SMALL GRAIN 1, which encodes a mitogen‐activated protein kinase kinase 4, influences grain size in rice

Abstract

These authors contributed equally to this work. SUMMARYAlthough grain size is one of the most important components of grain yield, little information is known about the mechanisms that determine final grain size in crops. Here we characterize rice small grain1 (smg1) mutants, which exhibit small and light grains, dense and erect panicles and comparatively slightly shorter plants. The short grain and panicle phenotypes of smg1 mutants are caused by a defect in cell proliferation. The smg1 mutations were identified, using a map-based cloning approach, in mitogen-activated protein kinase kinase 4 (OsMKK4). Relatively higher expression of OsMKK4/SMG1 was detected in younger organs than in older ones, consistent with its role in cell proliferation. Green fluorescent protein (GFP)-OsMKK4/SMG1 fusion proteins appear to be distributed ubiquitously in plant cells. Further results revealed that OsMKK4 influenced brassinosteroid (BR) responses and the expression of BR-related genes. Thus, our findings have identified OsMKK4 as a factor for grain size, and suggest a possible link between the MAPK pathways and BRs in grain growth.

A Rare Allele of GS2 Enhances Grain Size and Grain Yield in Rice

“…For example, THOUSAND-GRAIN WEIGHT 6 (TGW6) encodes a novel protein with indole-3-acetic acid (IAA)-glucose hydrolase activity and its loss-of-function allele enhances grain weight and yield (Ishimaru et al, 2013). SMALL GRAIN 1 (OsMKK4) influences brassinosteroid responses (Duan et al, 2014). BIG GRAIN2 (BG2) encodes OsCYP78A13, a member of the cytochrome P450 family, and elevated OsCYP78A13 expression promotes grain growth .…”

Mitogen-activated protein kinase cascades in signaling plant growth and development

“…In addition to embryogenesis, MAPKs also play vital roles in other stages of plant reproduction including anther development [40,41], ovule development [42], pollen development [37,43,44], pollen tube guidance [45], and seeds development [27,46]. Abnormal subcellular structure or cell division account for some of the mutant phenotypes, for example, a disrupted plasma membrane and unusual After the sensing of tissue/cell-specific input signaling molecules (e.g., peptide ligands), receptor-like protein kinase (RLK) receptors activate MAPK cascades in a spatiotemporal-specific manner, either directly or through additional mediator(s).…”

“…Due to functional redundancy or weak phenotypes, only a handful of MAPK components were identified based on forward genetic screens [11,[25][26][27][28]. By contrast, reverse genetic studies, in combination with conditional rescue, revealed many key functions of MAPK components in plant growth and development ( Figure 1).…”

The mitogen-activated protein kinase cascade MKK1–MPK4 mediates salt signaling in rice

“…Both OsMPK3 and OsMPK6 have been implicated in salt stress response [27,28]. OsMPK6 is activated during defense response, and is up-regulated by OsMKK4, which is also a gain development regulator [29][30][31]. Kumar et al (2008) showed that rice MKK1, 4, 6, 10-2 were induced by salt stress [32].…”