The research project started as an exploration of mutations in a sorghum breeding program looking at introducing novel variations to sorghum strains, said Doreen Ware, corresponding author and research scientist with USDA’s Agricultural Research Service.
“It’s a traditional practice in generating new genetic variation to use in breeding programs,” she told FeedNavigator.
The work also offered a way to potentially improve understanding of what regions of a plant’s genome are associated with specific traits by causing specific proteins not to function correctly, she said. “We’re doing some of the more high-risk aspects that can then be more mobilized, and we’re looking at sorghum as a model for other grasses,” she added.
In the specific strain examined in the study, the mutation of interest appeared to make all the flowers on a sorghum stock fertile, she said. Traditionally only about half of the flowers or spikelets on each stem have that ability.
“If you want more seeds you need more fertile flowers,” said Ware. “We can make them all fertile.”
“The normal plant have the flowers, but they do not all maintain fertility,” she said. “When you lose the plant hormone [jasmonic acid] – you have less of the hormone around, you have more flowers that are fertile.”
The process also may be linked to a way to make the plant produce additional flowers, she said. But, in this specific project, the focus was on understanding what controlled the fertility of the flowers.
Research details and results
The research project focused on a series of sorghum mutants that have an increased number of grains produced because all spikelets or flowers are fertile and capable of setting grain, the researchers said. The plant was able to produce normal grain from both sessile and pedicellate spikelets instead of only from sessile spikelets.
From that point, genetic sequencing was used to identify the sorghum gene MSD1 as a Teosinte branched/Cycloidea/PCF (TCP) transcription factor, they said. TCP transcription factors can play several roles in plant development and the project suggested that the gene regulates the activation of genes that make the plant hormone jasmonic acid (JA).
Genome expression profiling revealed that JA enzymes were related to fertility levels in the spikelets, they said. When less of the hormone was present, more flowers or spikelets were fertile and applying the hormone directly to the mutant plants caused a reversion to traditional production.
“In the paper, we were able to show that the genes or the metabolic enzymes that were responsible for making the jasmonic acid expression patterns change,” said Ware.
Implications and future efforts
One implication from the findings is that it could potentially provide a way to increase grain yield in sorghum and several grain crops, the researchers said.
Additional research has been started by research team member Zhanguo Xin, USDA researcher with ARS, to understand the nutritional content of the additional seeds and if the trait is transferable to other sorghum lines, said Ware.
Another implication of the project is the understanding it offers of the hormone pathway involved, she said. “It gives us initial understanding of the biological mechanism,” she added.
“As breeding practices are moving forward in the future, there can be targeted approaches very specifically to track genes to see their impact,” she said. “This is now telling us what hormones are involved in fertility and it may lead to understanding other biological mechanisms as well.”
Additionally, the mutated lines have been made available to some entities involved with reviewing the potential yield improvement the new strain could provide, she said. “Now you have to validate that you’re getting yield increase,” she added.
Source: Nature Communications
Title: MSD1 regulates pedicellate spikelet fertility in sorghum through the jasmonic acid pathway
Authors: Y Jiao, Y Lee, N Gladman, R Chopra, S Christensen, M Regulski, G Burow, C Hayes, J Burke, D Ware, Z Xin