441 25 Hallmark Attributes of Plant Transcription Factors and Potentials of WRKY , MYB and NAC in Abiotic Stresses Sami Ullah Jan, Muhammad Jamil, Muhammad Faraz Bhatti, and Alvina Gul 25.1 INTRODUCTION In the context of plant sciences, an increment or dec- rement in environmental component(s) which affect the development, growth, yield and nutritional mea- sures of plants is termed as stress. All stresses disrupt the plant's processes at the physiological, biochemical and molecular level (Munns, 2002; Ashraf and Harris, 2004). Stresses caused by living organisms, including insects and weeds, are known as biotic stresses while the stresses attained by non-living environmental factors such as chemicals (salts, metals), pH, humidity and tem- perature are referred to as abiotic stresses. Plants are immobilized and cannot escape from all the biotic as well as abiotic stresses, resultantly; plants are very susceptible to growth and yield losses (Ahuja et al., 2010; Xu et al., 2010; Aroca et al., 2012), ionic imbalances (Sun et al., 2003; Wang et al., 2012), variable biochemi- cal responses (Hasegawa et al., 2000), altered genome expression (Rasmussen et al., 2013) and reduction of vital nutritional contents of plants (Jamil et al., 2012; Jamil et al., 2013), surviving under numerous stresses. Upon the exposure, plants adapt specialized mechanisms at biochemical-, physiological- and molecular-level pro- cesses to combat these stresses (Wang et al., 1998; Yang et al., 2012; Cheng et al., 2013) whereas such adaptations acquired are facilitated through highly organized and com- plex interlinked signaling mechanisms (Nakashima et al., 2009). Plants possess about 300 genes in their genome dedicated to responding against stresses (Kültz, 2005). CONTENTS 25.1 Introduction .................................................................................................................................................. 441 25.2 Transcription Factors .................................................................................................................................... 442 25.3 Nomenclature of Transcription Factors ........................................................................................................ 442 25.4 Structure of Transcription Factors ................................................................................................................ 443 25.5 Classifcation of Transcription Factors ......................................................................................................... 443 25.5.1 Classifcation of Transcription Factors on the Basis of Activity....................................................... 444 25.5.2 Classifcation of Transcription Factors on the Basis of Structure ..................................................... 444 25.5.3 Classifcation of Transcription Factors on the Basis of Species ....................................................... 444 25.5.4 Classifcation of Transcription Factors with Specialized Purpose ................................................... 444 25.6 Study of Transcription Factor in Laboratory ................................................................................................ 444 25.7 Transcription Factors under Normal Conditions .......................................................................................... 446 25.7.1 Transcription Factor in Activation of Transcription ......................................................................... 446 25.7.2 Transcription Factor in Repression of Transcription ........................................................................ 447 25.8 Transcription Factor Regulation ................................................................................................................... 448 25.8.1 Regulation of Transcription Factors Synthesis ................................................................................. 448 25.8.1.1 Mechanisms of the Regulation of TFs ............................................................................... 448 25.9 Transcription Factors under Abiotic Stress ................................................................................................... 448 25.9.1 WRKY Transcription Factors ............................................................................................................ 448 25.9.2 MYB Transcription Factors ............................................................................................................... 450 25.9.3 NAC Transcription Factors ............................................................................................................... 451 25.10 Conclusion and Recommendations ............................................................................................................... 452 References ............................................................................................................................................................... 452 © 2019 Taylor and Francis LLC. 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