Study of a wild species closely related to asparagus by Kazusa DNA Research Institute and collaborators: Decoding the genome of Asparagus kiusianus

Kazusa DNA Research Institute, Kagawa Prefectural Agricultural Experiment Station and the Graduate School of Life Sciences of Tohoku University have jointly decoded the genome of Asparagus kiusianus, a wild species closely related to asparagus. As the wild species is resistant to stem blight, and there is cross-compatibility between this wild species and asparagus, DNA markers can be developed for the breeding of interspecific hybrid varieties of asparagus with stem blight resistance and stress resistance. It can also contribute to the evolutionary research of speciation, such as the mechanism by which interspecific crosses are established. This research was published online in DNA Research.

Garden asparagus is a perennial monocot (single embryonic leaf) native to the Mediterranean region that can be harvested for more than a decade when planted and has a high market value. It can be cultivated in small plots and is suitable for house cultivation, which is less susceptible to climate. Although there are many cultivars of garden asparagus, those bred to date have been grown from only a few native lines and so are poor in genetic diversity. In recent years, studies on cultivar breeding using asparagus and other hybridizable wild species (belonging to the genus Asparagus) have been conducted in multiple countries.

Four closely related species of asparagus are known in Japan, among which the most notable is Asparagus kiusianus. It grows naturally on the sandy beaches of northern Kyushu and Yamaguchi Prefecture and has been declared endangered (Ministry of the Environment Red List Category IB: Endangered). Since it inhabits sandy beaches, it is expected to have a range of stress tolerances, such as salt tolerance and drought tolerance, but stem blight resistance is its most notable trait. Asparagus stem blight is a disease caused by a mold. The development of stem blight resistance varieties is crucial because the control of the disease becomes difficult after it has been contracted. However, there is no cultivar with stem blight resistance in garden asparagus.

With this background in mind, in the Agriculture R&D Innovation Promotion Program that the Kagawa Prefectural Agricultural Experiment Station and Tohoku University are participating in, the researchers are promoting the cultivation of stem blight-resistant varieties using Asparagus kiusianus. It is also important to study the genome of Asparagus kiusianus not only in terms of the use of genetic resources but also in terms of protection of endangered species. The possibility of hybridization between the two species indicates that there is a risk of gene contamination of Asparagus kiusianus with garden asparagus DNA.

Genome information on Asparagus kiusianus will be an effective tool for genome checking, which is the basis for regulation of the cultivation of edible asparagus and interspecific hybrids near native habitats. It is believed that the asparagus family diverged from other monocotyledonous (single embryonic leaf) plants earlier than rice, immediately after the divergence of eudicots (two embryonic leaves) and monocotyledons during evolution. Therefore, it retains its status as an early monocotyledon. In addition, it substantially contributes to exploring the early evolution of monocots from their genomes.

Asparagus kiusianus and garden asparagus are dioecious strains, but there are some species of wild asparagus that are hermaphrodites. This genome analysis is expected to help shed light on the history and evolution of male and female acquisition in asparagus. Since Asparagus kiusianus is dioecious, the collaborative research group has decoded the genomes of the male and female strains, each of which has 1.6 billion base pairs and approximately 55,000 identified genes. Differences in genome structure and different DNA sequences between male and female strains were revealed. The group also found the male specific sex-determining genes MSE1/AoMYB35/AspTDF1 of asparagus from the genome of the male lineage of Asparagus kiusianus. The investigation and comparison of the whole-genome structure of asparagus and Asparagus kiusianus has shed some light on the molecular mechanism of stem blight resistance.