Abstract
Leucine-rich repeat (LRR)-receptor-like protein kinases (LRR-RLKs) play vital roles in plant growth, development, and responses to environmental stresses. In this study, a new LRR-RLK gene, ZmRLK7, was isolated from maize, and its function within plant development was investigated through ectopic expression in Arabidopsis. The spatial expression pattern analysis reveals that ZmRLK7 is highly expressed in embryos prior to programmed cell death (PCD) of starchy endosperm tissues, and its encoded protein has been localized to both plasm and nuclear membranes subcellularly. Overexpression of sense ZmRLK7 reduced the plant height, organ size (e.g., petals, silique, and seeds), and 1000-seed weight in transgenic lines, while the antisense transgene enlarged these traits. Cytological analysis suggested that ZmRLK7 negatively regulates petal size through restricting both cell expansion and proliferation. In addition, abnormal epidermal cell structure was observed, and the stomata number decreased obviously in sense ZmRLK7 transgenic lines with a lower stomatal index than that in the wild type. Quantitative RT-PCR analysis indicated that transcript levels of genes that are involved in the brassinosteroid and ERACTA signaling pathways were coordinately altered, which could partially explain the phenotypic variation. Moreover, overexpression of antisense ZmRLK7 substantially rescued the Arabidopsis bak1-3 mutant phenotype. All these results together suggest that ZmRLK7 can serve as an important regulator in regulating plant architecture and organ size formation. This work will provide insight into the function of ZmRLK7 in maize.
Highlights
In plant growth and development, the organ size and shape of a plant are complicated biological features that are mainly determined by coordination of cell proliferation, expansion, and differentiation (Mizukami, 2001)
Analyses of the structural properties of the ZmRLK7-predicted protein using the SMART program indicate that this protein is a putative leucine-rich repeat receptor-like kinase (LRR-receptor-like kinases (RLKs)) featured with typical domains (Figure 1A)
A putative extracellular domain in the N-terminal region, containing 10 tandem copies of a 24~25 amino acid leucine-rich repeat (LRR), and a transmembrane domain was identified at amino acid positions 755–777
Summary
In plant growth and development, the organ size and shape of a plant are complicated biological features that are mainly determined by coordination of cell proliferation, expansion, and differentiation (Mizukami, 2001). The BRI1ASSOCIATED KINASE-1 (BAK1) receptor, identified as a signaling partner of another LRR-receptor kinase, the brassinosteroid (BR) receptor BRI1 (BRASSINOSTEROID INSENSITIVE1), positively regulated a BR-dependent plant growth pathway (Li et al, 2002; Clouse, 2011). ERECTA (ER), another LRR receptor-like Ser/Thr kinase, functions synergistically with its two homologs ER-LIKE1 (ERL1) and ERL2 (forming the ER family) to regulate multiple developmental processes, including petiole length, inflorescence architecture, ovule development, and stomatal patterning (Torii et al, 1996; Shpak et al, 2004; Pillitteri et al, 2007a; van Zanten et al, 2009; Shpak, 2013)
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