Physiological and Transcriptomic Evidence for a Close Coupling between Chloroplast Ontogeny and Cell Cycle Progression in the Pennate DiatomSeminavis robusta

Jeroen Gillard,Katrijn Vannerum,Lieven De Veylder,Sofie D'Hondt,Wim Vyverman,Cindy Martens,Marnik Vuylsteke,Valerie Devos,Marie J.J Huysman,Victor A Chepurnov,Koen Sabbe,Pieter Vanormelingen,Dirk Inzé

doi:10.1104/pp.108.122176

Jeroen Gillard, Katrijn Vannerum + Show 11 more

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https://doi.org/10.1104/pp.108.122176

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Abstract

Despite the growing interest in diatom genomics, detailed time series of gene expression in relation to key cellular processes are still lacking. Here, we investigated the relationships between the cell cycle and chloroplast development in the pennate diatom Seminavis robusta. This diatom possesses two chloroplasts with a well-orchestrated developmental cycle, common to many pennate diatoms. By assessing the effects of induced cell cycle arrest with microscopy and flow cytometry, we found that division and reorganization of the chloroplasts are initiated only after S-phase progression. Next, we quantified the expression of the S. robusta FtsZ homolog to address the division status of chloroplasts during synchronized growth and monitored microscopically their dynamics in relation to nuclear division and silicon deposition. We show that chloroplasts divide and relocate during the S/G2 phase, after which a girdle band is deposited to accommodate cell growth. Synchronized cultures of two genotypes were subsequently used for a cDNA-amplified fragment length polymorphism-based genome-wide transcript profiling, in which 917 reproducibly modulated transcripts were identified. We observed that genes involved in pigment biosynthesis and coding for light-harvesting proteins were up-regulated during G2/M phase and cell separation. Light and cell cycle progression were both found to affect fucoxanthin-chlorophyll a/c-binding protein expression and accumulation of fucoxanthin cell content. Because chloroplasts elongate at the stage of cytokinesis, cell cycle-modulated photosynthetic gene expression and synthesis of pigments in concert with cell division might balance chloroplast growth, which confirms that chloroplast biogenesis in S. robusta is tightly regulated.

Highlights

Jeroen Gillard, Valerie D evos, Marie J.J
U sing light deprivation and tw o cell cycle inhibitors, w e investigated w hether a relationship exists between the cell cycle checkpoints and the chloroplast division cycle
A putative reason is that m ostly polyplastidic centric diatom s have been stud ied in which the small chloroplasts are stochastically partitioned upon cell division and, have not such an obvious developm ental cycle

Summary

Introduction

Jeroen Gillard, Valerie D evos, Marie J.J. H uysm an, Lieven D e Veylder, Sofie D 'H ondt, Cindy Martens, Pieter Vanorm elingen, Katrijn Vannerum, Koen Sabbe, Victor A. Because chloroplasts elongate at the stage of cytokinesis, cell cycle-modulated photosynthetic gene expression and synthesis of pigm ents in concert w ith cell division might balance chloroplast growth, w hich confirms that chloroplast biogenesis in S. robusta is tightly regulated. The outerm ost pair of m em branes is connected w ith the nuclear envelope in anumb er of diatom s (Stoerm er et al, 1965; Daw son, 1973; Flashim oto, 2005) These characteristics have implications for chloroplast protein targeting pathways (A pt et al, 2002; Kilian an d Kroth, 2005) an d possibly for its division m echanism and transm ission to daugh ter cells (Flashim oto, 2005). M any universal core cell cycle genes that regulate these transitions

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