not-yet-known not-yet-known not-yet-known unknown 1 Introduction Since the 20th century, droughts in arid and semi-arid regions have been occurring more frequently and extensively as a result of global climate change (Mukarram et al., 2021). In the natural environment, terrestrial plants can change their morphology, structure, physiological and biochemical characteristics and even the level of genetic material in response to changes of ecological factors, increasingly molding their adaptation and response mechanisms by long natural selection (Mcintyre et al., 1999). In other words, the drought adaptation and response mechanisms of plants show great variance and diversity among or within species (de Dorlodot et al., 2007), however, they are influenced by both genetic differentiation (local adaptation) and environmental modification (phenotypic plasticity) and are related to seed sources (Klein & Mitchell, 2024). Therefore, exploring how individuals from different regions of a key plant species adapt and respond to drought and estimating their differences and diversity are essential to understanding and predicting population evolution potential and distribution region shift. Plant growth, morphology, physiological and behavior traits and DNA-based molecular methods have been proven powerful to explore the differences in drought adaptation and response mechanisms among populations or regions of a species (Pacini & Dolferus, 2019; Qian et al., 2021; Seiler & Cazell, 1990; Wang et al., 2006a). However, these methods are limited to explain how they regulate plant physiological functioning. In the past years, RNA-seq technology has been widely used to study how different samples within a species regulate plant physiological functioning to adapt and respond to environmental stresses in the absence of information of the whole genome sequence (Jin et al., 2013; Villarino et al., 2014; Zou et al., 2022). For RNA-Seq data of the plant samples from different environmental treatments, differentially expressed genes (DEGs) between treatments could be found and used for KEGG functional enrichment and / or annotation analysis to explore how they regulate the response processes in the face of environmental changes. Consequently, the response processes of DEGs across treatments could be compared between or among different samples. For example, Nawae et al. (2020) have analyzed the DEGs between two water conditions for two genotypes of sugarcane, KPS01-12 (drought-tolerant genotype) and UT12 (drought-sensitive genotype), and found that it is KPS01-12 but not UT12 that up-regulates expression of genes related to drought-tolerance such as water retention and antioxidant secondary metabolite biosynthesis. Precipitation pattern changes and an increase in the frequency of extreme droughts in globally sensitive regions have resulted in increased habitat patches and shifts of the distribution region of some species (Abreha et al., 2022), which have caused significant population differences owing to genetic drift and reduced gene flow. Therefore, in order to better understand and predict community dynamics and species distribution area fluctuations, more researches are needed to use RNA-Seq to analyze the drought adaptation and response mechanisms of the dominant species in these sensitive important regions (Ma et al., 2018). As an important part of the arid and semi-arid Eurasian Steppe, climatic characteristics of the Inner Mongolia Steppe show the decreasing precipitation and the increasing annual mean temperature from northeast to southwest, which provides an ideal area for studying drought adaptive differences of a certain species by sampling from different regions in the sensitive region. Stipa krylovii is one of the important dominant species in the Inner Mongolia Steppe, its morphological and physiological traits and trait responses show significant differences among populations / regions caused by genetic differentiation and environmental modification (Gu et al., 2015; Wang et al., 2006a; Zhao et al., 2016). To our knowledge, no study has explored the difference of adaptation strategies and the diversity of response processes to drought among different S. krylovii regions from the aspect of RNA-seq transcriptome. The gaps of knowledge would limit us to further understand the drought adaptation difference and response mechanisms diversity of S. krylovii as well as population evolution and its distribution region changes. In the present study, seedlings of S. krylovii from three regions (eastern, middle and western regions; 3 populations per region) were used as plant materials, and a seed source of region (eastern, middle and western regions) × soil moisture treatment (control, light drought and heavy drought treatments) two-factor experiment was carried out under the controlled conditions, to explore the performance of S. krylovii under each treatment in the aspect of growth (number of tillers, plant height, aboveground biomass and belowground biomass) and physiological (net photosynthetic rate, transpiration rate and stomatal conductance) traits and RNA-seq-based transcriptome. Meanwhile, gene expressions and differentially expressed genes (DEGs) between soil moisture treatments vs control for S. krylovii from each region were analyzed by KEGG functional enrichment analysis. Specifically, we proposed the drought adaptation and response mechanisms of S. krylovii were dependent on its seed source of regions, and such strategies of individuals from the eastern and middle regions were relatively similar and were different from the western region, considering that the distribution regions of S. krylovii increased in the past decades and the western part of the distribution area is more arid and unfertile than the central and eastern parts (Liu, 2004).