Early researchers identified four genes – called Ma1 through Ma4 – that control flowering time in sorghum, Mullet said. Until recently, flowering time regulation was important primarily for grain production. However, the more recent search for alternatives to fossil fuels has led to the development of sorghum as a dedicated bioenergy crop.

“In this study, we identified the gene in sorghum that corresponds to Ma4-1. Mutations in that gene in some sorghum genotypes [deactivate] the gene causing plants to flower early,” Mullet said. “But when the gene is active, the plants flower late. It was a variation in the activity of the gene corresponding to Ma1 that sorghum breeders have been using in breeding programs for years to fine-tune when their hybrids would flower.

“Our work connected the initial discovery of Ma1 in the 1940s to the identification of the gene that was regulating when plants would flower.”

But whether a sorghum plant will flower is not the only catch for using sorghum as a bioenergy crop. Mullet said scientists have long been interested in understanding the fundamental biochemical mechanisms that plants use to determine when to flower.

Researchers in the 1920s and 30s began piecing together the effect of day length, calling it photoperiodism, to describe how a plant decides to turn on its flowering mechanism, Mullet said. More recent research demonstrated that plants use an internal clock to keep track of 24-hour time and light sensory to measure the length of the day and night.

“The interaction of those two types of information is used by the plant to determine when in a growing season to flower,” Mullet said.

“We figured out how the plant’s internal clock and day length in sorghum co-regulate the expression of the Ma1gene called PRR37 to fine-tune exactly when the plant will induce flowering under different circumstances,” Mullet said. “So in a practical sense, we now understand how this gene regulates flowering and this insight is helping us fill in an entire pathway which regulates flowering time in sorghum.”

Murphy indicated that a planting test of sorghum phenotypes with an active form of Ma1 and other genes in this pathway could be delayed in flowering for up to 200 days compared to the usual 60 days for a grain-type sorghum.

“That is a striking difference,” she said, showing two 90-day-old plants, one a non-flowering sorghum plant reaching a 10-foot ceiling and the other a typical 3-foot sorghum variety that would yield grain.

Mullet explained that breeders “can now use molecular markers to assist in the design of sorghum hybrids that flower at optimal times, accelerating the process of breeding high-yielding grain, sweet and energy sorghum hybrids.”