ZEBRA-NECROSIS, a thylakoid-bound protein, is critical for the photoprotection of developing chloroplasts during early leaf development.
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.
Li
Jinjie
J
Department of Plant Science, Plant Genomics and Breeding Institute, and Research Institute for Agriculture and Life Sciences, Seoul National University, Seoul 151-921, Korea.
Pandeya
Devendra
D
Nath
Krishna
K
Zulfugarov
Ismayil S
IS
Yoo
Soo-Cheul
SC
Zhang
Haitao
H
Yoo
Jeong-Hoon
JH
Cho
Sung-Hwan
SH
Koh
Hee-Jong
HJ
Kim
Do-Soon
DS
Seo
Hak Soo
HS
Kang
Byoung-Cheorl
BC
Lee
Choon-Hwan
CH
Paek
Nam-Chon
NC
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
D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D017382:Reactive Oxygen Species; D002734:Chlorophyll