Abstract
Multigene families coding for valine-glutamine (VQ) proteins have been identified in all kind of plants but chlorophytes. VQ proteins are transcriptional regulators, which often interact with WRKY transcription factors to regulate gene expression sometimes modulated by reversible phosphorylation. Different VQ-WRKY complexes regulate defense against varied pathogens as well as responses to osmotic stress and extreme temperatures. However, despite these well-known functions, new regulatory activities for VQ proteins are still to be explored. Searching public Arabidopsis thaliana transcriptome data for new potential targets of VQ-WRKY regulation allowed us identifying several VQ protein and WRKY factor encoding genes that were differentially expressed in oxygen-related processes such as responses to hypoxia or ozone-triggered oxidative stress. Moreover, some of those were also differentially regulated upon nitric oxide (NO) treatment. These subsets of VQ and WRKY proteins might combine into different VQ-WRKY complexes, thus representing a potential regulatory core of NO-modulated and O2-modulated responses. Given the increasing relevance that gasotransmitters are gaining as plant physiology regulators, and particularly considering the key roles exerted by O2 and NO in regulating the N-degron pathway-controlled stability of transcription factors, VQ and WRKY proteins could be instrumental in regulating manifold processes in plants.
Highlights
A group of proteins containing the FxxxVQxxTG motif was first identified in Arabidopsis thaliana and named as valine-glutamine (VQ) proteins (Morikawa et al, 2002; Xie et al, 2010; Cheng et al, 2012)
After the initial identification in Arabidopsis, VQ protein families have been identified in a large number of plants, including rice, soybean, grapevine, Chinese cabbage, maize, banana, bamboo, strawberry, apple, tea plant, Eucalyptus, tobacco, chick pea, and alfalfa (Kim et al, 2013; Li et al, 2014a; Wang et al, 2014, 2015a, 2017; Zhang et al, 2015; Song et al, 2016; Ye et al, 2016; Zhou et al, 2016; Dong et al, 2018; Guo et al, 2018; Zhong et al, 2018; Garrido-Gala et al, 2019; Yan et al, 2019; Ling et al, 2020; Liu et al, 2020)
While VQ proteins were initially thought to be plant specific proteins (Jing and Lin, 2015), recent studies on diverse genomes concluded that VQ proteins are present in bacteria, fungi, and lower animals but not in algae (Jiang et al, 2018)
Summary
A group of proteins containing the FxxxVQxxTG motif was first identified in Arabidopsis thaliana and named as valine-glutamine (VQ) proteins (Morikawa et al, 2002; Xie et al, 2010; Cheng et al, 2012). Reports during the last decade supported the function of VQ proteins as relevant regulators of plant defense against pathogens and pests.
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