Abstract
Plant lectins are proteins that reversibly bind carbohydrates and are assumed to play an important role in plant development and resistance. Through the binding of carbohydrate ligands, lectins are involved in the perception of environmental signals and their translation into phenotypical responses. These processes require down-stream signaling cascades, often mediated by interacting proteins. Fusing the respective genes of two interacting proteins can be a way to increase the efficiency of this process. Most recently, proteins containing jacalin-related lectin (JRL) domains became a subject of plant resistance responses research. A meta-data analysis of fusion proteins containing JRL domains across different kingdoms revealed diverse partner domains ranging from kinases to toxins. Among them, proteins containing a JRL domain and a dirigent domain occur exclusively within monocotyledonous plants and show an unexpected high range of family member expansion compared to other JRL-fusion proteins. Rice, wheat, and barley plants overexpressing OsJAC1, a member of this family, are resistant against important fungal pathogens. We discuss the possibility that JRL domains also function as a decoy in fusion proteins and help to alert plants of the presence of attacking pathogens.
Highlights
The perception of external abiotic or biotic stimuli, such as changes in temperature or microbial attack, and their translation into adaptive cellular responses is essential for all living organisms
Lectin proteins bind to oligosaccharides and are well known as, e.g., extracellular domains of membrane-bound receptors, and so-called lectin receptor-like kinases (LecRLKs) [3]
LecRLKs can be seen as chimeric proteins with a binding and an action domain
Summary
The perception of external abiotic or biotic stimuli, such as changes in temperature or microbial attack, and their translation into adaptive cellular responses is essential for all living organisms. In addition to hormone receptors, plant proteins containing LRR domains are known as recognition proteins in plant immunity. In this context they are predicted to perceive attacking microbes and define pathogen recognition specificity [2]. Lectin proteins bind to oligosaccharides and are well known as, e.g., extracellular domains of membrane-bound receptors, and so-called lectin receptor-like kinases (LecRLKs) [3]. Our group reported on another type of chimeric, lectin-containing protein which is involved in mediating broad-spectrum disease resistance to monocotyledonous plants [4]. Chimeric JRL proteins with a dirigent domain, like TaVER2, TaHfr-1, TaJA1, and OsJAC1 were shown to be involved in plant defense (reviewed in [8]). We will summarize recent advances in our understanding of the role of chimeric lectin-containing proteins in plant defense, with special emphasis on those chimeric proteins containing a JRL domain
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