No abstract

Elettaria cardamomum (L.) Maton, known as ‘queen of spices, is a perennial herbaceous monocot of the family Zingiberaceae, native to southern India. Cardamom is an economically valuable spice crop and used widely in culinary and medicinal purposes. In the present study, using Ion Proton RNA sequencing technology, we performed transcriptome sequencing and de novo transcriptome assembly of a wild and five cultivar genotypes of cardamom. RNA-seq generated a total of 22,811,983 (92 base) and 24,889,197 (75 base) raw reads accounting for approximately 8.21GB and 7.65GB of sequence data for wild and cultivar genotypes of cardamom respectively. The raw data were submitted to SRA database of NCBI under the accession numbers SRX1141272 (wild) and SRX1141276 (cultivars). The raw reads were quality filtered and assembled using MIRA assembler resulted with 112,208 and 264,161contigs having N50 value 616 and 664 for wild and cultivar cardamom respectively. The assembled unigenes were functionally annotated using several databases including PlantCyc for pathway annotation. This work represents the first report on cardamom transcriptome sequencing. In order to generate a comprehensive reference transcriptome, we further assembled the raw reads of wild and cultivar genotypes which might enrich the plant transcriptome database and trigger advanced research in cardamom genomics.

MicroRNAs (miRNAs) are endogenous, 19-24-nucleotide-long, noncoding RNAs found in animals, plants, and some viruses. Drought is one of the major limiting factors that negatively affect productivity of plants. To date, nothing is known about the regulatory roles of miRNAs in response to drought stress in cardamom. Cardamom collected from the natural forest area in Therakkudi in the Idamalayar forest range was selected for the study. Total RNA was isolated from leaves and stems of control and drought treated cardamom plant, which was used for library construction. Ion torrent sequencing of the two small RNA libraries prepared from plants raised under well irrigated and drought stressed treatments, respectively, created 3,938,342 and 4,083,181 primary reads. A total of 150 conserved and 20 novel microRNAs were identified from both the control and the treated libraries. Discovery of 17 differentially expressed miRNAs under drought stress suggests that these might have been involved in various biological processes to improve plant tolerance to water stress. This study is the first report of drought responsive miRNAs and their targets in cardamom. The outcome of this research could provide insights into the miRNA based regulatory mechanisms in response to drought stress in monocot plants.

Elettaria cardamomum (L.) Maton, or small cardamom referred as ‘queen of spices’, is a perennial herbaceous rhizomatous monocot of the family Zingiberaceae. Cardamom seeds and fruits are the economically significant parts and effectively used as a traditional medicine, food additive and flavoring agent. In the present study, using Ion Proton next generation sequencing technology we performed the small RNA sequencing, conserved and novel miRNA predictions of a wild and five cultivar genotypes of cardamom. Small RNA sequencing generated a total of 5,451,328 and 2,756,250 raw reads for wild and cultivar cardamom respectively. The raw data was submitted to SRA database of NCBI under the accession numbers and SRX2273863 (wild) and SRX2273862 (cultivars). The raw reads were quality filtered and predicted conserved and novel miRNAs for wild and cultivar cardamom. The predicted miRNAs, miRNA-targets and functional annotations might provide valuable insights into differences between wild progenitor and cultivated cardamom.

Cardamom has long been used as a food flavouring agent and in ayurvedic medicines for mouth ulcers, digestive problems and even depression. Extensive occurrence of pests and diseases adversely affect its cultivation and result in substantial reductions in total production and productivity. Numerous studies revealed the significant role of miRNAs in plant biotic stress responses. In the current study, miRNA profiling of cultivar and wild cardamom genotypes was performed using an Ion Proton sequencer. We identified 161 potential miRNAs representing 42 families, including monocot/tissue-specific and 14 novel miRNAs in both genotypes. Significant differences in miRNA family abundance between the libraries were observed in read frequencies. A total of 19 miRNAs (from known miRNAs) displayed a twofold difference in expression between wild and cultivar genotypes. We found 1168 unique potential targets for 40 known miRNA families in wild and 1025 potential targets for 42 known miRNA families in cultivar genotypes. The differential expression analysis revealed that most miRNAs identified were highly expressed in cultivars and, furthermore, lower expression of miR169 and higher expression of miR529 in wild cardamom proved evidence that wild genotypes have stronger drought stress tolerance and floral development than cultivars. Potential targets predicted for the newly identified miRNAs from the miRNA libraries of wild and cultivar cardamom genotypes involved in metabolic and developmental processes and in response to various stimuli. qRT-PCR confirmed miRNAs were differentially expressed between wild and cultivar genotypes. Furthermore, four target genes were validated experimentally to confirm miRNA-mRNA target pairing using RNA ligase-mediated 5' Rapid Amplification of cDNA Ends (5'RLM-RACE) PCR.