Phytoene accumulation in sunflower decreases the transcript levels of the phytoene synthase gene

The non dormant-1 (nd-1) mutant of sunflower (Helianthus annuus L.) and fluridone-treated plants were used to investigate the effect of phytoene accumulation on the transcript levels of the phytoene synthase (Ha-PSY) gene. A deficiency at the gene coding for zeta-carotene desaturase (ZDS) characterises the nd-1 mutant, which displays an accumulation of zeta-carotene, phytofluene and cis-phytoene and the absence of beta-carotene and xanthophylls. The transcript levels of Ha-PSY, in concomitance with phytoene accumulation, decreased (1.9-fold) in fluridone-treated wild-type seedlings with respect to untreated leaves. Phytoene-accumulating cotyledons of nd-1 seedlings also displayed a 2.9-fold decrease of Ha-PSY mRNA levels in comparison with the control samples. To exclude that the reduced transcript levels of Ha-PSY was dependent by a decrease of the total carotenoid content another pigment-deficient mutant, named xantha1 (xan1), was used. The xan1 mutant has a normal carotenoid complement but photodestruction of both chlorophyll a and beta-carotene directly correlate with light intensity. The increase of Ha-PSY mRNA, in normal-pigmented cotyledons, was concurrent with the enhanced light intensity. The same up-regulation for Ha-PSY was observed in xan1, irrespective of the drastic reduction of the total carotenoid content displayed by mutant seedlings grown under high light intensity. Taken together, our data suggest that in H. annuus the steady state levels of Ha-PSY mRNA was negatively affects by phytoene accumulation but not by a decrease in total carotenoid content.