###### Abstract  
Garlic (_Allium sativuum_ L.) is one of the most important vegetable crops, and breeding drought-tolerant varieties is a vital research goal. However, the underlying molecular mechanisms in response to drought stress in garlic are still limited. In this study, garlic seedlings were subjected to 15% PEG6000 for 0, 1, 4, and 12 h, respectively, to simulate drought stress. Changes of transcriptomes as a result of drought stress in garlic leaves were determined by de novo assembly using the Illumina platform. In total, 96,712 unigenes and 11,936 differentially expressed genes (DEGs) were identified in the presence of drought conditions. Transcriptome profiling revealed that the DEGs were mainly enriched in the biosynthesis of secondary metabolites, MAPK signaling pathway, starch and sucrose metabolism, phenylpropanol biosynthesis, and plant hormone signal transduction. Genes involved in abscisic acid and calcium signaling were further investigated and discussed. Our results indicated that a coordinated interplay between abscisic acid and calcium is required for drought-induced response in garlic.  
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classified into two categories in light of their functions. The first group of stress-induced transcripts is related to cell protection and the signal transduction pathway regulation, such as reactive oxygen species-scavenging genes, hormone response, water channel proteins, photosynthesis-related proteins, and heat shock proteins [19; 20]. The latter gene group under water stress in plants consists of transcription factors and dehydration-responsive elements, which take part in further regulation of signal transduction and stress-responsive gene expression [21; 22].  
Nowadays, research regarding plant biology, biotechnology, and molecular biology requires mass data for the identification of the cellular state, physiology, and activity. Transcriptome analysis using next-generation sequencing can provide information about gene expression, alternative splicing, single nucleotide variation, and fusion gene detection in large quantities, which are extremely important in unsequenced organisms [23]. By now, transcriptome technology has been widely used in identifying water deficit-related genes in numerous plant species, and a deep understanding of the molecular mechanisms underlying water stress response has been achieved.  
Garlic (_Allium sativum_ L.), a member of the Lilliaceae family, is considered to be one of the most important vegetables worldwide with a harvested area of 834,226 ha and an annual production of 23,305,888 tonnes in China (FAO, 2019). Garlic is commonly used as a raw vegetable for culinary purposes. It is also popular in traditional and modern medicines, owing to its therapeutic and medicinal effects [24; 25]. Garlic plants usually experience water stress during the period of growth and development, leading to decreased yield and quality. Abscisic acid and calcium signaling have been demonstrated to contribute to plant response to drought stress in many plants [26; 27]. However, there is limited information about the response of garlic plants under water stress at the molecular level. Therefore, it is unknown whether abscisic acid and calcium could get involved in the process in garlic.  
Our study aimed to identify genes in polyethylene glycol 6000 (PEG6000)-simulated drought stress by the Illumina HiSeq platform. Here, we investigated (1) how gene expression varied at different treatment times with respect to the well-watered conditions and (2) the role of abscisic acid and calcium signaling pathways in garlic plants' response to water stress. The results from this study would provide genetic resources about garlic plants exposed to water deficit and contribute to breeding aimed at improving garlic resistance against water stress.