Ectopic overexpression of the transcription factor OsGLK1 induces chloroplast development in non-green rice cells.
For systematic and genome-wide analyses of rice gene functions, we took advantage of the full-length cDNA overexpresser (FOX) gene-hunting system and generated >12 000 independent FOX-rice lines from >25 000 rice calli treated with the rice-FOX Agrobacterium library. We found two FOX-rice lines generating green calli on a callus-inducing medium containing 2,4-D, on which wild-type rice calli became ivory yellow. In both lines, OsGLK1 cDNA encoding a GARP transcription factor was ectopically overexpressed. Using rice expression-microarray and northern blot analyses, we found that a large number of nucleus-encoded genes involved in chloroplast functions were highly expressed and transcripts of plastid-encoded genes, psaA, psbA and rbcL, increased in the OsGLK1-FOX calli. Transmission electron microscopy showed the existence of differentiated chloroplasts with grana stacks in OsGLK1-FOX calli cells. However, in darkness, OsGLK1-FOX calli did not show a green color or develop grana stacks. Furthermore, we found developed chloroplasts in vascular bundle and bundle sheath cells of coleoptiles and leaves from OsGLK1-FOX seedlings. The OsGLK1-FOX calli exhibited high photosynthetic activity and were able to grow on sucrose-depleted media, indicating that developed chloroplasts in OsGLK1-FOX rice calli are functional and active. We also observed that the endogenous OsGLK1 mRNA level increased synchronously with the greening of wild-type calli after transfer to plantlet regeneration medium. These results strongly suggest that OsGLK1 regulates chloroplast development under the control of light and phytohormones, and that it is a key regulator of chloroplast development.
Nakamura
Hidemitsu
H
Division of Genome and Biodiversity Research, National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki 305-8602, Japan. hnakamura@pgr1.ch.a.u-tokyo.ac.jp
Muramatsu
Masayuki
M
Hakata
Makoto
M
Ueno
Osamu
O
Nagamura
Yoshiaki
Y
Hirochika
Hirohiko
H
Takano
Makoto
M
Ichikawa
Hiroaki
H
D002734:Chlorophyll / Q000032:analysis; D002736:Chloroplasts / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D018076:DNA, Complementary / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D046529:Microscopy, Electron, Transmission; D020411:Oligonucleotide Array Sequence Analysis; D012275:Oryza / Q000235:genetics* / Q000378:metabolism; D010788:Photosynthesis; D018515:Plant Leaves / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
D018076:DNA, Complementary; D018744:DNA, Plant; C499672:Glk1 protein, Oryza sativa; D010940:Plant Proteins; D012333:RNA, Messenger; D014157:Transcription Factors; D002734:Chlorophyll