tissue. By a yeast-two-hybrid approach a strong interaction of HIPP26 with the zinc finger homeodomain transcription factor ATHB29, which is known to play a role in dehydration stress response could be detected. This was confirmed by GST pull-down assays. When using a modified HIPP26 lacking the two central cysteines of the heavy metal associated domain, ATHB29 was not bound in the GST pull-down assay, indicating that this structure is necessary for the interaction. Further yeast-two-hybrid analyses testing interaction of different members of the HIPP family with related zinc finger transcription factors revealed a specific interaction of ATHB29 with several HIPP proteins. A functional relationship between HIPP26 and ATHB29 is also indicated by experiments with mutants of HIPP26 showing altered expression levels of such genes known to be regulated by ATHB29.

HighlightOsmotic stress enhances the rate of protein glycation and monosaccharide autoxidation is the main pathway.

Leaf senescence, the final step of leaf development, involves extensive reprogramming of gene expression. Here, we show that these processes include discrete changes of epigenetic indexing, as well as global alterations in chromatin organization. During leaf senescence, the interphase nuclei show a decondensation of chromocenter heterochromatin, and changes in the nuclear distribution of the H3K4me2, H3K4me3, and the H3K27me2 and H3K27me3 histone modification marks that index active and inactive chromatin, respectively. Locus-specific epigenetic indexing was studied at the WRKY53 key regulator of leaf senescence. During senescence, when the locus becomes activated, H3K4me2 and H3K4me3 are significantly increased at the 5¢ end and at coding regions. Impairment of these processes is observed in plants overexpressing the SUVH2 histone methyltransferase, which causes ectopic heterochromatization. In these plants the transcriptional initiation of WRKY53 and of the senescence-associated genes SIRK, SAG101, ANAC083, SAG12 and SAG24 is inhibited, resulting in a delay of leaf senescence. In SUVH2 overexpression plants, significant levels of H3K27me2 and H3K27me3 are detected at the 5¢-end region of WRKY53, resulting in its transcriptional repression. Furthermore, SUVH2 overexpression inhibits senescence-associated global changes in chromatin organization. Our data suggest that complex epigenetic processes control the senescence-specific gene expression pattern.