Biology subjects

Zeeman, S.

Publications and source records attributed to Zeeman, S..

2 recordsLinked to original sources

bioRxiv2020

Two distinct phases of chloroplast biogenesis during de-etiolation in Arabidopsis thaliana

Light triggers chloroplast differentiation whereby the etioplast transforms into a photosynthesizing chloroplast and the thylakoid rapidly emerges. However, the sequence of events during chloroplast differentiation remains poorly understood. Using Serial Block Face Scanning Electron Microscopy (SBF-SEM), we generated a series of chloroplast 3D reconstructions during differentiation, revealing chloroplast number and volume and the extent of envelope and thylakoid membrane surfaces. Furthermore, we used quantitative lipid and whole proteome data to complement the (ultra)structural data, providing a time-resolved, multi-dimensional description of chloroplast differentiation. This showed two distinct phases of chloroplast biogenesis: an initial photosynthesis-enabling Structure Establishment Phase followed by a Chloroplast Proliferation Phase during cell expansion. Moreover, these data detail thylakoid membrane expansion during de-etiolation at the seedling level and the relative contribution and differential regulation of proteins and lipids at each developmental stage. Altogether, we establish a roadmap for chloroplast differentiation, a critical process for plant photoautotrophic growth and survival.

plant biology↗

bioRxiv2020

Disruption of glycogen metabolism alters cell size in Escherichia coli

The availability of nutrients impacts cell size and growth rate in many organisms. Research in E. coli has traditionally focused on the influence of exogenous nutrient sources on cell size through their effect on growth and cell cycle progression. Utilising a set of mutants where three genes involved in glycogen degradation - glycogen phosphorylase (glgP), glycogen debranching enzyme (glgX) and maltodextrin phosphorylase (malP) - were disrupted, we examined if endogenous polyglucan degradation affects cell size. It was found that mutations to malP increased cell lengths and resulted in substantial heterogeneity of cell size. This was most apparent during exponential growth and the phenotype was unaccompanied by alterations in Z-ring occurrence, cellular FtsZ levels and generation times. {Delta}malP mutant cells did, however, accumulate increased DnaA amounts at late growth stages indicating a potential effect on DNA replication. Replication run-out experiments demonstrated that this was indeed the case, and that DNA replication was also affected in the other mutants. Bacteria with a disruption in glgX accumulated glycogen and protein inclusion bodies that coincided with each other at inter-nucleoid and polar regions.

microbiology↗