Expression Characteristics and Functional Analysis of the ScWRKY3 Gene from Sugarcane

The plant-specific WRKY transcriptional regulatory factors have been proven to play vital roles in plant growth, development, and responses to biotic and abiotic stresses. However, there are few studies on the WRKY gene family in sugarcane (Saccharum spp.). In the present study, the characterization of a new subgroup, IIc WRKY protein ScWRKY3, from a Saccharum hybrid cultivar is reported. The ScWRKY3 protein was localized in the nucleus of Nicotiana benthamiana leaves and showed no transcriptional activation activity and no toxic effects on the yeast strain Y2HGold. An interaction between ScWRKY3 and a reported sugarcane protein ScWRKY4, was confirmed in the nucleus. The ScWRKY3 gene had the highest expression level in sugarcane stem pith. The transcript of ScWRKY3 was stable in the smut-resistant Saccharum hybrid cultivar Yacheng05-179, while it was down-regulated in the smut-susceptible Saccharum hybrid cultivar ROC22 during inoculation with the smut pathogen (Sporisorium scitamineum) at 0-72 h. ScWRKY3 was remarkably up-regulated by sodium chloride (NaCl), polyethylene glycol (PEG), and plant hormone abscisic acid (ABA), but it was down-regulated by salicylic acid (SA) and methyl jasmonate (MeJA). Moreover, transient overexpression of the ScWRKY3 gene in N. benthamiana indicated a negative regulation during challenges with the fungal pathogen Fusarium solani var. coeruleum or the bacterial pathogen Ralstonia solanacearum in N. benthamiana. The findings of the present study should accelerate future research on the identification and functional characterization of the WRKY family in sugarcane.