Minor quantitative trait loci underlie floral traits associated with mating system divergence in Mimulus

The genetic basis of species differences provides insight into the mode and tempo of phenotypic divergence. We investigate the genetic basis of floral differences between two closely related plant taxa with highly divergent mating systems, Mimulus guttatus (large-flowered outcrosser) and M. nasutus (small-flowered selfer). We had previously constructed a framework genetic linkage map of the hybrid genome containing 174 markers spanning approximately 1800 cM on 14 linkage groups. In this study, we analyze the genetics of 16 floral, reproductive, and vegetative characters measured in a large segregating M. nasutus x M. guttatus F2 population (N = 526) and in replicates of the parental lines and F1 hybrids. Phenotypic analyses reveal strong genetic correlations among floral traits and epistatic breakdown of male and female fertility traits in the F2 hybrids. We use multitrait composite interval mapping to jointly locate and characterize quantitative trait loci (QTLs) underlying interspecific differences in seven floral traits. We identified 24 floral QTLs, most of which affected multiple traits. The large number of QTLs affecting each trait (mean = 13, range = 11-15) indicates a strikingly polygenic basis for floral divergence in this system. In general, QTL effects are small relative to both interspecific differences and environmental variation within genotypes, ruling out QTLs of major effect as contributors to floral divergence between M. guttatus and M. nasutus. QTLs show no pattern of directional dominance. Floral characters associated with pollinator attraction (corolla width) and self-pollen deposition (stigma-anther distance) share several pleiotropic or linked QTLs, but unshared QTLs may have allowed selfing to evolve independently from flower size. We discuss the polygenic nature of divergence between M. nasutus and M. guttatus in light of theoretical work on the evolution of selfing, genetics of adaptation, and maintenance of variation within populations.     

Morphological and functional characterization of BcMF13 in the antisense-silenced plants of Brassica campestris ssp. chinensis var. parachinensis

The gene Brassica campestris male fertility 13 (BcMF13, GenBank accession number EF158459) was isolated as a reproductive organ-specific gene from Chinese cabbage (Brassica campestris L. ssp. chinensis Makino, syn. B. rapa ssp. chinensis). It is exclusively expressed in stage four and five flower buds of fertile lines and is most strongly expressed in stamens. Here, we report a functional characterization of this BcMF13 gene in the antisense-silenced plants. The inflorescence of the BcMF13 mutant was compacted with anthers curved outside. The fertility of this mutant was greatly reduced with less than 5 seeds per silique. Under scanning electron microscopy, the mutant demonstrated numerous shriveled pollen grains with deep invaginations. The frequency of normal pollen grains was just 45.34%. The pollen mother cell, the tetrad, and the mature pollen of the BcMF13 mutant were abnormal resulting in the poor pollen vitality. Germination test in vivo suggested BcMF13 delayed the pollen tubes’ extension in the style. All these indicated BcMF13 had a vital role in pollen development of Chinese cabbage.     

心叶凹唇姜的开花格局和雄性先熟机制

心叶凹唇姜 (Boesenbergia longiflora) 是分布于亚洲热带的一种姜科植物, 在我国滇南地区成片生长于石灰山贫瘠的岩石缝隙和路边林下的冲积土壤上。心叶凹唇姜的花寿命为两天, 第1天为严格的雄性阶段, 第2天为严格的雌性阶段, 是典型的花内雄性先熟, 一朵花的雌、雄性阶段没有重叠, 因而完全避免了自花授粉的发生。对这两种生境 (石灰山贫瘠的岩石缝隙和路边林下) 下的心叶凹唇姜的4个野外种群 (在云南省普洱市的翠云乡彩虹洞、南岛河、澜沧县惠民乡和西双版纳州绿石林森林公园) 和栽培植株的开花格局进行调查后发现, 大多数个体在同一时间内只有一个花序开花, 并且每隔一天才开一朵花, 只有10%左右的植株同时具有雄性阶段和雌性阶段的花, 这样的开花格局有效地降低了同株异花授粉发生的可能。心叶凹唇姜的平均花粉-胚珠比 (Pollen-ovuleratio) 为291, 应该是以异交为主的混合交配系统。其自然种群存在着花粉限制, 彩虹洞、南岛河和绿石林3个不同种群的平均结籽率都不到60%, 这可能与其较小的花展示有关。心叶凹唇姜为泛化传粉植物, 不同种群的有效传粉昆虫种类各不相同。在两种不同的生境条件下, 心叶凹唇姜花的大小和开花格局都没有显著的差异, 大多数个体同时只具有一种性阶段的花, 说明心叶凹唇姜这种独特的开花格局是长期进化的结果。心叶凹唇姜通过隔一天开一朵花的开花格局, 配合雄性先熟机制, 有效地降低了自交的发生。     

香石竹开花结实生物学研究

通过田间观察,运用TTC法、联苯胺-过氧化氢法、杂交指数、花粉-胚珠比和套袋实验等方法,对香石竹的开花状态及繁育系统进行了研究。结果表明:在人工栽培条件下,香石竹种群可周年开花,单株花期35～61d,单花花期9～15d;花粉在开花第1～5天具有活力,柱头在开花第4～12天具可授性,第8～11天可授性最强;杂交指数为5,P/O值为307.84～790.52,结合坐果率结果,判断其繁育系统属于异交,部分自交亲和,需要传粉者。     

鹅掌柴花蜜腺的发育解剖学研究

对鹅掌柴(Scheffler octophylla Harms．)花蜜腺的发育进行解剖结构观察。鹅掌柴花盘蜜腺位于下位子房上方环绕花柱基部。蜜腺由分泌表皮、产蜜组织组成,心皮维管束与其相邻并发出一些伸入蜜腺基部的短分枝。蜜腺起源于心皮原基基部外侧的几层细胞。鹅掌柴花蜜腺为淀粉型蜜腺,淀粉粒为许多微小颗粒聚集成的复粒。原蜜汁由蜜腺基部维管束的筛管提供,达产蜜组织细胞和表皮细胞后以淀粉粒的形式贮藏。泌出的蜜汁一部分来自淀粉粒的降解,一部分来自泌蜜期输入的原蜜汁。表皮和产蜜组织细胞均具泌蜜功能。泌出的蜜汁大部分通过气孔排出,还有部分由角质层渗出。     

Extreme divergence in floral scent among woodland star species (Lithophragma spp.) pollinated by floral parasites

Backgrounds and Aims

A current challenge in coevolutionary biology is to understand how suites of traits vary as coevolving lineages diverge. Floral scent is often a complex, variable trait that attracts a suite of generalized pollinators, but may be highly specific in plants specialized on attracting coevolved pollinating floral parasites. In this study, floral scent variation was investigated in four species of woodland stars (Lithophragma spp.) that share the same major pollinator (the moth Greya politella, a floral parasite). Three specific hypotheses were tested: (1) sharing the same specific major pollinator favours conservation of floral scent among close relatives; (2) selection favours ‘private channels’ of rare compounds particularly aimed at the specialist pollinator; or (3) selection from rare, less-specialized co-pollinators mitigates the conservation of floral scent and occurrence of private channels.

Methods

Dynamic headspace sampling and solid-phase microextraction were applied to greenhouse-grown plants from a common garden as well as to field samples from natural populations in a series of experiments aiming to disentangle the genetic and environmental basis of floral scent variation.

Key Results

Striking floral scent divergence was discovered among species. Only one of 69 compounds was shared among all four species. Scent variation was largely genetically based, because it was consistent across field and greenhouse treatments, and was not affected by visits from the pollinating floral parasite.

Conclusions

The strong divergence in floral scents among Lithophragma species contrasts with the pattern of conserved floral scent composition found in other plant genera involved in mutualisms with pollinating floral parasites. Unlike some of these other obligate pollination mutualisms, Lithophragma plants in some populations are occasionally visited by generalist pollinators from other insect taxa. This additional complexity may contribute to the diversification in floral scent found among the Lithophragma species pollinated by Greya moths.     

异质生境对二型花柱植物雪地报春花性状分化的影响

该研究以生长在新疆北部的二型花柱植物雪地报春(Primula nivalis)为研究材料,对7个低海拔(1 657~2 013m)森林居群和7个高海拔(2 400~2 700m)草原居群的花型比例进行调查,对花部特征进行检测,并对长、短花柱植株在不同海拔居群的花性状分化进行了比较研究,以揭示该类群植物的演化与环境的关系。结果表明:(1)在高海拔草原居群中长花柱植株比例高于短花柱植株。(2)比较草原和森林生态系统中的雪地报春居群,长花柱花形态特征间存在显著差异,但短花柱花形态特征间的差异不显著。(3)高海拔草原居群中长花柱花的花冠筒长度、雄蕊长度、雌雄蕊距离、雌雄异位程度以及雌雄蕊空间位置是导致花性状分化的主要因素。(4)在草原居群中,长花柱花的雄蕊、雌雄异位程度及花冠口至雄蕊距离的变化减少了长短花柱花间的互补式对应性。研究认为,在异质生境中长花柱花性状的变化是导致该物种长短花柱花性状分化的主要因素。     

Localization of Drug-Metabolizing Enzyme Activities to Blood-Brain Interfaces and Circumventricular Organs

Abstract: The brain, with the exception of the choroid plexuses and Circumventricular organs, is partially protected from the invasion of blood-borne chemicals by the specific morphological properties of the cerebral micro-vessels, namely, the tight junctions of the blood-brain barrier. Recently, several enzymes that are primarily involved in hepatic drug metabolism have been shown to exist in the brain, albeit at relatively low specific activities. In the present study, the hypothesis that these enzymes are located primarily at blood-brain interfaces, where they form an "enzymatic barrier," is tested. By using microdissection techniques or a gradient-centrifugation isolation procedure, the activities of seven drug-metabolizing enzymes in isolated microvessels, choroid plexuses, meningeal membranes, and tissue from three Circumventricular organs (the neural lobe of the hypophysis, pineal gland, and median eminence) were assayed. With two exceptions, the activities of these enzymes were higher in the three Circumventricular organs and cerebral microvessel than in the cortex. Very high membrane-bound epoxide hydrolase and UDP-glucuronosyltransferase activities (approaching those in liver) and somewhat high 7-benzoxyre-sorufin- O -dealkylase and NADPH-cytochrome P-450 reductase activities were determined in the choroid plexuses. The pia-arachnoid membranes, but not the dura matter, displayed drug-metabolizing enzyme activities, notably that of epoxide hydrolase: The drug-metabolizing enzymes located at these nonparenchymal sites may function to protect brain tissue from harmful compounds.     

The gene expression landscape of thermogenic skunk cabbage suggests critical roles for mitochondrial and vacuolar metabolic pathways in the regulation of thermogenesis

Floral thermogenesis has been described in several plant species. Because of the lack of comprehensive gene expression profiles in thermogenic plants, the molecular mechanisms by which floral thermogenesis is regulated remain to be established. We examined the gene expression landscape of skunk cabbage (Symplocarpus renifolius) during thermogenic and post-thermogenic stages and identified expressed sequence tags from different developmental stages of the inflorescences using super serial analysis of gene expression (SuperSAGE). In-depth analysis suggested that cellular respiration and mitochondrial functions are significantly enhanced during the thermogenic stage. In contrast, genes involved in stress responses and protein degradation were significantly up-regulated during post-thermogenic stages. Quantitative comparisons indicated that the expression levels of genes involved in cellular respiration were higher in thermogenic spadices than in Arabidopsis inflorescences. Thermogenesis-associated genes seemed to be expressed abundantly in the peripheral tissues of the spadix. Our results suggest that cellular respiration and mitochondrial metabolism play key roles in heat production during floral thermogenesis. On the other hand, vacuolar cysteine protease and other degradative enzymes seem to accelerate senescence and terminate thermogenesis in the post-thermogenic stage.