title: ZEBRA-NECROSIS, a thylakoid-bound protein, is critical for the photoprotection of developing chloroplasts during early leaf development.
abstract: The zebra-necrosis (zn) mutant of rice (Oryza sativa) produces transversely green/yellow-striped leaves. The mutant phenotype is formed by unequal impairment of chloroplast biogenesis before emergence from the leaf sheath under alternate light/dark or high/low temperatures (restrictive), but not under constant light and temperature (permissive) conditions. Map-based cloning revealed that ZN encodes a thylakoid-bound protein of unknown function. Virus-induced gene silencing of a ZN homolog in Nicotiana benthamiana causes leaf variegation with sporadic green/yellow sectors, indicating that ZN is essential for chloroplast biogenesis during early leaf development. Necrotic lesions often occur in the yellow sectors as a result of an excessive accumulation of reactive oxygen species (ROS). The phenotypic severity (leaf variegation and necrosis) and ROS levels are positively correlated with an increase in light intensity under restrictive conditions. In the mutant leaves, chlorophyll (Chl) metabolism, ROS scavenging activities, maximum quantum yield of photosystem II (PSII), and structures and functions of the photosynthetic complexes are normal in the Chl-containing cells, suggesting that ROS are mainly generated from the defective plastids of the Chl-free cells. The PSII activity of normal chloroplasts is hypersensitive to photoinhibition because the recovery rates of PSII are much slower. In the PSII repair, the degradation of damaged D1 is not impaired, suggesting a reduced activity of new D1 synthesis, possibly because of higher levels of ROS generated from the Chl-free cells by excess light. Together, we propose that ZN is required for protecting developing chloroplasts, especially during the assembly of thylakoid protein complexes, from incidental light after darkness.
authors.affiliation: Department of Plant Science, Plant Genomics and Breeding Institute, and Research Institute for Agriculture and Life Sciences, Seoul National University, Seoul 151-921, Korea.
authors.forename: Jinjie
authors.initials: J
authors.lastname: Li
authors.forename: Devendra
authors.initials: D
authors.lastname: Pandeya
authors.forename: Krishna
authors.initials: K
authors.lastname: Nath
authors.forename: Ismayil S
authors.initials: IS
authors.lastname: Zulfugarov
authors.forename: Soo-Cheul
authors.initials: SC
authors.lastname: Yoo
authors.forename: Haitao
authors.initials: H
authors.lastname: Zhang
authors.forename: Jeong-Hoon
authors.initials: JH
authors.lastname: Yoo
authors.forename: Sung-Hwan
authors.initials: SH
authors.lastname: Cho
authors.forename: Hee-Jong
authors.initials: HJ
authors.lastname: Koh
authors.forename: Do-Soon
authors.initials: DS
authors.lastname: Kim
authors.forename: Hak Soo
authors.initials: HS
authors.lastname: Seo
authors.forename: Byoung-Cheorl
authors.initials: BC
authors.lastname: Kang
authors.forename: Choon-Hwan
authors.initials: CH
authors.lastname: Lee
authors.forename: Nam-Chon
authors.initials: NC
authors.lastname: Paek
mesh_terms: D000595:Amino Acid Sequence; D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism / Q000528:radiation effects*; D003001:Cloning, Molecular; D020868:Gene Silencing; D018613:Microscopy, Confocal; D046529:Microscopy, Electron, Transmission; D008969:Molecular Sequence Data; D012275:Oryza / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D010641:Phenotype; D045332:Photosystem II Protein Complex / Q000378:metabolism; D020161:Physical Chromosome Mapping; D018515:Plant Leaves / Q000254:growth & development* / Q000528:radiation effects; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism; D020524:Thylakoids / Q000378:metabolism; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects
chemical_list: D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D017382:Reactive Oxygen Species; D002734:Chlorophyll