last modified Aug. 24, 1999
Plant P450s in Gymnosperms show some plant P450 familes are ancient.
A search of the Pinus ESTs from the EST database identifies 23 ESTs. Only one of these may be questionable from the extreme C-terminal. The other 22 belong to 9 distinct sequences. These include the known sequences 73A20 and 78A4 as well as 7 new sequences. For a list and alignments see Pine P450s.
The evolutionary importance of these sequences is that they show the CYP85 clan, the CYP86 clan and several families like CYP73, CYP78, CYP98 and probably CYP77 and CYP90 predate the divergence of gymnosperms and angiosperms. This divergence is thought to be at least 360 million years (1).
Since green plants evolved from a single celled ancestor about 1 billion years ago, they have proliferated their P450 families from a presumed CYP51 to the present day 45 families. It is not known how many families existed before gymnosperms and angiosperms diverged. At least 5 families have not been found in Arabidopsis so far (80, 92, 99, 703 and 719). The 80 and 719 families are only seen in Ranunculales, and they may be unique P450s to this group of plants. 92 is in monocots and dicots, so it should be found in Arabidopsis also. 99 is seen only in Sorghum, but it is very close to 71D and so it may be a fringe member of this larger group that is seen in many eudicots. 703 is only known from petunia. Until Arabidopsis is done and rice has been sequenced, it is premature to say if any of these families are absent from these model monocot and dicot species. If they are not found in these two genomes, then it may be possible to say they represent new families specific to a narrow range of the angiospems.
As more ESTs accumulate from pine, the question of how many P450 families predate the angiosperm gymnosperm divergence will become answerable. My guess is that most P450 familes existed before the gymnosperm angiosperm split. At least the major P450 clans in plants were present by that time. The extensive diversity in flower color and secondary metabolite biochemistry has probably been accomplished by recruitment of existing P450s to new tasks, without the need to evolve new P450 families.
1) Troitsky AV, Melekhovets YuF, Rakhimova GM, Bobrova VK, Valiejo-Roman KM, Antonov ASAngiosperm origin and early stages of seed plant evolution deducedfrom rRNA sequence comparisons.J. Mol. Evol. 32, 253-61 (1991).