OstMAPKKK5, a truncated mitogen-activated protein kinase kinase kinase 5, positively regulates plant height and yield in rice

Rice (Oryza sativa L.) is a major food crop worldwide. Plant height and yield are important agronomic traits of rice. Several genes regulating plant height and/or yield have been cloned. However, the molecular mechanisms coordinating plant height and yield are not fully characterized. Here, we report a novel gene, OstMAPKKK5 that encodes a truncated variant of a mitogen-activated protein kinase kinase kinase 5 (OsMAPKKK5) lacking an intact kinase domain. Transgenic plants overexpressing OstMAPKKK5 in indica cultivar 9311 showed increased plant height, grain length, grain width, 1000-grain weight, grain number per main panicle, and yield. Real-time quantitative PCR showed that OstMAPKKK5 was widely expressed in various tissues and developmental stages. The increased plant height and yield were attributed to enlarged cell size. Overexpression of OstMAPKKK5 led to higher contents of various forms of endogenous gibberellin (GA), especially the most common active forms, GA₁, GA₃, GA₄. We concluded that OstMAPKKK5 positively regulates plant height and yield in rice by affecting cell size, and that its underlying mechanism is based on increased endogenous GA content.