The phytochrome gene family in tomato (Solanum lycopersicum L.)
Phytochrome apoproteins in angiosperms are encoded by a small gene family. Tomato (Solatium lycopersicum L.) serves well as a dicotyledonous model system for elucidating the extent of this gene family, its expression patterns, and the roles of individual members of the family. Five phytochrome genes (PHYA, PHYB1, PHYB2, PHYE and PHYF have been characterized in tomato. Quantitative measurements of transcript abundances from each tomato PHY throughout the life cycle indicate that transcript levels generally range from 10 to 100 μmol mol−1 total mRNA, in the following order of decreasing abundance: PHYA, PHYB1, PHYE, PHYB2 and PHYF. PHYA transcripts were found to be most abundant in seedling roots, while PHYB2 and PHYF transcripts were expressed preferentially in fruit. PHYA mutants (fri) have been found to be the consequence of a single nucleotide substitution adjacent to the 3′ terminus of an intron. What are almost certainly PHYB1 mutants have also been described, although the molecular nature of these mutants remains to be revealed. Efforts to obtain PHYB2, PHYE and PHYF mutants are currently underway.