V o l u m e 8 0 | I s s u e 1 | F e b r u a r y 2 0 1 5 39 Europ. J. Hort. Sci. 80 (1) 39–46 | ISSN 1611-4426 print and 1611-4434 online | © ISHS 2015 The effects of drought stress on leaf gene expression during flowering in blackcurrant ( Ribes nigrum L.) N. Čereković 1 , D. Jarret 2 , M. Pagter 4,1 , D.W. Cullen 3 , J.M. Morris 3 , P.E. Hedley 3 , R. Brennan 3 and K.K. Petersen 1 1 Department of Food Science, Aarhus University, Denmark 2 Mylnefield Research Services Ltd., Invergowrie, Dundee, Scotland, UK 3 The James Hutton Institute, Invergowrie, Dundee, Scotland, UK 4 Max Planck Institute of Molecular Plant Physiology, Potsdam-Golm, Germany Original article Significance of this study What is already known on this subject? • Drought is a major limitation for crop productivity worldwide and in future periods of water stress are more likely to occur. Molecular responses to drought stress are very complex, but our understanding has rapidly progressed with the identification of thou- sands of genes involved in acclimatization and adap- tation. What are the new findings? • Genome expression analyses from blackcurrant ‘Ben Gairn’ after five days of drought stress. Volcano filtering identified 2,115 differentially expressed microarray probes; 429 were up-regulated, with 263 showing homology to unique Arabidopsis thaliana (At) accessions, and 1,686 were down-regulated, with 675 unique At numbers. What is the expected impact on horticulture? • Putative candidate genes involved in drought stress tolerance of blackcurrant were identified, but require further, more detailed, studies to confirm their role. The results provide relevant information for focusing future studies with the aim to develop drought toler- ant cultivars for sustainable production. Summary This study provides genome expression analyses from the blackcurrant cultivar ‘Ben Gairn’ after five days of drought stress. RNA Sequencing (RNA-Seq) data was utilized to generate a non-redundant set of 40,225 predicted transcripts used to design a cus- tom Ribes microarray. A set of 2,115 differentially expressed genes were identified during drought treatment; 429 of these genes were up-regulated, with 263 showing homology to unique Arabidop- sis thaliana (At) accessions, and 1,686 genes were down-regulated, with 675 unique At numbers. The Arabidopsis homologs were analysed for enrichment of GO (gene ontology) terms using the Term Enrich- ment Tool. This showed a number of GO terms highly enriched in the drought up-regulated and down-reg- ulated gene lists in GO categories associated with molecular function, biological process and cellular component. The identification of several hormone metabolism, cell wall, cell cycle, and transcription factor genes indicated that they could play an impor- tant role in the drought stress tolerance response. The results provide relevant information for focus- ing future studies with the aim to develop drought tolerant cultivars for sustainable production. Keywords cell wall and cell cycle, GO term enrichment analyses, hormone metabolism genes, Ribes microarray, tran- scription factors Introduction Blackcurrant (Ribes nigrum L.) is a woody fruit shrub grown mostly in temperate climates for juice processing, as the berries have a very high nutritional value in terms of antioxidants (Brennan and Graham, 2009). During recent growing seasons, more extreme weather conditions have had a negative impact on the productivity and sustainabili- ty of the crop in the North Sea Region. For example, extend- ed periods of droughts, as in 2013, or heavy rainfall during the production season, as in 2012, and lack of winter chill during several recent winters (Kahu et al., 2009; Anon., 2013) threaten the production of blackcurrants. Drought conditions are one of the main limiting fac- tors for crop productivity that may result in reduced yields (Hsiao, 1973; Blum, 2011). The response of plants to wa- ter deficit varies with genotypes and usually involves a mixture of tolerance and stress avoidance mechanisms (Chaves et al., 2003). The majority of studies on the molec- ular responses to drought stress were previously carried out using the model plant Arabidopsis thaliana, and many genes were characterized (Huang et al., 2008). Recently, genome and transcriptome sequence information of oth- er, non-model plant species have become available, which has led to research on the molecular responses to drought stress in perennial plants such as Populus simonii (Chen et al., 2013), Malus domestica (Wisniewski et al., 2008), and Citrus reticulata (Gimeno et al., 2009). However, the specif- ic functions of many genes remain unknown in perennial species due to inconsistency of both experimental growth conditions and species-specific genomic resources. There- fore, it is now imperative to understand the mechanism of specific responses to drought conditions in blackcurrant (Čereković et al., 2013, 2014). This information can subse- quently be used to select cultivars with an increased ability to respond to and recover from stressful conditions. Drought stress has a great similarity with other abi- otic stresses at a physical and molecular level (Chaves et German Society for Horticultural Science