Chloroplast DNA-binding protease (CND41), chloroplast development and plant growth

Abstract

CND41, a 41-kD DNA-binding protease in chloroplasts, has been isolated recently and its possible function as a negative regulator of chloroplast gene expression has been characterized1). Further characterization of protease function of CND41 indicated that CND41 would be involved in the degradation of Rubisco (see Y. Kato et al. abstract). Here, we report the regulation of CND41 expression and its pleiotropic effects on chloroplast development and plant growth. As we reported previously, CND41 accumulated in non-photosynthetic tissues/cells, especially non-photosynthetic cultured cells and stem. Analysis of CND41 transcript accumulation indicated that sugar is an important regulator of CND41 expression both in cultured cells and plants. Dissection of sugar-induced signal transduction indicated that this induction is hexokinase-independent, not sucrose-specific and phosphate-depletion independent. GUS activity in transgenic tobacco harboring CND41 promoter::GUS showed that sugar induction was transcriptionally regulated. On the other hand, transgenic tobacco with reduced CND41 showed that CND41 is also involved in plant growth and chloroplast development; Plastid development in shoot apex cells was more accelerated in low CND41 tobacco than wild type. Low CND41 tobacco also showed a dwarf phenotype. Active gibberellin (GA1) application restored the growth of low CND41 tobacco and analysis of gibberellin content confirmed the reduction of active GA in transformant. Relationship of CND41, chloroplast development and plant growth is discussed.