Abstract
Sorghum is an important C4 grass crop grown for grain, forage, sugar, and bioenergy production. While tall, late flowering landraces are commonly grown in Africa, short early flowering varieties were selected in US grain sorghum breeding programs to reduce lodging and to facilitate machine harvesting. Four loci have been identified that affect stem length (Dw1-Dw4). Subsequent research showed that Dw3 encodes an ABCB1 auxin transporter and Dw1 encodes a highly conserved protein involved in the regulation of cell proliferation. In this study, Dw2 was identified by fine-mapping and further confirmed by sequencing the Dw2 alleles in Dwarf Yellow Milo and Double Dwarf Yellow Milo, the progenitor genotypes where the recessive allele of dw2 originated. The Dw2 locus was determined to correspond to Sobic.006G067700, a gene that encodes a protein kinase that is homologous to KIPK, a member of the AGCVIII subgroup of the AGC protein kinase family in Arabidopsis.
Highlights
Plant height is determined primarily by the length and number of stem internodes
Comparison of Dwarf Yellow Milo (DYM) and Double Dwarf Yellow Milo (DDYM) stem internode lengths at anthesis showed that the recessive allele of dw[2] in DDYM caused a reduction in the length of every elongated internode compared to the corresponding internodes in DYM (Supplementary Fig. S1)
The dw[2] allele found in DDYM was used extensively in U.S grain sorghum breeding programs and the Sorghum Conversion Program[19] to reduce the length of stems of sorghum genotypes such as IS3620c and BTx642 that were used in this study to clone Dw2
Summary
Plant height is determined primarily by the length and number of stem internodes. The number of internodes produced by a plant is a consequence of growth duration and the rate of internode production. Dw3 encodes a homolog of the maize Br2 gene and is an ATP-binding cassette type B1 (ABCB1) auxin efflux transporter. The gene corresponding to Dw1 was recently identified as Sobic.009G229800 by map-based cloning[16, 17]. This gene regulates internode cell proliferation[17] and encodes a putative membrane protein not previously assigned a function[16]. The dw[1] allele originating from Dwarf Yellow Milo has been used extensively in grain sorghum breeding programs. Recessive alleles of Ma1 and the dwarfing genes were used in the Sorghum Conversion Program to convert tall late flowering landraces from Africa into short, early flowering genotypes that are useful for grain sorghum breeding. Dw2 was identified as a protein kinase whose closest homolog in Arabidopsis is the kinesin-like calmodulin-binding protein (KCBP)-interacting protein kinase (KIPK), a member of the AGCVIII subfamily that includes PINOID (PID) and PHOTOTROPIN1 and 2 (PHOT1 and 2)
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