As I watch this year’s impatiens, vinca and petunias shrivel up and die, this is what I am not
thinking: “oh goodie, I get to plant another crop of annuals next
spring!” No, I am thinking, “if a stupid tulip can be a perennial, why
can’t these come back every year, too, with minimal intervention on my
part?”
I am therefore looking forward to plant breeders taking a discovery published online this afternoon in Nature Genetics and later in a print version
of the journal and putting it to widespread use. The discovery is that
by turning off a mere two genes (out of some 25,000) in the little
flowering annual called thale cress (Arabidopsis thaliana), scientists managed to turn it into a perennial.
Annuals, of
course, germinate, grow, blossom and die within one growing season.
Perennials overwinter and grow again the following year, thanks to
buds, bulbs or tubers that contain groups of non-specialized cells
(called meristems) that can differentiate into new organs such as
stalks and leaves. Annuals lack these overwintering meristems. Instead,
they consume all the meristems during the growing season to produce
flowers: once the flower appears, the end is nigh for an annual.
Arabidopsis thaliana has become a favorite of geneticists. The complete sequence of its genome was finished in December 2000, so scientists led by Siegbert Melzer and Tom Beeckman of the Flanders Institute for Biotechnology in Ghent, Belgium, exploited that knowledge to the full. They identified two flower-inducing genes (with the less-than-melodious names SUPPRESSOR
OF OVEREXPRESSION OF CONSTANS 1 and FRUITFULL; I am not yelling at you,
but names of genes are, by convention, capitalized). Both genes also
affect whether the meristems differentiate. Using standard techniques,
the scientists turned off the two genes and watched what happened.
The mutant Arabidopsis
plants couldn’t flower, which is what you’d expect when their
flower-making genes are knocked out of commission. But the more
tantalizing finding is that the mutants do not use up their supply of
non-specialized cells—the meristem. As a consequence, they are able to
grow like perennials. The resulting plants were woodier and more
shrub-like than regular Arabidopsis. (A natural mutation such
as this may well account for the evolution of herbaceous, i.e.
non-woody, annuals to woody perennials, namely shrubs and trees.) As
the scientists write, disabling the two genes produced plants with“recurrent growth cycles, longevity and extensive woodiness, . . . reminiscent of plants with a perennial life style.”
I call first dibs when the geniuses at Spring Hill, Burpee
or other plant nursery or breeder put this discovery to use by giving
us perennial pansies, petunias, marigolds, zinnias and all the rest.
Then when I see the autumnal decline of my garden, I’ll console myself
with the knowledge that they’ll all be back in the spring with little
to no help from me.