Characterization of Citrus WRKY transcription factors and their responses to phytohormones and abiotic stresses

WRKY transcription factors (TF) family is involved in a huge variety of plant processes, including seed germination, plant development, phytohormone signalling, and defence against both biotic or abiotic stresses. In this work, WRKY TF family has been characterized in citrus. In a first experiment, the relative expression of CsWRKYs was analyzed in shoots and roots of plants treated with abscisic acid (ABA), salicylic acid (SA), and methyl jasmonate (MeJA) under in vitro conditions. Expression of CsWRKYs was also determined in roots of commercial citrus rootstocks subjected to osmotic and salt stresses. A total amount of 50 CsWRKYs has been found and devided into different groups of WRKY family according to the WRKY domain sequences. In response to the applications of phytohormones, the highest differences were observed in roots, and it was found that ABA and SA generally repressed CsWRKYs expressions, but MeJA induced their overexpression. Osmotic stress repressed the expression of most of the CsWRKYs, whereas salt stress induced their expression. Moreover, salt stress induced higher increase in CsWRKY expressions in the tolerant rootstock Citrus macrophylla than in the sensitive rootstock Carrizo citrange, suggesting that these TFs may play an important role in response to this stress.