WHEN Elliot Meyerowitz flashes up a slide and says, 鈥淭his is the most
important object on Earth,鈥� you might be in for a surprise. The slide is of an
apical meristem, the structure that caps the extremities of a plant, be they the
highest branches or the deepest roots.
The apical meristem consists of undifferentiated plant stem cells. As new
cells form underneath through division, they specialise, becoming fluid-carrying
xylem or phloem cells, or leaves, or flowers. Our food has its origins in apical
meristems. So do fossil fuels and the oxygen we breathe. 鈥淪o if we like to
breathe, eat and drive a car,鈥� Meyerowitz says, 鈥渨e鈥檇 better find out how the
shoot apical meristem works.鈥�
He and others have already decoded some of the chemical signals plants use to
control their growth and development. Slight changes in these signals can alter
the shape and size of flowers, or even how much pollen or seed they produce.
With a complete repertoire of plant molecular signals, almost anything would be
possible, Meyerowitz says. 鈥淲e can engineer them how we want, provided they鈥檙e
physically capable of doing what we want.鈥�
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Like most plant geneticists, Meyerowitz鈥檚 team does all its work on
Arabidopsis thaliana, a frail weed from the mustard family that is ideal
for research because it is very small, reproduces quickly and is easy to
manipulate through genetic engineering. Using Arabidopsis, he and his
colleagues have discovered how the stem cells in the apical meristem tell the
cells just below them to turn themselves into the pith of a plant鈥檚 vascular
system.
The message consists of a protein鈥攅ncoded by the CLAVATA3
gene鈥攚hich latches onto CLAVATA1, a 鈥渞eceptor kinase鈥� protein that sits
astride the wall of the receiving cell. Through a classic 鈥渓ock and key鈥�
mechanism, CLAVATA1 relays the signal into the receiving cell, priming it to
become part of the pith.
At least a hundred plant receptor kinases such as CLAVATA1 are known to
exist. As yet, little is known about them, except that they are sure to be
important in cell signalling. But Meyerowitz expects progress to accelerate
rapidly this year, after the complete sequence of the Arabidopsis
genome is published.
鈥淲hen it鈥檚 done, we can see how many receptor kinases there are,鈥� says
Meyerowitz. 鈥淎fter that, we can get the sequences and mutate the genes to see
what they do.鈥� He is also confident that the genes in Arabidopsis will
fulfil the same function in all flowering plants, which make up 90 per cent of
land plants and include all major food crops.
Progress is now so rapid that Meyerowitz expects us to have cracked all the
secrets of how plants work within the next century鈥攖hough he鈥檇 prefer it
was done before he retires.
