Expression of the defense gene mir1 depends on herbivore feeding guild and maize genotype

Abstract: Maize is attacked in the field by three different feeding guilds of herbivores that include chewing, sucking and root feeding pests. The inbred, Mp708 appears to have resistance to each of these feeding guilds. Previous work has demonstrated its resistance to fall armyworm (FAW, Spodoptera frugiperda) and western corn rootworm (WCR, Diabrotica virgifera virgifera) and recently we have discovered that it is also resistant to the corn leaf aphid (CLA, Rhopalosiphum maidis). Our results have shown that transcripts for mir1, the gene encoding the cysteine protease Mir1-CP which is toxic to caterpillars, accumulate within 1 hr post CLA feeding. Preliminary results suggest that jasmonic acid (JA) and ethylene (ET) regulate mir1 expression in response to FAW whereas ET alone regulates mir1 expression in response to CLA. Work is underway to determine if western corn rootworm (WCR, Diabrotica virgifera virgifera) also affects mir1 expression. Since the inbred Mp708 was developed from maize landraces that originated from Central America, we speculate that the parental landrace was selected because of its ability to resist herbivory in an area of high insect pressure and propose that the capacity to express mir1 may have been lost during the modern breeding process. To test this we are studying the ability of a diverse group of maize genotypes to accumulate mir1 transcripts in response to herbivory.