Genome-Wide Identification and Expression Analysis of Heat Shock Protein 20 (HSP20) Gene Family in Response to High-Temperature Stress in Chickpeas (<i>Cicer arietinum</i> L.)

Chickpeas (<i>Cicer arietinum</i> L.) are an important legume crop known for their rich nutrient content, including proteins, carbohydrates, and minerals. Thus, they are enjoyed by people worldwide. In recent years, the production scale of chickpeas has been growing gradually. The planting area of chickpeas represents roughly 35–36% of the total planting area, and the output of the beans is roughly 47–48%. However, the growth and development process of chickpeas is limited by a number of factors, including high temperature, drought, salt stress, and so forth. In particular, high temperatures can reduce the germination rate, photosynthesis, seed setting rate, and filling rate of chickpeas, restricting seed germination, plant growth, and reproductive growth. These changes lead to a decrease in the yield and quality of the crop. Heat shock proteins (HSPs) are small proteins that play an important role in plant defense against abiotic stress. Therefore, in the present study, HSP20 gene family members were identified based on the whole-genome data of chickpeas, and their chromosomal positions, evolutionary relationships, promoter cis-acting elements, and tissue-specific expression patterns were predicted. Subsequently, qRT-PCR was used to detect and analyze the expression characteristics of HSP20 genes under different temperature stress conditions. Ultimately, we identified twenty-one HSP20 genes distributed on seven chromosomes, and their gene family members were found to be relatively conserved, belonging to ten subfamilies. We also found that CaHSP20 promoter regions have many cis-acting elements related to growth and development, hormones, and stress responses. In addition, under high-temperature stress, the relative expression of <i>CaHSP20-17</i>, <i>CaHSP20-20</i>, <i>CaHSP20-7</i>, <i>CaHSP20-3</i>, and <i>CaHSP20-12</i> increased hundreds or even thousands of times as the temperature increased from 25 °C to 42 °C. Among them, excluding <i>CaHSP20-5</i>, the other five genes all contain 1-2 ABA cis-regulatory elements. This finding indicates that CaHSP20s are involved in the growth and development of chickpeas under heat stress, and the mechanisms of their responses to high-temperature stress may be related to hormone regulation. The results of the present study lay the foundation for exploring HSP20 gene family resources and the molecular mechanisms of heat resistance in chickpeas. Our results can also provide a theoretical basis for breeding high-temperature-resistant chickpea varieties and provide valuable information for the sustainable development of the global chickpea industry.