Transcriptome Profiling of Citrus Macrophylla Bark Tissues Under Drought Stress

Citrus macrophylla Wester (CM) has valuable agronomic characteristics such as the ability to grow in saline soils, although with low tolerance to prolonged drought stress (DS) . To understand the mechanisms that characterize CM response to water scarcity, this study compared transcriptome profile changes in CM stem tissue when exposed to DS and identified a total of 2,745 differentially expressed transcripts (DETs, fold change >2), of which 631 were up-regulated and 2,114 were down-regulated. Negatively regulated transcripts were mainly assigned to photosynthesis, transport, phenylpropanoids, calcium dependent kinases, brassinosteroids and other hormones including salicylic acid and abscisic acid. DETs up-regulated by DS were enriched in pathways such as the redox and osmotic system or soluble carbohydrates and in transcripts for low molecular weight proteins such as late embryogenesis abundant protein (LEA). In the environment citrus plants face both abiotic and biotic stresses and to assess the interplay of DS and Citrus tristeza virus (CTV) infection, twelve genes were profiled by quantitative PCR (qPCR) analysis in control and CTV-infected CM plants, with or without DS. The twelve analyzed transcripts were significantly correlated (r = 0.82, p < 0.001) with the RNA-Seq results and gave insight into the response of CM to drought and/or to infection with CTV . Transcriptome results unveiled highly responsive genes to DS in stem tissue, which may be candidates for genetic selection of high drought tolerant plants of CM