Abstract
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.
Highlights
Plant growth and development are vulnerable to several external environmental challenges, such as drought, high salinity, cold, and pathogens
As one of the largest groups of transcription factors (TFs), the WRKY proteins have been found in a wide range of plant species since the initial WRKY cDNA was isolated from sweet potato [31]
Under abscisic acid (ABA) stress, the transcript of ScWRKY4 was remarkably up-regulated by 1.59, 2.87, and 1.26-fold at 0.5 h, 6 h, and 24 h higher than the control, respectively [28]. These results suggest that ScWRKY3 and ScWRKY4 may participate in sugarcane resistance to drought and salt stresses which may be mediated through ABA signaling
Summary
Plant growth and development are vulnerable to several external environmental challenges, such as drought, high salinity, cold, and pathogens. The transcription factors (TFs) in plant cells interact with specific DNA sequences in target gene promoters to activate or inhibit transcription and expression of target genes, thereby regulating the expression of these genes This modulation causes adaptation to the effects and damage from various stresses [2]. The DNA-binding domain is highly conserved, the overall structure of the WRKY proteins is highly diverse and can be divided into three groups (I, II, and III) including five subgroups (IIa-IIe) in group II. These groupings are categorized according to the number of WRKY domains and are based on features of the zinc finger-like motif [6,7]. WRKYs in groups I and III are involved in epidermal development, senescence, and abiotic stress, while WRKYs in group II are related to low phosphorus stress, disease resistance, secondary root formation, and abiotic stress, with a few exceptions observed [8]
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