1a.Objectives (from AD-416):
Examine effects of specific modifications to lignin biosynthesis through bmr loci or transgenic over expression on feeding of green bugs (phloem feeder) corn earworms and fall armyworms (chewing insects). Examine the effects of these lignin modifications on the colonization of fungi causing foliar or stalk diseases, anthracnose, stalk rot, and charcoal rot. In the relevant lines, investigate the potential underlying mechanisms for significantly reduced insect feeding or fungal colonization relative to wild-type.
1b.Approach (from AD-416):
The 4 bmr loci and transgenic over expression of 4 genes involved in monolignol biosynthesis will be used to manipulate lignin. The bmr loci all result in reduced lignin content, but have distinct effects on lignin composition and phenylpropanoid metabolism. The genes encoding enzymes in monolignol biosynthesis at critical branch points will be over expressed, as well as a putative transcriptional regulator of lignin biosythesis. Resistance to fungal pathogens will be assessed in the field and through greenhouse inoculation with fungal isolates containing GFP to examine fungal growth and extent of fungal penetration. Insect feeding studies will be performed using isolated leaves from staged plants at a fixed position. Phenolicin metabolites will be analyzed by GC-MS in lines exhibiting fungal or insect resistance. Global gene expression will be analyzed using a newly developed Agilent sorghum genome microarray.
Sorghum lines with different natural variations in lignin composition and resistance chemical profile were evaluated for resistance against two insect pests of the grass family. Some significant differences in resistance to feeding were noted. In a few cases younger altered lignin plants had more feeding damage than normal lignin plants. In most cases, the leaves from older altered lignin plants had less damage by caterpillars than normal plants. Stalk pith of both low lignin lines was significantly more toxic to the caterpillars than pith from normal plants. Results in the first year of field tests were similar to those noted under controlled conditions.