转基因技术生产无籽果实的新策略

无籽果实具有许多优点,深受人们喜爱。传统无籽果实生产方法存在着诸如单性结实品种少、外用激素施用量不易掌握及四倍体品种较难获得等一系列问题。分子遗传研究表明,植物基因组中含有影响单性结实的基因,某些来自于细菌的基因也可在植物激素生物合成途径中起调节作用。应用这些目的基因,已建立了转基因生产无籽果实的新策略,如在种皮或子房特异性启动子控制下的生长素基因或细胞毒素基因的表达及“终止子”技术的运用等,这将大规模地促进蔬菜和水果生产,提高果蔬产品的市场价值。     

浅析单性结实

植物子房不经受精作用而发育成果实的现象叫做单性结实,由单性结实形成的果实称为无籽果实。无籽果实中不含种子或含无胚的种子。在自然界中,单性结实有两种类型,即营养性单性结实和刺激性单性结实。前者在形成无籽果实时是不经任何刺激就能实现的,如香蕉,风梨、菠萝等;而后者在形成无籽果实时是需经花粉或激素刺激才能实现的,如无籽西瓜、无籽番茄、无籽葡萄等。     

单性结实与无籽番茄、无籽西瓜的培育

被子植物传粉受精后 ,胚珠开始发育并产生大量生长素使子房增大发育成果实。但自然界中也有些植物在开花后不通过受精作用子房发育成果实 ,但无种子。因此在发育成熟的果实里 ,有的含种子 ,有的不含种子 ;前者称为有籽果实 ,后者称为无籽果实 ,生物学上也把后者的结实方式称为单性结实。单性结实有天然的单性结实 (或称自动的单性结实 )和刺激性单性结实 (或称被动的单性结实 )。天然的单性结实是指不需要经过传粉刺激和其他刺激 ,子房就发育为无籽果实的 ,如香蕉、凤梨、无籽柑橘、无籽柠檬 ,在番茄、黄瓜和胡椒等植物中也偶有发生。这种类…     

植物激素对果树单性结实调控的研究进展

尽管种子与果实的发育过程密切相关,但由于无籽果实提高了果实的品质并延长了货架期,因此无籽果实受到生产者和消费者的广泛青睐。果实的生长受激素调控,而相关研究也初步揭示了激素在单性结实果实形成过程中的作用。本文对单性结实的概念、诱导单性结实的激素种类及功能、诱导机理,以及转基因技术在单性结实果实生产中的应用概况进行了综述,以期为果树单性结实的研究提供参考。     

无籽枇杷研究初报

利用冻害果实、生长调节剂诱导、多倍体品种等进行无籽枇杷生产试验,结果表明,生长调节剂诱导及利用多倍体品种是生产无籽枇杷果实的较佳方法。     

5个生物学易混概念辨析

1 单性生殖与单性结实 单性生殖是由有性生殖细胞（未受精的卵细胞或精子）直接发育而成,属有性生殖中的单性生殖。单性结实是由于雌蕊不能产生正常的生殖细胞或没有受粉使子房发育为无籽果实叫单性结实。     

枇杷胚乳愈伤组织的诱导和异常器官的分化

枇杷(Eriobotrya japonica Lindl.)是我国特产的优良亚热带水果。但是,与一般的水果比较,枇杷的种子较多,较大,因而可食用果肉部分的比例较少,所以培育无籽枇杷的研究很有诱人的前景。枇杷果实中种子总重量与果重成正相关,用赤霉素处理能引起单性结实,产生无籽果实。但单性结实的果实通常比有籽的果实小[8]。     

用单性结实基因2A11-iaaM转化罗汉果的研究

为了实现罗汉果生产中免除人工授粉和果实无籽化,该研究利用pBI121-Gus构建果实特异启动子2A11与生长素合成相关基因iaaM的嵌合基因(2A11-iaaM)过量表达载体,以罗汉果雌株叶盘为材料,采用农杆菌介导法建立罗汉果高效遗传转化体系,转化和创制单性结实罗汉果种质,通过基因特异引物对的PCR扩增,初步检测出转基因阳性植株,将之移栽大田,观察转基因植株的单性结实性的表现。结果表明:构建罗汉果单性结实性相关的pBAI-Gus植物双元表达载体获得成功;建立了农杆菌介导的罗汉果叶盘遗传转化优化体系,即农杆菌菌液OD_(600)值为0.3～0.5,侵染10 min,最优选择培养基为MS+TDZ 0.7 mg·L~(-1)+IBA 0.5 mg·L~(-1)+Kan 5 mg·L~(-1)+Cef 300 mg·L~(-1);经PCR鉴定共获得4株转基因阳性雌株;将阳性植株扩繁后移栽田间,经田间调查发现,24株阳性扩繁植株中有5株正常开花,占总植株数的20.8%,且其子房未经人工授粉发育成幼果,表现单性结实性。在载体构建和农杆菌介导的罗汉果遗传转化体系优化的基础上,将外源单性结实相关嵌合基因整合进罗汉果基因组并得到表达,为后续研究单性结实罗汉果的遗传生理,创制转基因罗汉果单性结实新种质,以及克服其产业化中需要人工授粉和无籽化提供了理论和应用基础。     

植物的单性结实

在高中生物必修本第122页上讲到:利用人工合成的一定浓度的生长素溶液处理没有受粉的番茄花蕾,就能获得无籽番茄。这实际上就是番茄的单性结实。 什么叫单性结实呢?凡是不经受精作用而形成不含种子的果实,叫单性结实。单性结实有天然性单性结实和刺激性单性结实之分。天然性单性     

自然界中的无籽果实是怎样形成的?

绿色开花植物的个体发育是从受精卵开始的,它在生殖上具有独特的双受精现象。卵细胞受精后发育形成胚(幼小植物的雏体),受精极核发育成胚乳,整个胚珠发育成种子,子房发育成为果实。但自然界中也有些植物在开花后不经过受精作用也能结出果实,但无种子。因此在发育成熟的果实里,有的含种子,有的不含种子;前者称为有籽果实,后者称为无籽果实,生物学上也把后者称为单性结实。在被子植物中,能够结出无籽果实有三种情况:一是不经过授粉和其他刺激而产生果实的,如香蕉、凤梨、无子柑桔、无籽柠檬,在番茄、南瓜、黄瓜、胡椒等植物中也偶有发生;这种…     

Induction of parthenocarpy in tomato via specific expression of the<Emphasis Type="Italic"> rolB</Emphasis> gene in the ovary

The molecular signals for the development of the ovary into fruit following ovule fertilization are not clear. However, in many species, including tomato ( Lycopersicon esculentum Mill.), auxins and auxin transport inhibitors can substitute for fertilization as activators of fruit set, suggesting that this plant hormone plays a key role in this process. In agreement, transgenes for auxin biosynthesis expressed under ovary- or ovule-specific promoters were shown earlier to enable parthenocarpic (i.e. seedless) fruit development. In the present study, we tested an alternative approach for the induction of parthenocarpy that is based on ovary-specific expression of the Agrobacterium rhizogenes-derived gene rolB. This gene was chosen because rolB transgenic plants manifest several syndromes characteristic of auxin treatment. Tomato plants transformed with a chimeric construct containing the rolB gene fused to the ovary- and young-fruit-specific promoter TPRP-F1 developed parthenocarpic fruits. Fruit size and morphology, including jelly fill in the locules of the seedless fruits, were comparable to those of seeded fruits of the parental line. Although it is not known whether ROLB signals for the same cassette of genes involved in fertilization-dependent fruit development, it clearly activates a battery of genes that enable successful completion of seedless fruit development in tomato.     

Parthenocarpic fruit development in tomato

Abstract: Parthenocarpic fruit development is a very attractive trait for growers and consumers. In tomato, three main sources of facultative parthenocarpy, pat, pat-2, pat-3/pat-4, are known to have potential applications in agriculture. The parthenocarpic fruit development in these lines is triggered by a deregulation of the hormonal balance in some specific tissues. Auxins and gibberellins are considered as the key elements in parthenocarpic fruit development of those lines. An increased level of these hormones in the ovary can substitute for pollination and trigger fruit development. This has opened up genetic engineering approaches for parthenocarpy that have given promising results, both in quality and quantity of seedless fruit production.     

Cloning of an ovule specific promoter from Arabidopsis thaliana and expression of beta-glucuronidase

Tissue specific expression of transgenes in plant species has several advantages over constitutive expression. Identification of ovule specific promoters would be useful in genetic engineering of plants with a variety of desirable traits such as genetically engineered parthenocarpy, female sterile plants or seedless fruits. Relative inaccessibility and difficulty in harvesting adequate amounts of tissue at known developmental stages has impeded the progress in cloning of promoters involved in ovule development. In the present study an ovule specific promoter was cloned from Arabidopsis AGL11 gene and used to express GUS (beta-glucuronidase) gene in transgenic Arabidopsis. Histochemical staining of GUS appeared in the center of young ovary (ovules), but no detectable GUS activity was observed in vegetative plant tissues, sepals, petals and androecium. AGL11 gene promoter can be useful to modify the developmental path of plants by expressing either plant hormones or lethal genes for agronomic purpose.     

Tomato facultative parthenocarpy results from SlAGAMOUS‐LIKE 6 loss of function

The extreme sensitivity of the microsporogenesis process to moderately high or low temperatures is a major hindrance for tomato (Solanum lycopersicum) sexual reproduction and hence year‐round cropping. Consequently, breeding for parthenocarpy, namely, fertilization‐independent fruit set, is considered a valuable goal especially for maintaining sustainable agriculture in the face of global warming. A mutant capable of setting high‐quality seedless (parthenocarpic) fruit was found following a screen of EMS‐mutagenized tomato population for yielding under heat stress. Next‐generation sequencing followed by marker‐assisted mapping and CRISPR/Cas9 gene knockout confirmed that a mutation in SlAGAMOUS‐LIKE 6 (SlAGL6) was responsible for the parthenocarpic phenotype. The mutant is capable of fruit production under heat stress conditions that severely hamper fertilization‐dependent fruit set. Different from other tomato recessive monogenic mutants for parthenocarpy, Slagl6 mutations impose no homeotic changes, the seedless fruits are of normal weight and shape, pollen viability is unaffected, and sexual reproduction capacity is maintained, thus making Slagl6 an attractive gene for facultative parthenocarpy. The characteristics of the analysed mutant combined with the gene's mode of expression imply SlAGL6 as a key regulator of the transition between the state of ‘ovary arrest’ imposed towards anthesis and the fertilization‐triggered fruit set.     

Early anther ablation triggers parthenocarpic fruit development in tomato

Fruit set and fruit development in tomato is largely affected by changes in environmental conditions, therefore autonomous fruit set independent of fertilization is a highly desirable trait in tomato. Here, we report the production and characterization of male‐sterile transgenic plants that produce parthenocarpic fruits in two tomato cultivars (Micro‐Tom and Moneymaker). We generated male‐sterility using the cytotoxic gene barnase targeted to the anthers with the PsEND1 anther‐specific promoter. The ovaries of these plants grew in the absence of fertilization producing seedless, parthenocarpic fruits. Early anther ablation is essential to trigger the developing of the transgenic ovaries into fruits, in the absence of the signals usually generated during pollination and fertilization. Ovaries are fully functional and can be manually pollinated to obtain seeds. The transgenic plants obtained in the commercial cultivar Moneymaker show that the parthenocarpic development of the fruit does not have negative consequences in fruit quality. Throughout metabolomic analyses of the tomato fruits, we have identified two elite lines which showed increased levels of several health promoting metabolites and volatile compounds. Thus, early anther ablation can be considered a useful tool to promote fruit set and to obtain seedless and good quality fruits in tomato plants. These plants are also useful parental lines to be used in hybrid breeding approaches.     

Pollen Morphology and Boron Concentration in Floral Tissues as Factors Triggering Natural and GA-Induced Parthenocarpic Fruit Development in Grapevine

Parthenocarpic fruit development (PFD) reduces fruit yield and quality in grapevine. Parthenocarpic seedless berries arise from fruit set without effective fertilization due to defective pollen germination. PFD has been associated to micronutrient deficiency but the relation of this phenomenon with pollen polymorphism has not been reported before. In this work, six grapevine cultivars with different tendency for PFD and grown under micronutrient-sufficient conditions were analyzed to determine pollen structure and germination capability as well as PFD rates. Wide variation in non-germinative abnormal pollen was detected either among cultivars as well as for the same cultivar in different growing seasons. A straight correlation with PFD rates was found (R² = 0.9896), suggesting that natural parthenocarpy is related to defective pollen development. Such relation was not observed when PFD was analyzed in grapevine plants exposed to exogenous gibberellin (GA) or abscissic acid (ABA) applications at pre-anthesis. Increase (GA treatment) or reduction (ABA treatment) in PFD rates without significative changes in abnormal pollen was determined. Although these plants were maintained at sufficient boron (B) condition, a down-regulation of the floral genes VvBOR3 and VvBOR4 together with a reduction of floral B content in GA-treated plants was established. These results suggest that impairment in B mobility to reproductive tissues and restriction of pollen tube growth could be involved in the GA-induced parthenocarpy.