Induced point mutations in the phytoene synthase 1 gene cause differences in carotenoid content during tomato fruit ripening |
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Authors: | Antoine L F Gady Wim H Vriezen Marion H B J Van de Wal Pingping Huang Arnaud G Bovy Richard G F Visser Christian W B Bachem |
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Institution: | (1) Laboratory of Plant Breeding, Department of Plant Sciences, Wageningen-UR, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands;(2) Nunhems Netherlands BV, P.O. Box 4005, 6080 AA Haelen, The Netherlands;(3) Graduate School Experimental Plant Sciences, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands;(4) Present address: Laboratory of Genetics, Department of Plant Sciences, Wageningen-UR, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands |
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Abstract: | In tomato, carotenoids are important with regard to major breeding traits such as fruit colour and human health. The enzyme
phytoene synthase (PSY1) directs metabolic flux towards carotenoid synthesis. Through TILLING (Targeting Induced Local Lesions
IN Genomes), we have identified two point mutations in the Psy1 gene. The first mutation is a knockout allele (W180*) and the second mutation leads to an amino acid substitution (P192L).
Plants carrying the Psy1 knockout allele show fruit with a yellow flesh colour similar to the r, r mutant, with no further change in colour during ripening. In the line with P192L substitution, fruit remain yellow until
3 days post-breaker and eventually turn red. Metabolite profiling verified the absence of carotenoids in the W180* line and
thereby confirms that PSY1 is the only enzyme introducing substrate into the carotenoid pathway in ripening fruit. More subtle
effects on carotenoid accumulation were observed in the P192L line with a delay in lycopene and β-carotene accumulation clearly
linked to a very slow synthesis of phytoene. The observation of lutein degradation with ripening in both lines showed that
lutein and its precursors are still synthesised in ripening fruit. Gene expression analysis of key genes involved in carotenoid
biosynthesis revealed that expression levels of genes in the pathway are not feedback-regulated by low levels or absence of
carotenoid compounds. Furthermore, protein secondary structure modelling indicated that the P192L mutation affects PSY1 activity
through misfolding, leading to the low phytoene accumulation. |
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