Mutations in the TCP Transcription Factor MSD1 Modify Flower and Panicle Development in Sorghum

Sorghum is an important global food, forage, and bioenergy crop with an annual production value of over two billion dollars in the USA. This C4 photosynthetic grass has resilience to heat, drought, low soil fertility, and other abiotic and biotic stresses that have made it an agricultural mainstay across geographic and socioeconomic boundaries. Sorghum flowers are comprised of one fertile (sessile) and two sterile (pedicillate) spikelets, with only the sessile spikelet producing seed. Through an EMS mutagenesis screen, our group identified several independent mutations in the TCP transcription factor gene MSD1 (multiseed) that results in the complete fertility of all sessile and pedicillate spikelets. Additionally, msd1 panicles are larger, have increased primary and secondary branches, and produce more seed than wild type panicles. Recently, we have begun to dissect the molecular mechanism for this agronomically significant phenotype and have shown that the majority of msd1 alleles, which non-synonymously impact the DNA-binding domain, result in the heritable multiseed trait. Further, MSD1 has a narrow temporal- and tissue-specific expression profile and it physically interacts with other TCP proteins in planta. These data taken together suggest that i) MSD1 may be involved in a complex regulatory schema to control proper sorghum panicle development, and ii) the multiseed trait is a candidate for integration into sorghum breeding programs for the purpose of increasing grain yield and enhancing global agricultural security.