Natural hybridization between Phyllagathis and Sporoxeia species produces a hybrid without reproductive organs

Natural hybridization plays important roles in plant evolution and speciation. In this study, we sequenced ribosomal internal transcribed spacer (nrITS), four low-copy nuclear genes (Dbr1, SOS4a, SOS4b and PCRF1) and the chloroplast intergenic spacer trnV-trnM to test the hypothesis of hybridization between two species of Phyllagathis and Sporoxeia (Sonerileae/Dissochaeteae, Melastomataceae). Our results provided compelling evidence for the hybridization hypothesis. All hybrid individuals sampled were first-generation hybrids. The failure of flower production in the F1 hybrid individuals may work as the barrier preventing later-generation hybridization or backcross. Analysis of the chloroplast trnV-trnM sequences showed that the hybridization is bidirectional with S. petelotii as the major maternal parent. Several factors, such as sympatry, similar habitat preference, overlapping flowering season and shared pollinators, might have contributed to this hybridization event. The "intergeneric" hybridization reported in this study suggests close relationship between P. longicalcarata and S. petelotii.

自然杂交在植物演化与物种形成过程中发挥着关键作用。本研究通过对核核糖体内部转录间隔区（nrITS）、4个低拷贝核基因（Dbr1、SOS4a、SOS4b及PCRF1）以及叶绿体基因间隔区trnV-trnM进行测序，以验证锦香草属（Phyllagathis）与肉穗野牡丹属（Sporoxeia）两个类群（野牡丹科Melastomataceae，蜂斗草族/野海棠族Sonerileae/Dissochaeteae）间存在杂交的假说。本研究结果为该杂交假说提供了强有力的支撑证据。所有采样得到的杂交个体均为第一代杂交种（F1）。F1杂交个体无法开花，这可能构成了阻碍后续世代杂交或回交的生殖隔离屏障。对叶绿体trnV-trnM序列的分析表明，本次杂交为双向杂交，其中肉穗野牡丹（Sporoxeia petelotii）为主要母本。同域分布、生境偏好相似、花期重叠以及共享传粉者等多个因素，可能共同促成了本次杂交事件的发生。本研究报道的“属间”杂交现象，表明长萼锦香草（Phyllagathis longicalcarata）与肉穗野牡丹（Sporoxeia petelotii）之间存在较近的亲缘关系。