It appears that hp-1 and hp-2 are mutations in two different transcription factors that each control expression of various light regulated genes. Transcription factors are regulatory genes often controlling a cascade of related genes in one or more biochemical pathways. The "high pigment" naturally occuring mutants hp-1 and hp-2 (and their various alleles) are characterized by an exagerated light responsiveness, darker green foliage, and increased fruit pigmentation. The increased fruit pigmentation is the result of increased accumulation or carotenoid pigments (primarily lycopene). Interestingly there is also an inceased level of production and accumulation of various other beneficial phytochemicals, including vitamins C and E. This led Levin et. al. (2003) to state that these characteristics make one or more of these hp genes/alleles attractive candidates for non-GE "functional" tomatoes. The term "functional foods" is now being used to describe foods with enhanced nutritional quality. A recent paper in Nature stirred some controversy reporting the production of GE tomatoes with transcription factors from Snapdragon that up-regulated anthocyanin production. Anthocyanin and carotene are common plant pigments, both now associated with various potential health benefits.
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