Vivipary is a rare sexual reproduction phenomenon where embryos germinate directly on the maternal plants. However, it is a common genetic event of woody mangroves in the Rhizophoraceae family. The ecological benefits of vivipary in mangroves include the nurturing of seedlings in harsh coastal and saline environments, but the genetic and molecular mechanisms of vivipary remain unclear. Here we investigate the viviparous embryo development and germination processes in mangrove Kandelia obovata by a transcriptomic approach. Many key biological pathways and functional genes were enriched in different tissues and stages, contributing to vivipary. Reduced production of abscisic acid set a non-dormant condition for the embryo to germinate directly. Genes involved in the metabolism of and response to other phytohormones (gibberellic acid, brassinosteroids, cytokinin, and auxin) are expressed precociously in the axis of non-vivipary stages, thus promoting the embryo to grow through the seed coat. Network analysis of these genes identified the central regulatory roles of LEC1 and FUS3, which maintain embryo identity in Arabidopsis. Moreover, photosynthesis related pathways were significantly up-regulated in viviparous embryos, and substance transporter genes were highly expressed in the seed coat, suggesting a partial self-provision and maternal nursing. We conclude that the viviparous phenomenon is a combinatorial result of precocious loss of dormancy and enhanced germination potential during viviparous seed development. These results shed light on the relationship between seed development and germination, where the continual growth of the embryo replaces a biphasic phenomenon until a mature propagule is established.

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Quantifying the strength of the ecogeographic barrier is an important aspect of plant speciation research, and serves as a practical step to understanding the evolutionary trajectory of plants under climate change. Here, we quantified the extent of ecogeographic isolation in four closely related Aquilegia species that radiated in the Mountains of SW China and adjacent regions, often lacking intrinsic barriers. We used environmental niche models to predict past, present, and future species potential distributions and compared them to determine the degree of overlap and ecogeographic isolation. Our investigation found significant ecological differentiation in all studied species pairs except A. kansuensis and A. ecalacarata. The current strengths of ecogeographic isolation are above 0.5 in most cases. Compared with current climates, most species had an expanding range in the Last Glacial Maximum, the Mid Holocene, and under four future climate scenarios. Our results suggested that ecogeographic isolation contributes to the diversification and maintenance of Aquilegia species in the Mountains of northern and SW China and would act as an essential reproductive barrier in the future.

Water-saving, drought-resistant rice (WDR) (Oryza sativa L.) is a type of new rice cultivars with high drought resistance and low water consumption in the production phase. Ratoon rice cropping is regarded as a resource-efficient rice production system with low cost and high profit. The development of ratoon rice system with WDR is conducive to the sustainable production of rice and the expansion of rice plantation; however, no such attempt has been made. In this study, a field experiment was conducted for 2 yr to evaluate the feasibility of developing new ratoon rice cropping systems using WDR compared with using common lowland rice (CLR). The productivity, regenerative capacity, and water use efficiency (WUE) were investigated in the water-saving cultivation system using two WDR cultivars-Jieyou 652 and Jieyou 804-and in the conventional flooding cultivation system using the CLR cultivar Fengliangyouxiang 1. The irrigation WUE for the WDR systems was 89.8-214.8% and 243.4-765.6% higher than for the CLR system in the main and ratoon cropping seasons, respectively. The grain yield was not significantly different in the main cropping season between the WDR and CLR systems; nevertheless, it was lower in the WDR systems because of shorter growth duration and smaller panicles in the ratoon season. Higher accumulations of dry matter (DM), nonstructural carbohydrates (NSCs), and nitrogen in the stubble of main-season crops is helpful to the promotion of regenerative capacity of WDR in the ratoon season. INTRODUCTIONRice (Oryza sativa L.) is one of the most important grain crops in the world because it feeds more than half of the global population as staple food (Seck et al., 2012). China is the largest Abbreviations: CLR, common lowland rice; D2, second node from the uppermost of main-season plants; D3, third node from the uppermost of main-season plants; D4, fourth and below nodes from the uppermost of main-season plants; DM, dry matter; IWUE, irrigation water use efficiency; NSC, nonstructural carbohydrate; TWUE, total water use efficiency; WDR, water-saving, drought-resistant rice; WUE, water use efficiency.