Characterization of phytoene synthases from cassava and their involvement in abiotic stress-mediated responses

https://v2.sherpa.ac.uk/id/publication/8158 Published Version OA Publishing: This pathway includes Open Access publishing Embargo: No Embargo Licence: CC BY Location: Any Website Institutional Repository Named Repository (PubMed Central) Subject Repository Journal WebsiteAbiotic stress stimuli induce the increased synthesis of abscisic acid (ABA), which is generated through the cleavage of xanthophyll precursors. To cope with the increased xanthophyll demand, maize and rice contain a third stress-induced gene copy, coding for phytoene synthase (PSY), which catalyzes the first carotenoid-specific reaction in the pathway. To investigate whether this specific response extends beyond the Poaceae, cassava was analyzed, an important tropical crop known for its drought tolerance. We also found three PSY genes in cassava, one of which (MePSY3) forms a separate branch with the stress-specific Poaceae homologs. However, MePSY3 transcripts were virtually absent in all tissues investigated and did not change upon abiotic stress treatment. In contrast, the two remaining PSY genes contributed differentially to carotenoid biosynthesis in leaves, roots, and flower organs and responded towards drought and salt-stress conditions. Detailed analyses of PSY and 9-cis-epoxycarotenoid cleavage dioxygenase (MeNCED) expression and resulting ABA levels revealed MePSY1 as the main stress-responsive paralog. In the presence of high carotenoid levels in leaves, MePSY1 appeared to support, but not to be rate-limiting for ABA formation; MeNCED represented the main driver. The inverse situation was found in roots where carotenoid levels are low. Moreover, ABA formation and the relative induction kinetics showed discrimination between drought and salt stress. Compared to rice as a drought-intolerant species, the drought response in cassava followed a different kinetic regime. The difference is thought to represent a component contributing to the large differences in the adaptation towards water supply

Carotenoid crystal formation in Arabidopsis and carrot roots caused by increased phytoene synthase protein levels

As the first pathway-specific enzyme in carotenoid biosynthesis, phytoene synthase (PSY) is a prime regulatory target. This includes a number of biotechnological approaches that have successfully increased the carotenoid content in agronomically relevant non-green plant tissues through tissue-specific PSY overexpression. We investigated the differential effects of constitutive AtPSY overexpression in green and non-green cells of transgenic Arabidopsis lines. This revealed striking similarities to the situation found in orange carrot roots with respect to carotenoid amounts and sequestration mechanism

Altered Dark- and Photoconversion of Phytochrome B Mediate Extreme Light Sensitivity and Loss of Photoreversibility of the phyB-401 Mutant

The phyB-401 mutant is 103 fold more sensitive to red light than its wild-type analogue and shows loss of photoreversibility of hypocotyl growth inhibition. The phyB-401 photoreceptor displays normal spectral properties and shows almost no dark reversion when expressed in yeast cells. To gain insight into the molecular mechanism underlying this complex phenotype, we generated transgenic lines expressing the mutant and wild-type phyB in phyB-9 background. Analysis of these transgenic lines demonstrated that the mutant photoreceptor displays a reduced rate of dark-reversion but normal Pfr to Pr photoconversion in vivo and shows an altered pattern of association/dissociation with nuclear bodies compared to wild-type phyB. In addition we show (i) an enhanced responsiveness to far-red light for hypocotyl growth inhibition and CAB2 expression and (ii) that far-red light mediated photoreversibility of red light induced responses, including inhibition of hypocotyl growth, formation of nuclear bodies and induction of CAB2 expression is reduced in these transgenic lines. We hypothesize that the incomplete photoreversibility of signalling is due to the fact that far-red light induced photoconversion of the chromophore is at least partially uncoupled from the Pfr to Pr conformation change of the protein. It follows that the phyB-401 photoreceptor retains a Pfr-like structure (Pr*) for a few hours after the far-red light treatment. The greatly reduced rate of dark reversion and the formation of a biologically active Pr* conformer satisfactorily explain the complex phenotype of the phyB-401 mutant and suggest that amino acid residues surrounding the position 564 G play an important role in fine-tuning phyB signalling

Re:site montréal

"Felix S. Huber and Philip Pocock joined together in July 1995 to go up to the Arctic Ocean in the Northwest of Canada by camper van. While travelling through its physical remoteness, they created arctic circle, a “travel-as-art-as-information” project and simultaneous travelogue on the internet1. Every other day they dialed from private homes into THE THING’s2 newly installed ftp server and uploaded buckets of web pages containing text exchanges and performance loops in Quicktime format." -- p. [5