PARENT SESSION
Posters P7D Chloroplast factories and transformation. Abstracts (754-758)

Regulation and manipulation of transcription through dephosphorylation of factor in the chloroplast. Hirokazu Kobayashi^*,1, Hideki Kato¹, Masanori Shimizu¹, ¹ Laboratory of Plant Cell Technology, Shizuoka, Shizuoka, Japan

ABSTRACT- Photosynthesis occurs in the chloroplast in the light, when the photosystem (PS) reaction centers, especially D1 and D2 proteins in PS II, suffer from irreversible damage during photosynthesis, and those damaged are immediately replaced with newly synthesized ones to sustain the function. Expression of their genes encoded in the chloroplast genome must be regulated through sensing the environmental change. Transcription of most photosynthesis genes in the chloroplast is accomplished with bacterial-type plastid-encoded RNA polymerase (PEP), which requires multiple nucleus-encoded factors destined for the chloroplast. We have made Arabidopsis transgenic with SIG1 molecule, the major species of factors, with or without deletion of putative phosphorylation sites, to express it ectopically. The plants were labeled with [³²P]orthophosphate in vivo, and SIG1 was recovered with antibodies. Determination of molecular mass of complexes associated with SIG1, elucidated the fact that SIG1 competed to bind with core enzyme to generate transcriptionally-active holoenzyme in the light, whereas SIG1 phosphorylated at Thr-170 was more preferentially associated than unphoshorylated one with core enzyme to interfere with transcription in the dark. Elimination of the phosphorylation site on SIG1 may make transcription of chloroplast genes independent of redox-regulated suppression, being applicable to chloroplast factories for enhanced expression of foreign genes.

KEY WORDS: phosphorylation, factor, chloroplast, Arabidopsis