Abstract
Key messageNovel mutations ofOsCOP1 were identified to be responsible for yellowish pericarp and embryolethal phenotype, which revealed that OsCOP1 plays a crucial role in flavonoid biosynthesis andembryogenesis in rice seed.Successful production of viable seeds is a major component of plant life cycles, and seed development is a complex, highly regulated process that affects characteristics such as seed viability and color. In this study, three yellowish-pericarp embryo lethal (yel) mutants, yel-hc, yel-sk, and yel-cc, were produced from three different japonica cultivars of rice (Oryza sativa L). Mutant seeds had yellowish pericarps and exhibited embryonic lethality, with significantly reduced grain size and weight. Morphological aberrations were apparent by 5 days after pollination, with abnormal embryo development and increased flavonoid accumulation observed in the yel mutants. Genetic analysis and mapping revealed that the phenotype of the three yel mutants was controlled by a single recessive gene, LOC_Os02g53140, an ortholog of Arabidopsis thaliana CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1). The yel-hc, yel-sk, and yel-cc mutants carried mutations in the RING finger, coiled-coil, and WD40 repeat domains, respectively, of OsCOP1. CRISPR/Cas9-targeted mutagenesis was used to knock out OsCOP1 by targeting its functional domains, and transgenic seed displayed the yel mutant phenotype. Overexpression of OsCOP1 in a homozygous yel-hc mutant background restored pericarp color, and the aberrant flavonoid accumulation observed in yel-hc mutant was significantly reduced in the embryo and endosperm. These results demonstrate that OsCOP1 is associated with embryo development and flavonoid biosynthesis in rice grains. This study will facilitate a better understanding of the functional roles of OsCOP1 involved in early embryogenesis and flavonoid biosynthesis in rice seeds.
Highlights
Light is a crucial signaling component that controls a variety of physiological and developmental processes in morphogenesis, germination, and flowering in plants
CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) acts as an E3 ubiquitin ligase to repress light signaling by targeting numerous photomorphogenic-promoting transcription factors, including ELONGATED HYPOCOTYL5 (HY5), HY5-HOMOLOG (HYH), LONG AFTER FARRED1 (LAF1), and LONG HYPOCOTYL IN FAR-RED1 (HFR1), for ubiquitination and degradation in the nucleus (Holm et al 2002; Osterlund et al 2000; Seo et al 2003; Yang et al 2005)
Three yellowish-pericarp embryo lethal mutants, yel-hc, yel-sk, and yel-cc, were derived from japonica rice cultivars Hwacheong, Samkwang, and Chucheong, respectively, by induction with N-methyl-N-nitrosourea. Due to their embryonic lethality, the mutants were maintained as heterozygotes. F2 mapping populations were developed from crosses between the three heterozygous yel mutants and Milyang 23 (M.23, Korean indica-type rice). F2 populations derived from crosses between the three heterozygous yel mutants and their respective wild types, Hwacheong, Samkwang, and Chucheong, were used to calculate segregation ratios. F2 populations, wild-type varieties, and yel mutants were cultivated in a paddy field at the Experimental Farm of Seoul National University, Suwon, Korea
Summary
Light is a crucial signaling component that controls a variety of physiological and developmental processes in morphogenesis, germination, and flowering in plants. Light signaling is involved in metabolic alterations, including the biosynthesis of chlorophyll (Ilag et al 1994; Pattanayak et al 2005) and several types of pigments (Takos et al 2006; von Lintig et al 1997; Zoratti et al 2014). These light signaling pathways are triggered upon perception of light signals by multiple photoreceptors, such as red/far red light-sensing phytochromes (phyA to phyE), UV-A/blue light-sensing cryptochromes (cry and cry2), phototropins. In addition to acting as a repressor of photomorphogenesis (Ang et al 1998; Deng et al 1991; Ma et al 2002; Seo et al 2003), COP1 functions as a crucial regulator in several biological processes, such as flowering
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