Molecular Plant Breeding 2024, Vol.15, No.2, 42-51 http://genbreedpublisher.com/index.php/mpb 43 In 1994, the first member of the WRKY transcription factors was discovered in sweet potato (Ipomoea batatas). Since then, researchers have identified numerous WRKY transcription factor members in many plants. Arabidopsis has over 100 WRKY members, each with one or two WRKY structural domains. Rice has 102 WRKY members, soybean has 197, cotton has 116, oilseed rape has 46, tomato has 81, poplar has 104, and rubber tree has 81 members. The WRKY structural domain is a sequence of 60 amino acids that includes a highly conserved amino acid sequence, WRKYGQK, at the N-terminus and a zinc finger domain. Most WRKY proteins bind to the W-box [TGAC(C/T)], which is present in the promoters of various genes related to plant defense responses. This binding helps in mediating transcriptional responses induced by pathogens. When the plant is infected with viruses, bacteria, or fungi, or treated with signaling agents like salicylic acid, mRNA and protein synthesis of WRKY transcription factors increases and enhances their DNA-binding activity (Dong et al., 2003). The W-box and WRKY transcription factors work together to regulate the expression of downstream gene products that provide protection and defense against pathogens. 2 Role of WRKY Transcription Factors in Abiotic Stresses Abiotic stresses can affect normal physiological and biochemical processes in plants. Research has shown that WRKY transcription factors play a significant role in regulating plant responses to abiotic stresses. WRKY proteins are one of the largest families of transcription factors in higher plants, and they participate in complex signaling pathways and response mechanisms. Moreover, individual WRKY proteins can regulate multiple stress responses, and they may even play a role in both biotic and abiotic stresses. WRKY transcription factors are involved in the response to abiotic stresses such as drought, high salt and temperature (Figure 1) (Wu et al., 2020). For example, transcriptome analysis showed that 41 OsWRKY genes in rice, 20 AtWRKY genes in Arabidopsis, and 74 BnWRKY genes in oilseed rape were involved in the response to abiotic stress (Ramamoorthy et al., 2008; Chen et al., 2012). Figure 1 The function of WRKY in plant abiotic stress signaling network (Adopted from Wu et al., 2020) 2.1 Drought stress Drought stress has been found to be the most detrimental abiotic stress on plant growth and development, according to studies. Drought causes stomatal closure and lowers plant water content, reducing transpiration and affecting photosynthesis and solute accumulation. The WRKY family of transcription factors is essential for plant drought tolerance.
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