ArabidopsisSigma Factor Binding Proteins Are Activators of the WRKY33 Transcription Factor in Plant Defense

Abstract

Necrotrophic pathogens are important plant pathogens that cause many devastating plant diseases. Despite their impact, our understanding of the plant defense response to necrotrophic pathogens is limited. The WRKY33 transcription factor is important for plant resistance to necrotrophic pathogens; therefore, elucidation of its functions will enhance our understanding of plant immunity to necrotrophic pathogens. Here, we report the identification of two WRKY33-interacting proteins, nuclear-encoded SIGMA FACTOR BINDING PROTEIN1 (SIB1) and SIB2, which also interact with plastid-encoded plastid RNA polymerase SIGMA FACTOR1. Both SIB1 and SIB2 contain an N-terminal chloroplast targeting signal and a putative nuclear localization signal, suggesting that they are dual targeted. Bimolecular fluorescence complementation indicates that WRKY33 interacts with SIBs in the nucleus of plant cells. Both SIB1 and SIB2 contain a short VQ motif that is important for interaction with WRKY33. The two VQ motif-containing proteins recognize the C-terminal WRKY domain and stimulate the DNA binding activity of WRKY33. Like WRKY33, both SIB1 and SIB2 are rapidly and strongly induced by the necrotrophic pathogen Botrytis cinerea. Resistance to B. cinerea is compromised in the sib1 and sib2 mutants but enhanced in SIB1-overexpressing transgenic plants. These results suggest that dual-targeted SIB1 and SIB2 function as activators of WRKY33 in plant defense against necrotrophic pathogens.

The VQ Motif-Containing Protein Family of Plant-Specific Transcriptional Regulators

“…3A). Consistently, VQ23 coprecipitated with the WRKY33/DNA complex in an electrophoretic mobility shift assay, and VQ23 and VQ16 exhibit transcriptional activation properties (Lai et al, 2011;Li et al, 2014). By contrast, the interaction between VQ9 and WRKY8 represses the DNA-binding activity of WRKY8 ( Fig.…”

“…However, it was reported that VQ23 overexpression plants do not differ from the control with respect to their sensitivity to the virulent strain P. syringae pv tobacco (Pst) DC3000 (Narusaka et al, 2008). VQ16/SIB2 plays a redundant role in response to B. cinerea infection with VQ23 (Lai et al, 2011), consistent with their evolutionary relatedness in VQ group VI.…”

“…The increased resistance of VQ23 overexpression plants to B. cinerea is dependent on functional WRKY33 (Xie et al, 2010;Lai et al, 2011). Thus, VQ23 positively regulates the plant defense response against both necrotrophic and biotrophic pathogens likely via a WRKY-dependent signaling pathway.…”

“…The transcription of VQ genes is modulated by multiple endogenous and environmental signals, consistent with their diverse roles in stress responses and during plant growth and development. For instance, B. cinerea infection and SA treatment rapidly and strongly induce VQ23 and VQ16 transcript levels (Narusaka et al, 2008;Xie et al, 2010;Lai et al, 2011). VQ22 transcript is significantly increased upon JA treatment and quickly accumulates after mechanical wounding (Hu et al, 2013a).…”

MED18 interaction with distinct transcription factors regulates multiple plant functions

“…The DNAbinding activity of WRKY33 is controlled by SIB1 (SIGMA FACTOR-BINDING PROTEIN1) and SIB2 (ref. 17), and its transcription activity is enhanced by MPK3/MPK6 phosphorylation 18 . Modification of histone tails is another layer of transcriptional control that was found to affect plant immune responses [19][20][21] .…”