Definition: In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.
Input: Article: Like people, plants experience stress. And also, like people, the response to that stress can determine success.  Bad environmental conditions, such as drought, flood, heat and other stresses, affect yields  more than crop pests and diseases. We are trying to find a way to equip plants with the ability to tolerate environmental stress and maintain high yields, said Stephen Howell, a professor of genetics and cell biology. Plant cells produce proteins   and ship them to different parts of the cell. Under normal conditions, these proteins are folded into their normal, healthy structures as they are produced. When a plant is under stress, its cells produce poorly folded or unfolded proteins. Then a built-in system senses this and "sets off an alarm in the cell," said Howell. In response to the alarm, another protein (IRE1) starts working and creates a different process which activates   the stress response genes whose products bring about defensive measures that help the plant survive. "As it turns out, responses that are activated under stress conditions actually inhibit the growth of plants," said Howell. "This allows them to preserve their energy to survive the stress conditions."     For plants in the wild, this response is a help for survival, he said. In production of agriculture crops, however, this response reduces yields. "You don't want crop plants to stop growing," Howell said. "You want them to continue to grow and produce even though they are under stress." With the new understanding of this stress response, the next step may be to silence the alarm system, said Howell. "What may be important is to disable some of these stress responses. That may make the plant more productive under stress conditions." 
 Answer: the changed proteins

According to the text, an alarm in the plant cells is caused by   _  .