Location: Wheat, Sorghum and Forage Research
Project Number: 3042-21220-034-001-I
Project Type: Interagency Reimbursable Agreement
Start Date: Sep 1, 2020
End Date: Aug 31, 2024
Sorghum is being developed as a bioenergy feedstock for the U.S. However, the use of genetic engineering to improve sorghum for this emerging market is restricted due to the risk of gene flow to two endemic related weed species, Johnson grass, (Sorghum halepense) and shattercane (Sorghum bicolor ssp. drummondii) with which sorghum is sexually compatible. In the U.S., grain sorghum is also being marketed as “non-GMO” grain for export and gluten-free foods, which is likely a greater gene flow risk. Therefore, preventing both pollen flow and seed set in genetically engineered sorghum are critical containment barriers required for safe use of genetic engineering advances in bioenergy and forage sorghums. The goal is to develop a sorghum line(s) that when crossed to genetically engineered sorghum, the resultant progeny will not produce pollen or seeds under temperate conditions. To address this goal, ARS will identify and characterize cytoplasmic male sterile lines to prevent pollen flow in the resultant progeny, lines that delay or prevent flowering under a temperate photoperiod in the resultant progeny, and evaluate the two combined containment strategies in regulated field trials.
The sorghum parental line ‘RTx430’ is the most widely used line for sorghum transformation. Our goal is to identify existing sorghum germplasm that when pollinated by RTx430, the resultant progeny will not either produce pollen or flower under temperate field conditions. Combining these two traits together will provide redundancy and further reduce the risk of gene flow to other sorghum and weedy relatives. To prevent pollen development, two cytoplasmic male sterility systems, A3 and A5 will be evaluated. Seed set in these lines will be evaluated under both field and greenhouse conditions to determine fertility rate and risk of pollen flow. To prevent/delay flowering during the temperate growing season, sorghum with a complementary set of Maturity (Ma) genes to the ones in RTx430 will be evaluated. Sorghum is a short-day flowering plant, and recessive loss-of-function Ma alleles at the six Ma loci increase photoperiod insensitivity under long days. The resultant progeny from the RTx430 cross will have five or six functional Ma alleles at Ma1 -- Ma6 loci, which will confirm photoperiod sensitivity and delay flowering. Timing of flowering in these lines will be evaluated under both field and greenhouse conditions to determine days to anthesis and associated risks. Marker assisted breeding will be used to combine cytoplasmic male sterility with the complementary set of Ma alleles in a single line, which will be tested with genetically engineered sorghum to evaluate efficacy under an APHIS permit in the field.