Abstract
The bZIP transcription factor VIP1 interacts with the Agrobacterium virulence protein VirE2, but the role of VIP1 in Agrobacterium-mediated transformation remains controversial. Previously tested vip1-1 mutant plants produce a truncated protein containing the crucial bZIP DNA-binding domain. We generated the CRISPR/Cas mutant vip1-2 that lacks this domain. The transformation susceptibility of vip1-2 and wild-type plants is similar. Because of potential functional redundancy among VIP1 homologs, we tested transgenic lines expressing VIP1 fused to a SRDX repression domain. All VIP1-SRDX transgenic lines showed wild-type levels of transformation, indicating that neither VIP1 nor its homologs are required for Agrobacterium-mediated transformation. Because VIP1 is involved in innate immune response signaling, we tested the susceptibility of vip1 mutant and VIP1-SRDX plants to Pseudomonas syringae and Botrytis cinerea. vip1 mutant and VIP1-SRDX plants show increased susceptibility to B. cinerea but not to P. syringae infection, suggesting a role for VIP1 in B. cinerea, but not in P. syringae, defense signaling. B. cinerea susceptibility is dependent on abscisic acid (ABA) which is also important for abiotic stress responses. The germination of vip1 mutant and VIP1-SRDX seeds is sensitive to exogenous ABA, suggesting a role for VIP1 in response to ABA. vip1 mutant and VIP1-SRDX plants show increased tolerance to growth in salt, indicating a role for VIP1 in response to salt stress.
Highlights
Virulent strains of the soil bacterium Agrobacterium tumefaciens cause the tumorigenic disease crown gall
We examined vip1-2 plants for abnormal growth or developmental phenotypes. vip1-2 plants exhibited increased rosette and leaf size compared to wild-type plants vip1-2 Plants Show Wild-Type Susceptibility to AgrobacteriumMediated Transformation
The three independent lines of VirE2-interacting protein 1 (VIP1)-SRDX plants used in this study all showed high expression levels of VIP1-SRDX and root waving phenotypes in a previous study (Tsugama et al, 2016), indicating the efficacy of the EAR motif in repressing expression of genes regulated by VIP1 family members
Summary
Virulent strains of the soil bacterium Agrobacterium tumefaciens cause the tumorigenic disease crown gall. The effector protein VirE2 has non-specific single-stranded DNA-binding activity and is thought to coat single-stranded T-DNA (T-strands) after entry into the plant cell (Citovsky et al, 1992), protecting T-strands from nucleolytic degradation (Yusibov et al, 1994; Rossi et al, 1996) In addition to this structural role, VirE2 interacts with a number of plant proteins including VirE2-interacting protein 1 (VIP1; Tzfira et al, 2001) and VIP2 (Anand et al, 2007). VirE2 nuclear import has been attributed to its interaction with VIP1 (Tzfira et al, 2001), a protein that localizes to both the cytoplasm and the nucleus (Djamei et al, 2007; Shi et al, 2014). VIP1 may be important for defense responses against the fungus Botrytis cinerea, for abscisic acid (ABA) signaling, and for growth under salt stress conditions
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