Occurrence of subdioecy and scarcity of gender-specific markers reveal an ongoing transition to dioecy in Himalayan seabuckthorn (Hippophae rhamnoides ssp. turkestanica)

Abstract

Dioecy and the dynamics of its evolution are intensely investigated aspects of plant reproduction. Seabuckthorn (Hippophae rhamnoides ssp. turkestanica) is an alpine shrub growing wild in certain parts of western Himalaya. The previous studies have reported heteromorphic sex chromosomes in the species and yet marker-based studies indicate high similarity between the male and female genomes. Lack of information on sexual system in the species has further complicated the situation. A systematic study was thus undertaken to understand the sexual system in seabuckthorn and to discern the extent of similarity/dissimilarity between the male and female genomes by generating a large number of markers using amplified fragment length polymorphism and representational difference analysis. Floral biology and regular monitoring of species revealed the presence of polygamomonoecious (PGM) plants in most populations at a low percentage (~2-4%). PGM plants showed low pollen production and overall low fertility, suggesting a monoecy-paradioecy pathway at function. The results of the marker study demonstrated that there are limited differences between male and female genomes and these differences were not uniform across the populations in the Leh-Ladakh region, especially when the geographical distance increases. Results also suggest that a dynamic partitioning of genomes is operational between the two genders of seabuckthorn and differences are not homogenized across the populations. Both reproductive biology-based and DNA marker-based studies indicate that genders have separated recently. The present study proposes seabuckthorn as a promising model system to study evolution of dioecy and sex determination.

Variable resource allocation pattern, biased sex-ratio, and extent of sexual dimorphism in subdioecious Hippophae rhamnoides

“…However, we did not find any habitat-influenced bias in such traits of Seabuckthorn. These findings reiterate our previous conclusions of having limited differences between the genomes of sexes in the species, and of the ongoing evolution of dioecy in Seabuckthorn [ 51 ]. Thus, it is likely that sexual dimorphism in the species has recently evolved or ongoing in the species at the site.…”

“…rhamnoides the authors have suggested that 2800 m altitude represents the range for optimal growth of H . rhamnoides ; at higher altitudes water stress induces negative impact on females through poor growth and greater mortality [ 51 ]. Thus, it is likely that the biased sex-ratio may be associated with changing altitude, with SK at the higher elevation (≥300 m), which also conforms with findings in Rumex nivalis [ 28 ].…”

The Systematics, Reproductive Biology, Biochemistry, and Breeding of Sea Buckthorn—A Review

“…A survey of 25 wild populations of H. rhamnoides subsp. turkestanica in northern India showed that 2-4% of the plants were polygamomonoecious (PGM) with male, female, and hermaphrodite flowers, suggesting that the transition from hermaphrodites (the original state for angiosperms) to dioecy (the derived state) happened recently in this genus [38]. Moreover, the male and female genomes appear to be very similar overall.…”

“…A Representational Difference Analysis (RDA) of DNA sequences was applied to the search for gender-specific differences between male and female genomes. Some of the obtained polymorphisms looked promising initially, but none of them held up when screened on plants from more distant populations [38].…”

“…An AFLP analysis conducted on five populations of subsp. turkestanica was more successful and produced 4 female-specific and 2 male-specific fragments that were cloned and sequenced and subsequently used for developing SCAR primers [38]. The genomic region around each SCAR was explored through genome walking, and new primers were designed and then tested on 50 male and 50 female plants.…”