One can plainly see that maize plants produce very few lateral branches at their base. The sparseness of tillers, as these branches are called by plant biologists, is the first clue: plants with many lateral branches don't tend to grow well in close proximity, for their branches and leaves tend to throw any close neighbors into shade, thus limiting access to sunlight, their common prime energy source. By severely limiting its lateral branching, maize is able to redirect its energy to the primary shoot, which grows taller and escapes the shade.
"It is actually human selection that has done this," explains Jackson. "Although maize plants produce tiller buds, the nascent branches fail to grow out, which results in the plant's familiar dominant central stalk." The team knew that maize plants in which gt1 is mutated generate several tillers and additional ear branches; this suggested that gt1 expression is normally associated with the suppression of tiller growth. This was confirmed in tests in which gt1 expression was measured in plants grown in the laboratory equivalent of shade.
Another maize gene called teosinte branched1, or tb1, is also known to regulate tiller bud growth and lateral branching in maize, and to be active in response to internal signals indicating the presence of shade. The next question was whether the two genes act in a common pathway, or separately. The expression of each was measured when the other was experimentally inactivated. "We found that gt1 doesn't get activated unless tb1 i
|Contact: Peter Tarr|
Cold Spring Harbor Laboratory