Diverse chalcone synthase superfamily enzymes from the most primitive vascular plant, Psilotum nudum

AbstractFlavonoids are important polyphenolic natural products, ubiquitous in land plants, that play diverse functions in plants’ survival in their ecological niches, including UV protection, pigmentation for attracting pollinators, symbiotic nitrogen fixation, and defense against herbivores. Chalcone synthase (CHS) catalyzes the first committed step in plant flavonoid biosynthesis and is highly conserved in all land plants. In several previously reported crystal structures of flowering plant CHSs, the catalytic cysteine is oxidized to sulfinic acid, indicating enhanced nucleophilicity in this residue associated with its increased susceptibility to oxidation. In this study, we report a set of new crystal structures of CHSs representing all five major lineages of land plants. We reveal that the structures of CHS from a lycophyte and a moss species preserve the catalytic cysteine in a reduced state, in contrast to the cysteine sulfinic acid seen in all euphyllophyte CHS structures. In vivo complementation, in vitro biochemical and mutagenesis analyses, as well as molecular dynamics simulations identify a set of residues that differ between basal-plant and euphyllophyte CHSs and modulate catalytic cysteine reactivity. We propose that the CHS active-site environment has evolved in euphyllophytes to further enhance the nucleophilicity of the catalytic cysteine since the divergence of euphyllophytes from other vascular plant lineages 400 million years ago. These changes in CHS could have contributed to the diversification of flavonoid biosynthesis in euphyllophytes, which in turn contributed to their dominance in terrestrial ecosystems.

Download Full-text

The Occurrence of Polycomplexes During the Sporogenesis in Psilotum Nudum

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s1431927600002348 ◽

1980 ◽

Vol 38 ◽

pp. 532-533

Author(s):

Kit W. Lee

Keyword(s):

Developmental Stages ◽

Higher Plants ◽

Vascular Plant ◽

Uranyl Acetate ◽

Late Zygotene ◽

Synaptonemal Complexes ◽

Chromosome Synapsis ◽

Psilotum Nudum ◽

Consistent Feature ◽

Ethanol Series

The structure of the polycomplexes has been extensively studied in recent years (1,2,3). Theres structures are usually described as stacks or aggregates of the tripartite synaptonemal complexes. Although the presence of the synaptonemal complexes is a consistent feature in the late zygotene or pachytene stages of chlasmate meiosis and Its role in the processes of chromosome synapsis and crossing over has been suggested (4), the function of the polycomplexes remains obscure. Most of our understandings of the polycomplexes are obtained from the observations during the gametogenesis of the insects, and only a few examples of this structure in fungi and higher plants have been reported. The present study examines the occurrence of polycomplexes during the sporogenesis in the primitive vascular plant. Sporangia at different developmental stages were fixed with 3% glutaraldehyde in 0.1 M phosphate buffer, and postflxed in 2% osmium tetroxide. Dehydration was carried out with the ethanol series followed by embedding in Epon 812. Ultrathln sections were stained with uranyl acetate and lead citrate.

Download Full-text