IPK researchers provide insights into the mechanism of determining grain number in barley

Modifying inflorescences with higher grain capacity is crucial for grain production. A recurring goal is to select bud sites with more branching or floral structures. Prominent examples include genes affecting floral identity or meristem determination, for which natural or induced variants radically alter floral primordial number. However, in temperate grain crops such as wheat and barley, excessive floral structures can result in a degeneration penalty due to the indeterminate nature of meristems. On the other hand, the manifestation of this reproductive potential can be enhanced by environmental variations such as light, temperature, and diet. Increasing the proportion of surviving flowers/spikelets can thus improve grain yield in cereals.

Now, IPK researchers have unveiled a previously unrecognized mechanism by which signals in the barley inflorescence vasculature control plastid differentiation and nutrient signaling, thereby maintaining heterotrophic floral meristem growth and reproductive success. Their results demonstrate that the circadian clock of the vasculature is required for a timely transition from the initial state of flowering to the state of growth.

Through large-scale dissection of floral meristems and phenotyping, the researchers show that about 40% of initiated floral primordia seed grains, while the rest are aborted, representing untapped yield potential. “We further show that the number of primordial buds initiated is largely determined by flowering-time genes, but the fate of the distal bud sites is controlled by at least three independent quantitative trait loci,” says Dr. Yongyu Huang, first author of the study.

“We have a vascularly expressed one for the first time CCT motif family gene (HvCMF4), which is required for spikelet rudiment growth and successful pollination,” says Dr. Yongyu Huang. Furthermore, the research team showed that HvCMF4 works specifically after initiation of spikelet rudiments by wiring the circadian clock from the inflorescence vessels to drive greening of adjacent tissues; and thus autotrophic energy production. “This mechanism for determining grain number has not been described before and appears to be unique Triticeae Species showing early greening of inflorescences during spikelet initiation and differentiation.”

“Our study reveals a new way to increase grain yield and demonstrates the possibility of increasing the number of grains not only by obtaining more bud sites, but also by transporting them to maturity,” says Prof. Dr. Thorsten Schnurbusch, head of the IPK research group “Plant Architecture” and professor for developmental genetics of useful plants at the Martin Luther University in Halle. “Since barley is one of the most important grain crops in the world (number four after rice, corn and wheat), better utilization of its grain yield potential can thus contribute to world food security and thereby directly contribute to combating the threats of hunger caused by climate change, natural or war disasters .”