During Agrobacterium tumefaciens-mediated transformation of plant cells a part of the tumour-inducing plasmid, T-DNA, is integrated into the host genome. In addition, a number of virulence proteins... Show moreDuring Agrobacterium tumefaciens-mediated transformation of plant cells a part of the tumour-inducing plasmid, T-DNA, is integrated into the host genome. In addition, a number of virulence proteins are translocated into the host cell. The virulence protein VirE3 binds to the Arabidopsis thaliana pBrp protein, a plant-specific general transcription factor of the TFIIB family. To study a possible role for VirE3 in transcriptional regulation, we stably expressed virE3 in A. thaliana under control of a tamoxifen-inducible promoter. By RNA sequencing we showed that upon expression of virE3 the RNA levels of 607 genes were increased more than three-fold and those of 132 genes decreased more than three-fold. One of the strongly activated genes was that encoding VBF (At1G56250), an F-box protein that may affect the levels of the VirE2 and VIP1 proteins. Using Arabidopsis cell suspension protoplasts we showed that VirE3 stimulates the VBF promoter, especially when co-expressed with pBrp. Although pBrp is localized at the external surface of plastids, co-expression of VirE3 and pBrp in Arabidopsis cell suspension protoplasts resulted in the accumulation of pBrp in the nucleus. Our results suggest that VirE3 affects the transcriptional machinery of the host cell to favour the transformation process. Show less
Jasmonates (JAs) are plant hormones that regulate defense against microbial pathogens and insect herbivores via two antagonistic branches of the JAs signaling pathway leading to activation of... Show moreJasmonates (JAs) are plant hormones that regulate defense against microbial pathogens and insect herbivores via two antagonistic branches of the JAs signaling pathway leading to activation of distinct sets of defense genes. In Arabidopsis thaliana defense against herbivores is regulated by JAs alone which act via the receptor COI1 to cause degradation of Jasmonate-ZIM (JAZ) repressors thereby leading to activation of MYC transcription factors. In defense against microbial pathogens, JAs synergize with ethylene (ET). The APETALA2/Ethylene Response Factor (AP2/ERF)-domain transcription factor ORA59 integrates the JAs/ET signaling pathways and regulates resistance against necrotrophic pathogens. In search for ORA59-interacting proteins we found the CCCH zinc finger proteins ZFAR1 and ZFAR2, which in turn interacted with the JAs-responsive repressor JAZ1 to repress ORA59 activity. Gibberellins (GAs) modulate JA/ET signaling depending on DELLAs, key repressors of GA signaling. Here, we show that DELLAs directly interact in vivo and in vitro with ZFAR1, ZFAR2, and JAZ1. DELLAs repress the activity of ZFAR and JAZ1, and, thereby, enhance the activity of ORA59 resulting in higher expression levels of its target genes including PDF1.2. Thereby we provide a unifying model for the role of the JAZ repressors in the pathogen and herbivore branches of JAs signaling. Show less
Zhou, M.; Bakker, E.H.M.; Velzing, E.H.; Berger, S.; Oitzl, M.; Joels, M.; Krugers, H.J. 2010
Corticosteroid hormones are thought to promote optimal behavioral adaptation under fearful conditions primarily via glucocorticoid receptors (GRs) Here we examined - using pharmacological and... Show moreCorticosteroid hormones are thought to promote optimal behavioral adaptation under fearful conditions primarily via glucocorticoid receptors (GRs) Here we examined - using pharmacological and genetic approaches in mice - if mineralocorticoid receptors (MRs) also play a role in fearful memory formation As expected administration of the GR-antagonist RU38486 prior to training in a fear conditioning paradigm impaired contextual memory when tested 24 (but not when tested 3) h after training Tone-cue memory was enhanced by RU38486 when tested at 4 (but not 25) h after training Interestingly pre (but not post)-training administration of MR antagonist spironolactone impaired contextual memory both at 3 and 24 h after training Similar effects were also found in forebrain-specific MR knockout mice Spironolactone also impaired tone-cue memory but only at 4 h after training These results reveal that in addition to GRs - MRs also play a critical role in establishing fear memories particularly in the early phase of memory formation (C) 2010 Elsevier Inc All rights reserved Show less
