*Article* **A RING-Type E3 Ubiquitin Ligase,** *OsGW2,* **Controls Chlorophyll Content and Dark-Induced Senescence in Rice**

**Kyu-Chan Shim 1, Sun Ha Kim 1, Yun-A Jeon 1, Hyun-Sook Lee 1, Cheryl Adeva 1, Ju-Won Kang 2, Hyun-Jung Kim 3, Thomas H Tai 4,5 and Sang-Nag Ahn 1,\***


Received: 22 January 2020; Accepted: 27 February 2020; Published: 2 March 2020

**Abstract:** Leaf senescence is the final stage of plant development. Many internal and external factors affect the senescence process in rice (*Oryza sativa* L.). In this study, we identified *qCC2*, a major quantitative trait locus (QTL) for chlorophyll content using a population derived from an interspecific cross between *O. sativa* (*cv*. Hwaseong) and *Oryza grandiglumis*. The *O. grandiglumis* allele at *qCC2* increased chlorophyll content and delayed senescence. *GW2* encoding E3 ubiquitin ligase in the *qCC2* region was selected as a candidate for *qCC2*. To determine if *GW2* is allelic to *qCC2*, a *gw2*-knockout mutant (*gw2-ko*) was examined using a dark-induced senescence assay. *gw2-ko* showed delayed leaf senescence in the dark with down-regulated expression of senescence-associated genes (SAGs) and chlorophyll degradation genes (CDGs). The association of the *GW2* genotype with the delayed senescence phenotype was confirmed in an F2 population. RNA-seq analysis was conducted to investigate 30-day-old leaf transcriptome dynamics in Hwaseong and a backcross inbred line—CR2002—under dark treatment. This resulted in the identification of genes involved in phytohormone signaling and associated with senescence. These results suggested that transcriptional regulation was associated with delayed senescence in CR2002, and RING-type E3 ubiquitin ligase GW2 was a positive regulator of leaf senescence in rice.

**Keywords:** leaf senescence; rice; quantitative trait loci; transcriptome analysis
