Abstract
Leucine-rich repeat receptor-like kinases (LRR-RLKs) are widespread in different plant species and play important roles in growth and development. Germination inhibition is vital for the completion of seed maturation and cell expansion is a fundamental cellular process driving plant growth. Here, we report genetic and structural characterizations of a functionally uncharacterized LRR-RLK, named GRACE (Germination Repression and Cell Expansion receptor-like kinase). Overexpression of GRACE in Arabidopsis exhibited delayed germination, enlarged cotyledons, rosette leaves and stubbier petioles. Conversely, these phenotypes were reversed in the T-DNA insertion knock-down mutant grace-1 plants. A crystal structure of the extracellular domain of GRACE (GRACE-LRR) determined at the resolution of 3.0 Å revealed that GRACE-LRR assumed a right-handed super-helical structure with an island domain (ID). Structural comparison showed that structure of the ID in GRACE-LRR is strikingly different from those observed in other LRR-RLKs. This structural observation implies that GRACE might perceive a new ligand for signaling. Collectively, our data support roles of GRACE in repressing seed germination and promoting cell expansion of Arabidopsis, presumably by perception of unknown ligand(s).
Highlights
IntroductionPlants develop powerful signal communication systems to survive in the constantly changed environment
As sessile organisms, plants develop powerful signal communication systems to survive in the constantly changed environment
green fluorescent protein (GFP) fluoresce could be observed on membrane of epidermis and protoplasts of OE1 leaves. These results suggest that GRACE encodes a membrane protein, as predicted by an LRR-receptor-like kinases (RLKs)
Summary
Plants develop powerful signal communication systems to survive in the constantly changed environment. Membrane-localized receptor-like kinases (RLKs) are important to perceive signals from highly dynamic internal growing processes and various environmental conditions, transmitting them into cell to regulate growth, development, defense processes, and abiotic/biotic stresses (Li and Tax, 2013). LRR-RLKs are the largest and well-studied subfamily of RLKs in Arabidopsis (Shiu and Bleecker, 2001a,b). Functions for most of the LRR-RLKs are still elusive (Wu et al, 2016). LRR-RLKs have an extracellular LRR region typically responsible for signal recognition, a singlepassing transmembrane region, and an intracellular serine/threonine kinase domain for signal initiation (Kobe and Kajava, 2001; Botos et al, 2011; Li and Tax, 2013; Zhang and Thomma, 2013).
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