**1. Introduction**

The protein kinases (PKs) and protein phosphatases (PPs) are known to regulate the protein function, and are the fundamental molecular mechanism, by reversing protein phosphorylation during cellular signaling. Thus, it is involved in many biological processes, such as signal transduction, development, and environmental stimuli [1]. The PKs phosphorylate largely serine (Ser), threonine (Thr), and tyrosine (Tyr), whereas PPs can reverse this functioning by eliminating the phosphate group [2]. Mainly, the PPs are subcategorized into three major groups based on their requirement

for substrate specificity, namely Ser/Thr phosphatases (STPs), protein Tyr phosphatases (PTPs), and dual-specificity phosphatases (DSPTPs) [3,4]. Moreover, based on crystalline structure, amino acid sequence and compassion to specific inhibitors (okadaic acid and cyclosporine-A), the PTPs are further classified into phosphoprotein metallophosphatase (PPM) and phosphoprotein phosphatases (PPP) [5]. The PPM family mainly involves Mn2+- or Mg2+-dependent protein phosphatase (PP2C) and pyruvate dehydrogenase phosphate, however, the PPP family includes different types of protein phosphatase, including PP1, PP4, PP5, PP6, PP7, PP2A, and PP2B [5]. In the PPP family, PP2A rigorously affects root hair growth during the elongation phase by denaturing the shape of the cells [6].

PP2C are evolutionarily conserved from Archaea to higher plants that pointedly modulate stress signaling pathways and reverse the stress-induced PK cascades to complex environmental stimuli [3]. From various literature, several key stress-responsive protein kinases genes have been extensively studied and proven to respond in diverse stress conditions including biotic and abiotic factors [7,8]. In *Arabidopsis*, several members of PP2c such as PLL4 and PLL5 (POL-like gene) are known to adjust leaf development, though with no obvious functions within the meristem [9].

In *Arabidopsis* and rice, 112 and 132, respectively, candidate *PP2C* genes have been characterized into various groups [10,11]. In particular, group A of *Arabidopsis* PP2Cs (e.g., ABI1 and ABI2), is accompanied by abscisic acid (ABA) signaling, group B is known to stimulate mitogen-activated protein kinase (MAPK) signaling, and group C is involved in the regulation of flower development [12]. Moreover, several members of PP2C have been implicated as a negative regulator in mediated stress signaling within ABA [13–15]. In higher plants, PP2Cs act as negative regulators of the ABA signaling pathway and reduce tolerance against oxidative stress [16]. Proteins encoded by these candidate genes play a critical role in various abiotic stress signaling such as salt, drought, and freezing [17–20]. Crop productivity encounters a number of abiotic stress signaling including salt, drought, heat, and osmotic stress in the environment. Thus, plants have developed complex molecular mechanisms to implement and survive during adverse growth conditions. Intriguingly, it can be contingent on quite a few factors, like adaptive alterations in their structure, physiology, and gene expression of some regulatory proteins [16]. In reaction to drought stress, the interaction of PP2C i.e., MPK3 and MPK6, assists plants in stomatal assimilation to thwart water loss [21], such as in the *Arabidopsis* [22]. Taken together, the above studies have established the diverse role of *PP2C* genes in plant development and environmental stresses. Hence, it is indispensable to probe into the identification and functional description of the *PP2C* gene family, which will cement the base for understanding its essential molecular mechanism in stress signaling.

Cotton, as an oil crop and an important source of natural textile fiber, plays a crucial role in agriculture and industry all around the world. However, its production is mainly constrained due to various abiotic and biotic stress conditions. The release of *Gossypium* whole-genome data in four different cotton species, such as *Gossypium arboreum* [2], *Gossypium barbadense* [23], *Gossypium hirsutum* [24], and *Gossypium raimondii* [25] and their publicly available database allows us to comprehensively characterize the *PP2C* gene family based on bioinformatic tools. We further compared the *PP2C* genes between *Gossypium* and *Arabidopsis*, to explore and identify both shared and specific subgroups. Following the gene structure organization analysis, conserved protein motifs, and cis-elements, we traced the duplication gene pairs and their evolutionary divergence that likely resulted in the widespread extension of the *PP2C* gene family. In order to shed light on some critical *PP2C* genes, their associated indigenous functional roles were further exposed to heat, cold, drought, and salt stress conditions. Additionally, the transcriptional profiling of the *PP2C* genes for various tissues and fiber development and qRT-PCR analysis of 30 genes were analyzed and compared. Therefore, to our knowledge, this is the first systematic report of the genome-wide expression dynamics of the *PP2C* genes in cotton species, and it is necessary to carry out a comprehensive study to understand the regulation of phosphatases in cotton during stress and development.
