Embryological and genetic evidence of amphimixis and apomixis in Boehmeria tricuspis

Abstract

Apomixis is a widespread alternative mode of sexual reproduction resulting in offspring that are genetically identical to the maternal plant. Boehmeria tricuspis (Hance) Makino is a perennial, wind-pollinated, herbaceous plant in the nettle family Urticaceae. The diploid B. tricuspis is monoecious but the triploid B. tricuspis is gynoecious, bearing female inflorescences only. Apomixis in B. tricuspis was first reported 50 years ago, but the mode of apomixis in the species has not been described yet. Here, we provide embryological observations of the embryo sac formation proving that triploid B. tricuspis reproduced apomictically following the Antennaria type of diplospory, and that the diploid individuals were the sexual genotype with the classical Polygonum-type maturation pattern of embryo sac development. A subsequent flow cytometry seed screen (FCSS) showed that the triploids were obligate apomicts with autonomous endosperm development, and the diploids reproduced sexually. In addition, a progeny test by molecular marker assays further demonstrated the above results.

A Full-Length Reference Floral Transcriptome ofBoehmeria tricuspisProvides Insights into Apomeiosis and Polyploidy

“…Plant Material and RNA Extraction. Two cytotypes of B. tricuspis previously reported [24,25] were used in this work: the sexual cytotype "JG1" (2n = 2x = 28) and the full apomictic cytotype "ZJJ" (2n = 3x = 42). JG2 and HD were collected from Hubei Province and Zhejiang Province of China, respectively, and the ploidy levels were measured by chromosome counting in root tips as proposed by Bennett and Smith [38].…”

“…The four natural cytotypes were planted in the experimental field of the Institute of Bast Fiber Crops, Chinese Academy of Agricultural Sciences, Changsha, Hunan, China. With providing the cytoembryological observation of sexual and apomictic individuals of B. tricuspis [25], a calendar of the reproductive development was established (Table S1). The MMC developmental stage could be estimated by the outer appearance of the flowers.…”

“…B. tricuspis exhibits numerous characteristics such as simple growth requirements and high seed yield that render it both an excellent and intriguing system for the study of apomixis. In a prior research, we identified that the B. tricuspis triploid cytotype reproduces through obligate diplosporous apomixis, whereas diploids appeared to be a fully sexual cytotype [25]. Notably, at the functional megaspore-formed stage, in sexual ovules, the megaspore mother cell (MMC) produces four megaspores through meiosis, and one of the megaspores is selected to become a functional megaspore while the other ones degenerate, whereas in diplosporous ovules, MMC directly develops into a functional megaspore without the meiotic and degenerative process.…”

“…Reads from cytotype JG2 and HD at the functional megaspore-formed stage were produced in this study. The data from cytotype JG1 and ZJJ at the functional megaspore-formed stage were derived from a previous study [25]. The trimmed reads of each cytotype were separately realigned to the high-quality reference transcriptome.…”

Apomictic development during different flower development stages in Crataegus tanacetifolia (Lam.) Pers., endemic to Turkey

“…Apomixis is the ability of a plant to pass through the essential steps (meiosis and fertilization) of the sexual reproduction to produce fertile seeds (Tang et al, 2016;Hojsgaard and Hörald, 2019). It is divided into 3 subtypes based on the origin of embryo-forming cells i.e.…”