The Arabidopsis nox Mutant Lacking Carotene Hydroxylase Activity Reveals a Critical Role for Xanthophylls in Photosystem I Biogenesis  

Abstract

Carotenes, and their oxygenated derivatives xanthophylls, are essential components of the photosynthetic apparatus. They contribute to the assembly of photosynthetic complexes and participate in light absorption and chloroplast photoprotection. Here, we studied the role of xanthophylls, as distinct from that of carotenes, by characterizing a no xanthophylls (nox) mutant of Arabidopsis thaliana, which was obtained by combining mutations targeting the four carotenoid hydroxylase genes. nox plants retained a-and b-carotenes but were devoid in xanthophylls. The phenotype included depletion of light-harvesting complex (LHC) subunits and impairment of nonphotochemical quenching, two effects consistent with the location of xanthophylls in photosystem II antenna, but also a decreased efficiency of photosynthetic electron transfer, photosensitivity, and lethality in soil. Biochemical analysis revealed that the nox mutant was specifically depleted in photosystem I function due to a severe deficiency in PsaA/B subunits. While the stationary level of psaA/B transcripts showed no major differences between genotypes, the stability of newly synthesized PsaA/B proteins was decreased and translation of psaA/B mRNA was impaired in nox with respect to wild-type plants. We conclude that xanthophylls, besides their role in photoprotection and LHC assembly, are also needed for photosystem I core translation and stability, thus making these compounds indispensable for autotrophic growth.

Bilin-Dependent Photoacclimation in Chlamydomonas reinhardtii

“…Alternatively, this decrease may be due to the altered synthesis or integration of specific xanthophylls. This latter possibility, though not addressed in this manuscript, has been demonstrated for the Arabidopsis nox mutant that lacks xanthophylls and accumulates almost no PSI (Dall'Osto et al, 2013). The nox mutant lacks LHCII polypeptides and accumulates very little LHCI polypeptides, but unlike the Chlamydomonas hmox1 mutant, it does accumulate an appreciable amount of LHCA2 (Dall'Osto et al, 2013).…”

“…This latter possibility, though not addressed in this manuscript, has been demonstrated for the Arabidopsis nox mutant that lacks xanthophylls and accumulates almost no PSI (Dall'Osto et al, 2013). The nox mutant lacks LHCII polypeptides and accumulates very little LHCI polypeptides, but unlike the Chlamydomonas hmox1 mutant, it does accumulate an appreciable amount of LHCA2 (Dall'Osto et al, 2013). Regardless of the distribution of chlorophyll a and chlorophyll b in the mutant, the failure of hmox1 cells to green reflects their inability to accumulate new PSI complexes in the light that apparently arises from an aberrant bilin-dependent posttranscriptional process that is light mediated.…”

Regulation of Carotenoid Metabolism in Tomato

“…Oxidative stress in tomato fruit increases coordinately with fruit ripening and reaches a peak at the final stages, which facilitate metabolic changes and fruit softening (Jimenez et al, 2002). High amounts of liposoluble antioxidant compounds, such as lycopene and b-carotene, accumulate to protect the photosystems and fruit cells (Dall'Osto et al, 2013). It should be possible to improve the fruit nutrients by enhancing fruit plastids (chloroplasts and chromoplasts) at different stages of fruit development, as well as balancing light absorption and redox protection (Cocaliadis et al, 2014).…”

Carotenoid responses to environmental stimuli: integrating redox and carbon controls into a fruit model

“…In addition to their role in photoprotection and light harvesting complex (LHC) assembly, xanthophylls have been found to play an essential role in PSI core translation and stability (Dall'Osto et al 2013). The authors suggest the possibility of a signal from carotenoids or carotenoid catabolites that can affect the molecular mechanisms underlying PSI assembly.…”