Genetic regulation of self‐incompatibility

Self‐incompatibility is a cell‐cell recognition system in higher plants that is based on the ability of the pistil to discriminate “self‐pollen from “non‐self"‐pollen. In the simplest systems, this recognition response is controlled by a single locus — the S‐locus — with multiple alleles. Pollination of a pistil with pollen bearing an S‐allele recognition factor identical to that expressed in the host plant stigma or style results in rejection of the “self"‐pollen. Most of the studies on the molecular genetics of self‐incompatibility that are summarized in this review have had as their goal the identification and characterization of the gene product(s) associated with the self‐incompatibility response. These studies have provided a great deal of new and important information about self‐incompatibility — despite the fact that many critical questions remain unresolved. Taken together, the present evidence from these studies indicates that the self‐incompatibility response is likely to be far more complex than suggested by historical models.     

Prezygotic barriers to gene flow between <Emphasis Type="Italic">Taraxacum ceratophorum</Emphasis> and the invasive <Emphasis Type="Italic">Taraxacum officinale</Emphasis> (Asteraceae)

Prezygotic reproductive barriers limit interspecific gene flow between congeners. Here, I examine the strength of floral isolation and interspecific pollen-pistil barriers between an invasive apomictic, Taraxacum officinale, and the indigenous sexual alpine dandelion, Taraxacum ceratophorum. Experimental arrays of either native inflorescences or a mixture of native and exotic inflorescences were used to examine insect preference and to track movement of a pollen analog. Using hand-pollinations, conspecific and heterospecific pollen germination success on native stigmas was compared. To additionally test for interspecific pollen competition, T. ceratophorum plants received one of three possible hand-pollinations: control conspecific pollination, concomitant conspecific and heterospecific pollination (mixed), or conspecific pollen followed by heterospecific pollen 15 min later (staggered). Floral isolation was negligible as no insect preference was detected. On a presence/absence basis, florets on native inflorescences received slightly less pollen analog from heterospecific donors than from conspecific donors; however, the amount of dye particles transferred from either Taraxacum species to stigmas on recipient T. ceratophorum inflorescences was equivalent. In contrast to weak floral isolation, strong pollen germination and pollen competition barriers should reduce the potential for hybridization. Heterospecific T. officinale pollen exhibited reduced germination success on T. ceratophorum stigmas in comparison to conspecific pollen. Furthermore, a significant pollen-competition effect on the percentage of hybrid offspring was detected only when T. officinale preceded T. ceratophorum pollen by 15 min. This result indicates that conspecific pollen out-competes heterospecific pollen but further suggests that biotic and abiotic factors reducing pollen accrual rates may partially remove barriers to natural hybridization.     

小麦三雌蕊性状的遗传分析与连锁标记开发

CH257是‘三粒小麦’与普通小麦‘石优20’回交3次后选育的一个三雌蕊材料,可大幅度增加小麦的穗粒数。为了解析小麦三雌蕊性状的遗传方式,挖掘其控制基因并开发相关分子标记,该研究利用CH257和‘中国春’配制组合,获得其F₁、F₂和BC₁F₁群体进行遗传分析;使用纯合正常和纯合三雌蕊F₂株系,采用分离群体分组分析法(bulked segrgant analysis,BSA)构建单雌蕊、三雌蕊混池进行90K基因芯片扫描,根据芯片结果在相应区段开发分子标记。结果表明：CH257中三雌蕊的发育受1对显性单基因Pis CH257控制;使用90K基因芯片扫描将Pis CH257定位于2DL染色体上,在2DL相应区段开发标记,共获得5个与Pis CH257连锁的共显性SSR标记,其顺序为2DL07、2DL17、2DL22、Pis CH257、2DL25、2DL38,Pis CH257两侧的连锁标记2DL22、2DL25与其遗传距离分别为1.1cM和2.5cM。本研究结果为克隆控制小麦三雌蕊性状的基因奠定了基础。     

Strength, diversity and plasticity of postmating reproductive barriers between two hybridizing oak species (Quercus robur L. and Quercus petraea (Matt) Liebl.)

Very little is known about the nature and strength of reproductive isolation (RI) in Quercus species, despite extensive research on the estimation and evolutionary significance of hybridization rates. We characterized postmating pre- and postzygotic RI between two hybridizing oak species, Quercus robur and Quercus petraea, using a large set of controlled crosses between different genotypes. Various traits potentially associated with reproductive barriers were quantified at several life history stages, from pollen-pistil interactions to seed set and progeny fitness-related traits. Results indicate strong intrinsic postmating prezygotic barriers, with significant barriers also at the postzygotic level, but relatively weaker extrinsic barriers on early hybrid fitness measures assessed in controlled conditions. Using general linear modelling of common garden data with clonal replicates, we showed that most traits exhibited important genotypic differences, as well as different levels of sensitivity to micro-environmental heterogeneity. These new findings suggest a large potential genetic diversity and plasticity of reproductive barriers and are confronted with hybridization evidence in these oak species.     

Circadian autonomy and rhythmic precision of the Arabidopsis female reproductive organ

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二倍体普通荞麦异常花朵及其结构的研究

在二倍体普通荞麦BW1 9 1的自交后代群体中有一些植株上的很多花朵形态及其结构发生变异。对这些异常花朵的形态进行了观察 ,统计了各变异花朵的被片数目 (x1)、花柱数目 (x2 )、胚珠数目 (x3 )和雄蕊数目 (x4)等参数。结果发现 ,该群体植株的花朵类型多达 2 5种以上。同一植株上花朵的被片数目 (x1)、花柱数目 (x2 )、胚珠数目 (x3 )和雄蕊数目 (x4)等参数变异广泛。大多数花朵为 5被片 3花柱 1胚珠 8雄蕊 ,但是被片数变幅为 3～ 8,雄蕊数变幅为 3～ 1 1 ,花柱数变幅为 2～ 8,胚珠数变幅为 1～ 3。当花柱数分别为 2、3、4、5、6、7或 8时 ,胚珠数分别是 1 (正常 )、1 (正常 )、1 (正常 ) +0 (未发育胚珠 )、1 (正常 ) +1 (小型胚珠 )、2 (正常 )、2 (正常) +0 (未发育胚珠 )或 2 (正常 ) +1 (小型胚珠 )。偏相关分析表明 ,被片数与花柱数存在显著相关 (r12 .3 4 =0 2 3 0 2 ) ,被片数与雄蕊数存在极显著相关 (r14 .2 3 =0 .472 7 )以及花柱数与胚珠数之间存在极显著相关(r2 3 .14 =0 .7787 ) ,这暗示被片、花柱、胚珠、雄蕊在遗传或发育上是相关的     

Unique growth paths of heterospecific pollen tubes result in late entry into ovules in the gynoecium of Sagittaria (Alismataceae)

• Pollen‐pistil interactions are a fundamental process in the reproductive biology of angiosperms and play a particularly important role in maintaining incipient species that exist in sympatry. However, the majority of previous studies have focused on species with syncarpous gynoecia (fused carpels) and not those with apocarpous gynoecia (unfused carpels).
• In the present study, we investigated the growth of conspecific pollen tubes compared to heterospecific pollen tubes in Sagittaria species, which have apocarpous gynoecia. We conducted controlled pollinations between S. pygmaea and S. trifolia and observed the growth of conspecific and heterospecific pollen tubes under a fluorescence microscope.
• Heterospecific and conspecific pollen tubes arrived at locules within the ovaries near simultaneously. However, conspecific pollen tubes entered into the ovules directly, whereas heterospecific tubes passed through the carpel base and adjacent receptacle tissue, to ultimately fertilize other unfertilized ovules. This longer route taken by heterospecific pollen tubes therefore caused a delay in the time required to enter into the ovules. Furthermore, heterospecific pollen tubes displayed similar growth patterns at early and peak pollination. The growth pattern of heterospecific pollen tubes at late pollination was similar to that of conspecific pollen tubes at peak pollination.
• Heterospecific and conspecific pollen tubes took different routes to fertilize ovules. A delayed entry of heterospecific pollen into ovules may be a novel mechanism of conspecific pollen advantage (CPA) for apocarpous species.

     

大花萱草‘金娃娃’雌雄蕊发育进程及其与花蕾长度的相关性研究

采用石蜡切片法对大花萱草'金娃娃'(Hemerocallis hybridus cv.'Stella de oro')不同花蕾长度时雌雄蕊的形态及其发育时期进行观察,以探讨花营长度与雌雄蕊发育进程的相关性.结果显示:(1)'金娃娃'雄蕊发育正常,小孢子发生及雄配子体的发育过程与常见单子叶植物类似,成熟花粉属二胞型;雌蕊子房具多胚珠,但各胚珠中雌配子体发育进程不同步,出现大量无胚囊或胚囊内核发育紊乱、解体的现象而导致雌配子体发育不正常,大田结实率不到5%且种子干瘪不能发芽.(2)'金娃娃'花蕾长度与花粉发育时期具有相关性,为花蕾长度作为组织培养外植体取材外形标准提供丁植物胚胎学依据.     

Molecular cloning and characterization of cDNA encoding cardosin B,an aspartic proteinase accumulating extracellularly in the transmitting tissue of Cynara cardunculus L.

Cardosins A and B are related aspartic proteinases from the pistils of Cynara cardunculus L., whose milk-clotting activity has been exploited for the manufacture of cheese. Here we report the cloning of cardosin B cDNA and its organ, tissue and cytological localization. The cDNA-derived amino acid sequence has 73% similarity with that of cardosin A and displays several distinguishing features. Cardosin B mRNA was detected in young inflorescences but not in pistils of fully opened inflorescences, indicating that its expression is developmentally regulated. The proteinase, however, accumulates in the pistil until the later stages of floral development. Immunocytochemistry with a monospecific antibody localized cardosin B to the cell wall and extracellular matrix of the floral transmitting tissue. The location of cardosin B in the pistil is therefore clearly different from that of cardosin A, which was found at protein storage vacuoles of the stigmatic papillae and has been suggested to be involved in RGD-mediated proteolytic mechanisms. In view of these results the possible functions of cardosin B in the transmitting tissue are discussed.     

Pollination-induced ethylene promotes the early phase of pollen tube growth in Petunia inflata

In Petunia inflata, a species with gametophytic self-incompatibility, pollination triggers two phases of ethylene production by the pistil, the first of which peaks 3 hours after pollination with compatible or incompatible pollen. To investigate the physiological significance of the first phase of ethylene production, pollinated flowers were treated with 2,5-norbornadiene (NBD), an inhibitor of ethylene action. Treatment with NBD reduced pollen tube growth in a dose-dependent manner during the first six hours after pollination; however, pollen tube growth was insensitive to NBD if the treatment was applied 6 hours or more after pollination. Simultaneous application of exogenous ethylene substantially offset the inhibitory effects of NBD in flowers pollinated for 4 hours. Another inhibitor of ethylene action, 1-methylcyclopropene (1-MCP), also produced a strong inhibition of pollen tube growth during the first six hours of pollination. The experiments with 1-MCP pretreatment indicate that pistil tissues are the primary target of the pollination-induced ethylene.