Presence/absence of a CACTA transposon in the CYC2c gene of two genotypes of Helianthus × multiflorus cv. “Meteor” characterized by a radiate inflorescence with different shape of disk flower corollas

Abstract

Helianthus × multiflorus is a triploid (2n = 51) interspecific hybrid derived from the cross of H. decapetalus with H. annuus that exists in radiate and ligulate inflorescence types. The H. × multiflorus “Soleil d’Or” has a ligulate inflorescence, with actinomorphic corolla of disk flowers converted in zygomorphic ray-like corollas. In “Soleil d’Or”, a truncated CACTA transposable element (TE), named CTEHM1, is integrated in the HmCYC2c gene, a key player controlling zygomorphism in the Helianthus genus. Here, we showed that H. × multiflorus “Meteor”, originated from a mutation of “Soleil d’Or”, exists in two different types of radiate inflorescence, here named “Meteor 1” and “Meteor 2”. Notably, in “Meteor 1”, which displayed a corolla of disk flowers typical for the Helianthus genus, CTEHM1 was transposed from the HmCYC2c gene. In contrast, the CTEHM1 TE was still present in the HmCYC2c gene of “Meteor 2”. In this genotype, the largest corolla of the disk flowers shows some features of the ray flowers giving rise to a radiate inflorescence unusual for the Helianthus genus. The in silico analysis of CTEHM1 also highlights the presence of a 202 bp CpNpG island, which is a putative target of methylation. Interestingly, the gene expression of the HmCYC2c gene was significantly higher in disk flowers of “Meteor 2” compared to “Meteor 1”. Stated these results, we suggest that both the excision of a TE and an epigenetic regulation of gene expression generate the two-inflorescence types of H. × multiflorus, “Meteor 1” and “Meteor 2”.