The PLASTID DIVISION1 and 2 Components of the Chloroplast Division Machinery Determine the Rate of Chloroplast Division in Land Plant Cell Differentiation  

Abstract

In most algae, the chloroplast division rate is held constant to maintain the proper number of chloroplasts per cell. By contrast, land plants evolved cell and chloroplast differentiation systems in which the size and number of chloroplasts change along with their respective cellular function by regulation of the division rate. Here, we show that PLASTID DIVISION (PDV) proteins, land plant-specific components of the division apparatus, determine the rate of chloroplast division. Overexpression of PDV proteins in the angiosperm Arabidopsis thaliana and the moss Physcomitrella patens increased the number but decreased the size of chloroplasts; reduction of PDV levels resulted in the opposite effect. The level of PDV proteins, but not other division components, decreased during leaf development, during which the chloroplast division rate also decreased. Exogenous cytokinins or overexpression of the cytokinin-responsive transcription factor CYTOKININ RESPONSE FACTOR2 increased the chloroplast division rate, where PDV proteins, but not other components of the division apparatus, were upregulated. These results suggest that the integration of PDV proteins into the division machinery enabled land plant cells to change chloroplast size and number in accord with the fate of cell differentiation.

Functional Characterization of the GATA Transcription Factors GNC and CGA1 Reveals Their Key Role in Chloroplast Development, Growth, and Division in Arabidopsis

“…Growth of the wild type with 1 mM BA results in a 1.41-fold increase in the chloroplast number per cell (Fig. 8B), consistent with a cytokinin effect on chloroplast division (Okazaki et al, 2009). Although the chloroplast number per cell of the gnc cga1 mutant is similar to that of the wild type in the untreated sample, it exhibits reduced sensitivity to cytokinin, resulting in significantly lower numbers of chloroplasts than the wild type in the presence of 1 mM BA (1.25-fold cytokinin-dependent increase in chloroplast number per cell for gnc cga1 compared with 1.41-fold increase for the wild type; Fig.…”

“…S10). The effects of GNC/CGA1 on cell expansion are likely related to their role in the repression of GA signaling (Richter et al, 2010), while their effects on chloroplast size suggest a role in the regulation of chloroplast division (Okazaki et al, 2009). The effect of GNC on chloroplast size and division provides an explanation, at least in part, for the greater number of chloroplasts reported in leaves of GNC overexpression lines (Hudson et al, 2011).…”

“…Cytokinin stimulates chloroplast division in cotyledons, resulting in a smaller size but increased numbers of chloroplasts (Okazaki et al, 2009). Therefore, we examined the effects of cytokinin on chloroplast size and number in the wild type, the gnc cga1 mutant, and the GNC overexpression lines (Fig.…”

“…The glk1 glk2 double mutant is pale green with a severe reduction in thylakoids, and the GLK transcription factors promote the expression of many nucleus-encoded photosynthetic genes that are associated with chlorophyll biosynthesis and light-harvesting functions ). In addition, and tying back to the role of cytokinin in regulating chloroplast biogenesis, overexpression of the cytokinin-regulated transcription factor CYTOKININ RESPONSE FACTOR2 (CRF2; Rashotte et al, 2006) increases the chloroplast division rate by up-regulating the protein level of PLASTID DIVISION2 (PDV2; Okazaki et al, 2009).…”

Rice Cytokinin GATA Transcription Factor1 Regulates Chloroplast Development and Plant Architecture

“…In Arabidopsis, we analyzed the expression of chloroplast division factors known to alter chloroplast number, including plastid division and accumulation and replication of cholorplast genes (Miyagishima et al, 2006;Glynn et al, 2008;Okazaki et al, 2009). However, these genes are not expressed in a similar fashion (Jen et al, 2006) and were not found to be significantly altered in Arabidopsis CGA1 transgenic lines (Hudson et al, 2011).…”