![srdx as a suppressor for transcription factors srdx as a suppressor for transcription factors](https://www.ahajournals.org/cms/asset/99c9fad9-d66e-4ec3-9820-19c0c43a3939/g10ff2.jpg)
Specifically, type A PP2Cs, such as ABI1, ABI2 and AtPP2CA, have been well characterized as negative regulators of ABA signaling. In Arabidopsis, 76 PP2Cs have been identified to date, and these function in signal transduction pathways for stress responses and development. Type 2C serine/threonine protein phosphatases (PP2Cs) constitute the largest protein phosphatase family in various plant genomes and are known to play important roles in eukaryotic signal transduction.
![srdx as a suppressor for transcription factors srdx as a suppressor for transcription factors](http://www.cs.uni.edu/~fienup/cs188s05/lectures/eukaryotic_gene_regulation.gif)
For example, the Arabidopsis thaliana (At) MYB2 (AtMYB2) interacts with calmodulin and enhances salt stress tolerance, overexpression of AtMYB44 results in rapid abscisic acid (ABA)-induced stomatal closure and enhances abiotic stress tolerance and MYB15 enhances the expressions of genes involved in ABA biosynthesis and improves salt and drought tolerance. In Arabidopsis, more than 100 MYBs have been identified as R2R3-MYB proteins, and many of these are known to be involved in the transcriptional regulation of a variety of biological processes related to growth and development, as well as responses to biotic and abiotic stresses. The MYB family of TFs is very large and has been subdivided into four different subgroups based on sequence similarities of the MYB domain: 1R-, R2R3-, 3R-, and 4R-MYB. These proteins have been classified into different super families, such as the MYB, bZIP, WRKY, ZINK and ERF. Studies on plant genomes have identified a large number of transcription factors (TFs) that regulate gene transcription through their direct or indirect binding to DNA. In plant stress adaptation processes, the transcriptional regulation of gene expression is a critical step in establishing the cellular stress physiology that will enable the plant to survive and sustain. Plants possess molecular and cellular mechanisms to sense environmental stresses and to transduce stress signals and activate stress-responsive gene expression, all of which ultimately enable the plant to make the appropriate physiological and biochemical adaptations to the stress. Salinity is one of the more severe environmental factors that limits plant biomass-based crop production, primarily by reducing seed germination, root elongation and growth. Plants are sessile organisms and therefore cannot ‘escape’ by moving away from adverse living conditions arising from environmental perturbations.