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As a postdoc at the University of California, Berkeley, in the mid-1980s, Rob Martienssen discovered a mutation in maize plants that caused their leaves to have a very pale green color. Cells carrying this mutation don’t develop chloroplasts, and as a result, the plants couldn’t perform photosynthesis. Seedlings would survive for only a week or two on stored nutrients before perishing. “This mutant had a very strong lethal phenotype,” Martienssen says. “But from time to time it reverted,” he adds. “And it reverted in a very striking way.”
Some of his mutant corn plants began to grow striped leaves, with bands of healthy dark-green tissue interspersed with the pale-green cells, and those plants survived a little longer. “From one leaf to the next, you would ...
