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 by ARS Crop Bioprotection Research Unit scientists at the National Center for Agricultural Utilization Research (NCAUR), Peoria, Illinois for resistance against two insect pests of the grass family. An additional mutant line was evaluated under controlled conditions, and leaf damage was either not significantly different (small plants) or had enhanced resistance (large plants) compared to normal lignin plant leaves. Results in the second year of small plot tests were similar to those noted the prior year, and indicated no substantial problems for the low lignin lines. Large scale field studies indicated similar results to laboratory and small plot studies, with significantly reduced leaf damage in one of the low lignin lines, as well as reduced stalk boring damage by insects. Initial evaluation of transgenic plants overexpressing two lignin-biosynthesis associated proteins indicated in most cases the enhanced lignin plants had reduced caterpillar feeding damage compared to normal lignin plants.