Maturity2, a novel regulator of flowering time in Sorghum bicolor, increases expression of SbPRR37 and SbCO in long days delaying flowering

Sorghum bicolor is a drought-resilient facultative short-day C4 grass that is grown for grain, forage, and biomass. Adaptation of sorghum for grain production in temperate regions resulted in the selection of mutations in Maturity loci (Ma(1) –Ma(6)) that reduced photoperiod sensitivity and resulted in earlier flowering in long days. Prior studies identified the genes associated with Ma(1) (PRR37), Ma(3) (PHYB), Ma(5) (PHYC) and Ma(6) (GHD7) and characterized their role in the flowering time regulatory pathway. The current study focused on understanding the function and identity of Ma(2). Ma(2) delayed flowering in long days by selectively enhancing the expression of SbPRR37 (Ma(1)) and SbCO, genes that co-repress the expression of SbCN12, a source of florigen. Genetic analysis identified epistatic interactions between Ma(2) and Ma(4) and located QTL corresponding to Ma(2) on SBI02 and Ma(4) on SBI10. Positional cloning and whole genome sequencing identified a candidate gene for Ma(2), Sobic.002G302700, which encodes a SET and MYND (SYMD) domain lysine methyltransferase. Eight sorghum genotypes previously identified as recessive for Ma(2) contained the mutated version of Sobic.002G302700 present in 80M (ma(2)) and one additional putative recessive ma(2) allele was identified in diverse sorghum accessions.