Abstract
Simple SummaryRice water weevil (RWW), Lissorhoptrus oryzophilus (Kuschel) (Coleoptera: Brachyceridae), is one of the main pests of rice. In 1959, the parthenogenetic RWW was first reported in California and invaded Asia in 1978. It is known that sexually reproducing RWW is a diploid organism, while parthenogenetic RWW is a triploid organism and its distribution range is much larger than in sexually reproducing populations. We provide valuable molecular evidence for parthenogenesis and analyze the cellular basic process of parthenogenetic RWW. Results show in particular that the parthenogenetic RWW has chromosome unipolar division during meiosis, Tws (a regulatory subunit of protein phosphatase 2A) has low expression in ovarian tissue, and REC8 (paralogous gene of Verthandi/Rad21) is normally expressed. Our study indicates that parthenogenetic RWW produces triploid egg cells via chromosome unipolar division, while low expression of Tws within ovarian tissues may be associated with parthenogenesis, thus providing the first molecular genetic evidence for the parthenogenetic RWW.Rice water weevil (RWW) is divided into two types of population, triploid parthenogenesis and diploid bisexual reproduction. In this study, we explored the meiosis of triploid parthenogenesis RWW (Shangzhuang Town, Haidian District, Beijing, China) by marking the chromosomes and microtubules of parthenogenetic RWW oocytes via immunostaining. The immunostaining results show that there is a canonical meiotic spindle formed in the triploid parthenogenetic RWW oocytes, but chromosomes segregate at only one pole, which means that there is a chromosomal unipolar division during the oogenesis of the parthenogenetic RWW. Furthermore, we cloned the conserved sequences of parthenogenetic RWW REC8 and Tws, and designed primers based on the parthenogenetic RWW sequence to detect expression patterns by quantitative PCR (Q-PCR). Q-PCR results indicate that the expression of REC8 and Tws in ovarian tissue of bisexual Drosophila melanogaster is 0.98 and 10,000.00 times parthenogenetic RWW, respectively (p < 0.01). The results show that Tws had low expression in parthenogenetic RWW ovarian tissue, and REC8 was expressed normally. Our study suggests that the chromosomal unipolar division and deletion of Tws may cause parthenogenesis in RWW.
Highlights
Parthenogenesis is a reproductive mode in which female animals produce offspring from unfertilized eggs [1]
Rice water weevil (RWW) has a telotrophic type ovary; we dissected the ovary of parthenogenetic RWW and individual ovarian tube tissues were immunostained for microtubules and chromosomes
The meiotic process of parthenogenetic RWW (Figure 2) involves unipolar segregation of all chromosomes during anaphase I followed by a traditional meiotic second division leading to the production of triploid eggs
Summary
Parthenogenesis is a reproductive mode in which female animals produce offspring from unfertilized eggs [1]. Bisexual RWWs only exist in North America [9], while the parthenogenetic form is widely distributed in various countries, showing stronger environmental adaptability and invasive ability [10]. Previous studies have distinguished the chromosome ploidy of RWW between bisexual reproduction and parthenogenesis (2 n = 22 and 3 n = 33, respectively) [6,11], and suggested that both chromosome polyploidization and parthenogenesis could increase the environmental adaptability and invasiveness of organisms [12,13]. We studied the meiotic process, the expression pattern of REC8 (a paralogous gene of Verthandi/Rad in insects, connecting homologous chromatid to maintain synaptic complex structures) and Tws (encoding a regulatory subunit of protein phosphatase 2A) gene in parthenogenetic RWW ovarian tissues, providing important insight for further study of the cellular and molecular mechanisms in parthenogenetic organisms
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