Sunflower ‘Sunspot’ is Hyposensitive to GA3 and has a Missense Mutation in the DELLA Motif of HaDella1

Gibberellins (GAs) are phytohormones that regulate plant height and flowering time in plants. Plants with reduced GA or disrupted in GA signaling exhibit a dwarf phenotype. DELLA proteins are transcriptional repressors that attenuate GA-mediated promotion of plant growth. Alleles in which the eponymous DELLA motif in these proteins is disrupted result in constitutive repression of GA signaling and a dominantly inherited dwarf phenotype. We found that the dwarf Helianthus annuus (sunflower) cultivar Sunspot is hyposensitive to GA 3 as compared with the tall cultivar Mammoth Grey. Sequencing of the HaDella1 gene indicates that ‘Sunspot’ has a single nucleotide polymorphism resulting in a missense mutation in the DELLA motif as compared with ‘Mammoth Grey’ and the reference sequence. Helianthus annuus has five genes encoding DELLA proteins, including HaDella1 . We propose that the DELLA motif alteration in the HaDella1 gene results in a dominant mutation in ‘Sunspot’ and is the cause of its dwarf phenotype.