Unravelling key regulators of spikelet determinacy in barley

• Applicant: Ravi Koppolu, Ph.D.
• Subject Area: Plant Breeding and Plant Pathology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 521774690

Ever since the dawn of agriculture, cereal grains have become the prime source of nutrition for humankind. Both barley and wheat are among the top cereal grain crops cultivated across the globe. Grains in barley, wheat, and other cereals are produced in specialized flower-bearing structures called spikelets. Cereals encompass an amazing source of variation for the spikelet architecture. One such variation is the number of florets (grass flowers that ultimately become grains) produced per spikelet. The barley spikelets bear a single floret; however, wheat spikelets generate more florets per spikelet (often up to four grain bearing florets). Such crucial floret number differences in these crops are manifested by the growth activity or arrest of the spikelet organ called “rachilla”. In the determinate barley spikelets, the rachilla ceases to grow upon initiation of the first floret, whereas in the indeterminate wheat spikelets rachilla growth continues to produce more florets per spikelet making it an important grain yield-determining organ in these crops. Despite its importance, very little is known so far about the genetic and molecular mechanisms driving the rachilla initiation, growth, and arrest processes. Previously, I have characterized a barley indeterminate spikelet mutant, multiflorus 2.b (mul2.b) that quantitatively enhanced rachilla growth and the number of grain-bearing florets per spikelet (up to three). Extensive phenotypic and genetic analyses of barley mul2.b uncovered two major quantitative trait loci (QTL) controlling rachilla growth and floret formation. With the knowledge in this research area and available genetic resources, in the current research proposal, i aim to (i) identify the genes underlying the two major rachilla growth/floret formation QTLs in mul2.b by map-based cloning, and (ii) functional characterization of these genes through allele mining, CRISPR/Cas9 based genome editing, and targeted rachilla transcriptome profiling in mul2.b. The genes underlying the barley mul2.b QTLs and their allelic variation, provide an essential genetic tool kit for breeders aiming to improve grain yield in barley and potentially other cereal crops. On the other hand, the targeted rachilla transcriptome studies in mul2.b offer first insights into molecular regulation underlying rachilla development in barley. Altogether, these findings will provide a comprehensive overview of rachilla development and floret formation in barley, and probably other cereals; which can be leveraged to improve grain yields of these crops in the future.

• DFG Programme: Research Grants