Knights in Action: Lectin Receptor-Like Kinases in Plant Development and Stress Responses

Abstract

The Receptor-Like Kinase (RLK) is a vast protein family with over 600 genes in Arabidopsis and 1100 in rice. The Lectin RLK (LecRLK) family is believed to play crucial roles in saccharide signaling as well as stress perception. All the LecRLKs possess three domains: an N-terminal lectin domain, an intermediate transmembrane domain, and a C-terminal kinase domain. On the basis of lectin domain variability, LecRLKs have been subgrouped into three subclasses: L-, G-, and C-type LecRLKs. While the previous studies on LecRLKs were dedicated to classification, comparative structural analysis and expression analysis by promoter-based studies, most of the recent studies on LecRLKs have laid special emphasis on the potential of this gene family in regulating biotic/abiotic stress and developmental pathways in plants, thus making the prospects of studying the LecRLK-mediated regulatory mechanism exceptionally promising. In this review, we have described in detail the LecRLK gene family with respect to a historical, evolutionary, and structural point of view. Furthermore, we have laid emphasis on the LecRLKs roles in development, stress conditions, and hormonal response. We have also discussed the exciting research prospects offered by the current knowledge on the LecRLK gene family. The multitude of the LecRLK gene family members and their functional diversity mark these genes as both interesting and worthy candidates for further analysis, especially in the field of crop improvement.

Lectin domains at the frontiers of plant defense

“…Typically, LecRKs are two-domain proteins composed of an N-terminal extracellular lectin domain and a C-terminal cytosolic Ser/Thr kinase domain, separated by a transmembrane region ( Figure 1C ). Based on their lectin domain LecRKs are classified into 4 types; G-, C-, L-, and LysM-type (Singh and Zimmerli, 2013; Vaid et al, 2013). Although these LecRKs consist of at least one domain that shows striking sequence similarity with a lectin motif, very little information is available with respect to the ability of this domain to recognize and interact with specific carbohydratestructures.…”

The Receptor-Like Kinase SIT1 Mediates Salt Sensitivity by Activating MAPK3/6 and Regulating Ethylene Homeostasis in Rice

“…Among the 610 RLKs in Arabidopsis thaliana and 1100 RLKs in rice (Oryza sativa) (Shiu et al, 2004), a small number have been characterized as receptors for phytohormones, polypeptides, and pathogens. Each of these RLKs can rapidly initiate signaling through the formation of oligomers and cross-phosphorylation of the intracellular serine/threonine kinase domain upon ligand binding (Diévart and Clark, 2004) and together they play diverse roles in plant development and pathogen resistance (Antolín-Llovera et al, 2012;Osakabe et al, 2013); some RLKs are also reported to function in drought and salt responses and tolerance (de Lorenzo et al, 2009;Ouyang et al, 2010;Marshall et al, 2012;Vaid et al, 2013). Rice SIK1(Os06g03970), a leucine-rich repeat RLK that is expressed most strongly in stem and panicle but which is not expressed in root, was found to be salt-inducible and a positive regulator of salt tolerance (Ouyang et al, 2010).…”

“…They are believed to be involved in saccharide signaling, and they play roles in self-incompatibility and in plant defenses against pathogens and pests, based on the known functions of lectin proteins in cell recognition. In addition, they are involved in plant salt stress and abscisic acid (ABA) responses (Vaid et al, 2013). However, whether these RLKs are involved in stress perception or whether they mediate salt signal relay has not been clarified.…”

Pea lectin receptor-like kinase functions in salinity adaptation without yield penalty, by alleviating osmotic and ionic stresses and upregulating stress-responsive genes

“…LecRLK is an extensively duplicated family with 173 and 75 members in rice and Arabidopsis, respectively (Vaid et al 2012). LecRLKs are plasma membrane proteins with an extracellular region resembling lectin proteins, followed a single-pass transmembrane region and a kinase domain (Vaid et al 2013). The kinase domain, mediating the downstream signaling, is highly conserved among the whole RLK family while the extracellular lectin domain which is the signal perception/recognition domain, is variable even within the LecRLK family (Vaid et al 2012).…”