Zhen-Ming Pei wants to understand how plants sense basic aspects of their environment: salt, temperature and most of all, water. They do this with ion channels, specialized parts of cell membranes that open and close in response to environmental signals. If water is present the corresponding channel stays closed. When the plant lacks water, the channel opens and allows calcium to enter the cell. There the calcium atoms bind to an array of different proteins, triggering many downstream effects.
Identifying the gene responsible requires years of painstaking labor, randomly generating mutant plants and sorting through them to find the ones that don't have the calcium cascade. That would mean that the ion channel is not opening and its controlling gene has mutated. These mutants can be propagated and studied further.
Obviously drought- and salt-resistant crops would have great importance for agriculture. But Zhen-Ming really just wants to work on big questions. The rest of the time he is happy tinkering with his car.