Identifying the sex-determining gene in the dioecious plant, white campion: Fukui Prefectural University and others clarify development pathway

A research group consisting of Professor Yusuke Kazama of the Faculty of Bioscience and Biotechnology, Fukui Prefectural University, Specially Appointed Researcher Shigeyuki Kawano of the Graduate School of Frontier Sciences, The University of Tokyo (Emeritus Professor of the University of Tokyo), Tomoko Abe, Director of the Beam Mutagenesis Group, RIKEN Nishina Center for Accelerator-Based Science and their colleagues has, together with Kyoto University and the University of Oxford in the UK, succeeded in identifying the sex-determining gene (GSFY) which located in the Y chromosome and controls the formation of pistils of white campion, a dioecious plant (has either male or female flowers, but not both).

Since the Y chromosome of plants was first discovered in 1923, researchers around the world have searched for the sex-determining gene that exists in white campion chromosomes. However, these chromosomes have a large number of repeated sequences - 10 times those of a human Y chromosome - so it was extremely difficult to identify the sex-determining gene from among them.

The research group induced mutations in Y chromosomes by irradiating a heavy ion beam on white campion, and produced 11 mutant lineages with bisexual flowers that have both pistils and stamens. The group carried out whole genome sequencing and RNA-seq (sequence analysis focusing on RNA) on these 11 lineages and extracted a gene that existed only in the male flowers, rather than in the female or bisexual flowers, leading them to discover the gene in the Y chromosome that controls the development of pistils (GSFY).

The protein encoded by the GSFY gene has high homology with the CLV3 gene in the model organism, thale cress. CLV3 is a small peptide made up of 12 amino acids, and its role is to reduce the size of the meristem. In fact, when the group applied GSFY peptide to female white campion flower buds, the meristem was reduced in size and pistil development was suppressed.

A gene (GSFX) with an extremely similar sequence to GSFY also existed in the X chromosome, but a mutation appeared in a key amino acid in its peptide, and its function was lost. Based on this, it is conceivable that the similar genes GSFY and GSFX were common in both X and Y chromosomes, but there was genetic dysfunction in the evolutionary process of GSFX in the X chromosome, and so GSFY particular to the Y chromosome started to function as the male-determining gene.

Kawano commented, "We have identified the sex-determining gene that controls pistil development for the first time through an experiment in which we treated female flowers with a peptide made up from the 12 amino acids included in this gene. We also found a gene that develops pistils in the X chromosome. From now on, we hope to use this to clarify the evolution of the sex chromosome during the evolution of dioecious plants from bisexual plants, which has been a major question since Darwin."

Journal Information
Publication: Molecular Biology and Evolution
Title: A CLAVATA3-like Gene Acts as a Gynoecium Suppression Function in White Campion
DOI: 10.1093/molbev/msac195