A RING-type E3 ubiquitin ligase, OsGW2 controls chlorophyll content and dark-induced senescence in rice

Authors: SHIM, KYU-CHAN - Chungnam National University; KIM, SUN HA - Chungnam National University; JEON, YUN-A - Chungnam National University; LEE, HYUN-SOOK - Chungnam National University; ADEVA, CHERYL - Chungnam National University; KANG, JU-WON - Rural Development Administration - Korea; KIM, HYUNJUNG - Lg Chem; Tai, Thomas; AHN, SANG-NAG - Chungnam National University

Submitted to: International Journal of Molecular Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2020
Publication Date: 3/2/2020
Citation: Shim, K., Kim, S., Jeon, Y., Lee, H., Adeva, C., Kang, J., Kim, H., Tai, T., Ahn, S. 2020. A RING-type E3 ubiquitin ligase, OsGW2 controls chlorophyll content and dark-induced senescence in rice. International Journal of Molecular Sciences. 21(5). https://doi.org/10.3390/ijms21051704.
DOI: https://doi.org/10.3390/ijms21051704

Interpretive Summary: Senescence refers to the aging process in organisms. In plants, leaf senescence is characterized by the degradation or loss of the chlorophyll, the green pigment which plays a key role in photosynthesis. This occurs naturally as plants age and can also be induced in leaves which are incubate in complete darkness. In this study, a major quantitative trait locus (QTL) controlling chlorophyll content named qCC2 was identified by evaluating a rice F2 genetic mapping population that was developed from a rice line containing genes from a wild species Oryza grandiglumis and an elite rice variety Hwaseong. It was determined that qCC2 from Oryza grandiglumis delayed senescence in leaf tissues that are placed in the dark. A candidate gene underlying qCC2 was identified and evidence for its involvement was obtained by analyzing a rice mutant in which this gene, a RING-type E3 ubiquitin ligase called GW2, was disrupted (i.e. non-functional). In addition, gene expression was examined in plants with delayed senescence in the dark and those with a normal response to incubation in the dark to further characterize the dark-induced chlorophyll degradation/leaf senescence phenomenon.

Technical 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 QTL for chlorophyll content using a population derived from an interspecific cross between O. sativa (cv. Hwaseong) and O. 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). 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 suggest that transcriptional regulation is associated with delayed senescence in CR2002 and RING-type E3 ubiquitin ligase GW2 is a positive regulator of leaf senescence in rice.