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Rhododendron spp. is an important ornamental species that is widely cultivated for landscape worldwide. Heat stress is a major obstacle for its cultivation in south China. Previous studies on rhododendron principally focused on its physiological and biochemical processes, which are involved in a series of stress tolerance. However, molecular or genetic properties of rhododendron's response to heat stress are still poorly understood. The phenotype and chlorophyll fluorescence kinetics parameters of four rhododendron cultivars were compared under normal or heat stress conditions, and a cultivar with highest heat tolerance, "Yanzhimi" (R. obtusum) was selected for transcriptome sequencing. A total of 325,429,240 high quality reads were obtained and assembled into 395,561 transcripts and 92,463 unigenes. Functional annotation showed that 38,724 unigenes had sequence similarity to known genes in at least one of the proteins or nucleotide databases used in this study. These 38,724 unigenes were categorized into 51 functional groups based on Gene Ontology classification and were blasted to 24 known cluster of orthologous groups. A total of 973 identified unigenes belonged to 57 transcription factor families, including the stress-related HSF, DREB, ZNF, and NAC genes. Photosynthesis was significantly enriched in the Kyoto Encyclopedia of Genes and Genomes pathway, and the changed expression pattern was illustrated. The key pathways and signaling components that contribute to heat tolerance in rhododendron were revealed. These results provide a potentially valuable resource that can be used for heat-tolerance breeding.

Grape is one of the most important fruit crops worldwide. The suitable geographical locations and productivity of grapes are largely limited by temperature. Vitis amurensis is a wild grapevine species with remarkable cold-tolerance, exceeding that of Vitis vinifera, the dominant cultivated species of grapevine. However, the molecular mechanisms that contribute to the enhanced freezing tolerance of V. amurensis remain unknown. Here we used deep sequencing data from restriction endonuclease-generated cDNA fragments to evaluate the whole genome wide modification of transcriptome of V. amurensis under cold treatment. Vitis vinifera cv. Muscat of Hamburg was used as control to help investigate the distinctive features of V. amruensis in responding to cold stress. Approximately 9 million tags were sequenced from non-cold treatment (NCT) and cold treatment (CT) cDNA libraries in each species of grapevine sampled from shoot apices. Alignment of tags into V. vinifera cv. Pinot noir (PN40024) annotated genome identified over 15,000 transcripts in each library in V. amruensis and more than 16,000 in Muscat of Hamburg. Comparative analysis between NCT and CT libraries indicate that V. amurensis has fewer differential expressed genes (DEGs, 1314 transcripts) than Muscat of Hamburg (2307 transcripts) when exposed to cold stress. Common DEGs (408 transcripts) suggest that some genes provide fundamental roles during cold stress in grapes. The most robust DEGs (more than 20-fold change) also demonstrated significant differences between two kinds of grapevine, indicating that cold stress may trigger species specific pathways in V. amurensis. Functional categories of DEGs indicated that the proportion of up-regulated transcripts related to metabolism, transport, signal transduction and transcription were more abundant in V. amurensis. Several highly expressed transcripts that were found uniquely accumulated in V. amurensis are discussed in detail. This subset of unique candidate transcripts may contribute to the excellent cold-hardiness of V. amurensis.