Chromosome Unipolar Division and Low Expression of Tws May Cause Parthenogenesis of Rice Water Weevil (Lissorhoptrus oryzophilus Kuschel)

SIMPLE SUMMARY: Rice 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. ABSTRACT: 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.