C(35)-apocarotenoids in the yellow mutant Neurospora crassa YLO

The Neurospora crassa mutant YLO exhibits a yellow phenotype instead of the red-orange pigmentation of the wild type. Recently, it was shown that the mutant YLO is defective in a specific aldehyde dehydrogenase which catalyses the last step of carotenogenesis to the formation of neurosporaxanthin [Estrada, A.F., Youssar, L., Scherzinger, D., Al-Babili, S., Avalos, J., 2008. The ylo-1 gene encodes an aldehyde dehydrogenase responsible for the last reaction in the Neurospora carotenoid pathway. Mol. Microbiol. 69, 1207-1220]. Since different carotenoid compositions between wild type and YLO have been reported in earlier publications, the carotenoids of YLO were analyzed and unknown carotenoids identified. Fractionation of carotenoid extracts from YLO revealed in the less polar fraction two major carotenoids of low polarity which were found only in trace amounts in the wild type. Both carotenoids could be hydrolyzed with KOH to more polar products indicating the presence of fatty acid esters. The fatty acid moiety was identified as myristic acid by gas chromatography. Optical and mass spectra as well as co-chromatography with a synthesized authentic standard identified the free alcohols as 4'-apolycopene-4'-ol and 4'-apo-gamma-carotene-4'-ol which assigns the dominating carotenoids in the YLO mutant as 4'-apolycopene-4'-myristate and 4'-apo-gamma-carotene-4'-myristate. We can attribute the accumulation of these two carotenoids in YLO to the substantial mutation of the neurosporaxanthin-forming aldehyde dehydrogenase. However, the aldehyde intermediates 4'-apo-gamma-carotene-4'-al and 4'-apo-lycopene-4'-al do not accumulate substantially but are reduced instead to the corresponding alcohols, 4'-apolycopene-4'-ol and 4'-apo-gamma-carotene-4'-ol, and both further esterified with mainly myristic acid yielding 4'-apolycopene-4'-myristate and 4'-apo-gamma-carotene-4'-myristate.