Identification of self-incompatibility (S-) locus linked pollen cDNA markers in Petunia inflata.

Solanaceous type self-incompatibility (SI) is controlled by a single polymorphic locus, termed the S-locus. The only gene at the S-locus that has been characterized thus far is the S-RNase gene, which controls pistil function, but not pollen function, in SI interactions between pistil and pollen. One approach to identifying additional genes (including the pollen S-gene, which controls pollen function in SI) at the S-locus and to study the structural organization of the S-locus is chromosome walking from the S-RNase gene. However, the presence of highly repetitive sequences in its flanking regions has made this approach difficult so far. Here, we used RNA differential display to identify pollen cDNAs of Petunia inflata, a self-incompatible solanaceous species, which exhibited restriction fragment length polymorphism (RFLP) for at least one of the three S-haplotypes (S1, S2, and S3) examined. We found that the genes corresponding to 10 groups of pollen cDNAs are genetically tightly linked to the S-RNase gene. These cDNA markers will expedite the mapping and cloning of the chromosomal region of the Solanaceae S-locus by providing multiple starting points.     

New views of S-RNase-based self-incompatibility

S-RNase-based self-incompatibility (SI) is the most widespread form of genetically controlled mate selection in plants. S-RNase controls pollination specificity in the pistil, while the newly discovered SLF/SFB controls pollination specificity in the pollen. A widely discussed model suggests that compatibility is explained by ubiquitylation and degradation of nonself-S-RNase and that, conversely, incompatibility is caused by failure to degrade self-S-RNase. This model is consistent with the long-standing view that S-RNase inhibition is central to SI. Recent results show, however, that S-RNase is compartmentalized in pollen tubes and, significantly, that compatibility might not require SLF/SFB. S-RNase compartmentalization and dislocation into the pollen tube cytoplasm might be similar to the trafficking of other cytotoxins such as ricin.     

Influences of Cross Pollination on Pollen Tube Growth and Fruit Set in Zuili Plums （Prunus salicina）

Zuili plum （Prunus salicina L.） trees usually set fruit poorly, although they produce high quality fruit. To elucidate the causes of the poor fruit set, pollen tube growth into pistils and fruit set percentage were investigated after cross-, self- and open-pollination. Ovule development in Zuili pistils was also investigated. Pollen tube penetration into the ovules via the obturator and micropyle was best when Zuili pistils were pollinated by cv. Black Amber （P. domestica） pollen grains, although cross-pollinations with Hongxinli and Miili （P. salicina） pollen were more effective than self- and open-pollination. The fruit set percentage was also highest in pistils pollinated with Black Amber pollen grains. Morphological observation of Zuili pistils revealed that the trees produce ＂double pistils＂, developing two ovaries from a basal pistil, at a rate as high as 28%. In such abnormal pistils, most ovules were lacking an embryo sac or were entirely degenerated. The percentage of normally developed ovules was 24.3% and 8.9% in normal and double pistils, respectively. From these results, we conclude that the main causes of poor fruit set of Zuili plums are a lack of effective cross-pollination and the production of high percentages of double pistils in which normally developed ovules are scarcely formed.     

Pollination in vitro: effects on the growth of pollen tubes,seed set and gametophytic self-incompatibility in Trifolium pratense L. and T. repens L.

Summary Growth of pollen tubes and seed set were compared after hand pollination in situ and in vitro in two self-incompatible species, Trifolium pratense and Trifolium repens. Adhesion of pollen grains to the stigma was greater in vitro for both species. After cross-pollination, in vitro culture gave a significant increase in the cumulative growth of pollen tubes in pistils of T. pratense compared to in situ conditions. After selfing in T. repens, pollen tube growth was significantly increased by in vitro culture of florets. Seed set after crossing in situ and in vitro was similar for both species. Seed set after selfing in vitro was not increased in T. pratense. Several genotypes of T. repens were classified as very good, good and poor selfers based on their capacity for seed set following selfing in situ. In vitro pollination increased self seed formation by 1.7-, 18.0- and 31.0-fold for each class, respectively. Ovules located nearest to the style were fertilized more often after selfing than after crossing.     

Progamic phase and fertilization inGasteria verrucosa (Mill.) H. Duval: pollination signals

A summary is given of the pollen tube pathway, the interactions during the progamic phase and the incompatibility system ofGasteria. Pollen coating substances stimulate pollen tube ovular penetration and fruit set in cases of cross-pollination. Pollen coating substances also stimulate the water supply of the pistil which completes the pollen tube pathway. These two types of signals are related to recognition reactions, as well as to the activation of the pistil. Because the pollen coating substance is of sporophytic origin, the incompatibility system type is discussed.     

Rapid floral senescence following male function and breeding systems of some tropical orchids

No comparative study of floral senescence following male function among a range of tropical orchid genera has previously been undertaken. The timing and pattern of floral senescence and occurrence of fruit formation were studied following self-, geitonogamous and cross-pollination in 14 epiphytic and two terrestrial orchid species to determine their breeding system and assess the occurrence of floral abscission following pollinaria removal. Both pollination and pollinaria removal caused rapid floral senescence, and the pattern and timing of the floral changes were the same in all treatments. Six Dendrobium species and Pelatantheria insectifera were self-incompatible (SI) and eight other species, including one terrestrial species, were self-compatible (SC). Capsules produced from outcrossing in four SC species, Phalaenopsis cornu-cervi, Eria pubescens, Cleisostoma appendiculatum and Arundina graminifolia, were larger and heavier than those produced after selfing. Reductions in flower life span following pollinaria removal were positively correlated with flower size and longevity of unpollinated flowers but not with position in the inflorescence or nature of the breeding system. Rapid flower senescence following pollinaria removal reported here suggests that it may be widespread in tropical species. The significant association of the response with size of flowers and inflorescences among the species studied suggests that the cost of flower maintenance outweighs the benefit of remaining open for female function after pollinaria have been removed. Both SC and SI species were found among tropical orchids, but variation in capsule size following self- and cross-pollination indicates that there may be a reduction in seed production following selfing, even in SC species, and that fruit formation alone should not be taken as reliable evidence of full self-compatibility.     

Self-incompatibility and interspecific incompatibility: relationships in intra- and interspecific crosses of Zinnia elegans Jacq. and Z. angustifolia HBK (Compositae)

Summary Intraspecific and reciprocal interspecific crosses involving Zinnia angustifolia clones and Z. elegans lines showed that in both species, sporophytic self-incompatibility (SI) systems were present. Intensity of SI varied among clones and lines, and high self seed set was associated with a concomitant decrease in callose fluorescence in papillae and pollen tubes. Incomplete stigmatic inhibition of pollen germination and tube growth was observed in reciprocal interspecific crosses and associated with callose synthesis, suggesting S-gene activity. Seed set and progeny obtained following Z. angustifolia×Z. elegans matings was comparable to intraspecific compatible matings of Z. angustifolia although the rate of pollen tube growth through the style was slower. In Z. elegans × Z. angustifolia matings, additional prezygotic barriers were present and acted between pollen tube penetration of the stigma and syngamy. SI X SI interspecific incompatibility was essentially unilateral, with no embryos or progeny obtained when Z. elegans was the pistillate parent. It was hypothesized that nonfunctioning of Z. elegans × Z. angustifolia crosses was due to S-gene expression at the stigmatic surface and to other isolating mechanisms in the stylar or ovarian transmitting tissue.Scientific Article No. A-4448, Contribution No. 7439 of the Maryland Agricultural Experiment Station, Department of HorticultureA portion of this paper was presented in the report: Boyle TH, Stimart DP (1986) Incompatibility relationships in intra- and interspecific crosses of Z. elegans Jacq. and Z. angustifolia HBK (Compositae). In: Mulcahy D (ed) Biotechnology and ecology of pollen. Springer, New York     

Differential ovule development following self- and cross-pollination: the basis of self-sterility in Narcissus triandrus (Amaryllidaceae)

Self-pollination results in significantly lower seed set than cross-pollination in tristylous Narcissus triandrus. We investigated structural and functional aspects of pollen–pistil interactions and ovule–seed development following cross- and self-pollination to assess the timing and mechanism of self-sterility. Ovule development within an ovary was asynchronous at anthesis. There were no significant differences in pollen tube behavior following cross- vs. self-pollination during the first 6 d of growth, regardless of style morph type. Double fertilization was significantly higher following cross- vs. self-pollination. Aborted embryo development was not detected following either pollination type up to seed maturity. Prior to pollen tube entry, a significantly greater number of ovules ceased to develop following self- vs. cross-pollination. These results indicate that self-sterility in N. triandrus operates prezygotically but does not involve differential pollen tube growth typical of many self-incompatibility (SI) systems. Instead, low seed set following self-pollination is caused by a reduction in ovule availability resulting from embryo sac degeneration. We hypothesize that this is due to the absence of a required stimulus for normal ovule development. If this is correct, current concepts of SI may need to be broadened to include a wider range of pollen–pistil interactions.     

On the origin of self-incompatibility haplotypes: transition through self-compatible intermediates

Self-incompatibility (SI) in flowering plants entails the inhibition of fertilization by pollen that express specificities in common with the pistil. In species of the Solanaceae, Rosaceae, and Scrophulariaceae, the inhibiting factor is an extracellular ribonuclease (S-RNase) secreted by stylar tissue. A distinct but as yet unknown gene (provisionally called pollen-S) appears to determine the specific S-RNase from which a pollen tube accepts inhibition. The S-RNase gene and pollen-S segregate with the classically defined S-locus. The origin of a new specificity appears to require, at minimum, mutations in both genes. We explore the conditions under which new specificities may arise from an intermediate state of loss of self-recognition. Our evolutionary analysis of mutations that affect either pistil or pollen specificity indicates that natural selection favors mutations in pollen-S that reduce the set of pistils from which the pollen accepts inhibition and disfavors mutations in the S-RNase gene that cause the nonreciprocal acceptance of pollen specificities. We describe the range of parameters (rate of receipt of self-pollen and relative viability of inbred offspring) that permits the generation of a succession of new specificities. This evolutionary pathway begins with the partial breakdown of SI upon the appearance of a mutation in pollen-S that frees pollen from inhibition by any S-RNase presently in the population and ends with the restoration of SI by a mutation in the S-RNase gene that enables pistils to reject the new pollen type.     

Self-incompatibility in passion fruit: cellular responses in incompatible pollinations

Self-incompatibility (SI) is a genetic mechanism in angiosperms that prevents selfing. The SI system in passion fruit (Passiflora edulis Sims) was investigated using hand pollinations. Pollen tube growth was inspected by microscopy, and sequence analysis of potential regulators of this process was carried out. The results revealed that the pollen tubes grew slowly and were often completely arrested in the stigma in an incompatible combination. Under these circumstances the pollen tube was rapidly and significantly rearranged, followed by the rapid deposition of callose in the stigma during the SI response. The structural changes in the pollen grain after an incompatible pollination were investigated using scanning electron microscopy. Furthermore, ultrastructural observations during incompatible interactions showed that the membrane system of the pollen tube was damaged, and fertilisation was not observed or was considerably delayed when compared to compatible interactions. The analysis presented here provides evidence that the passion fruit genome presents similar sequences to those encoding factors involved in SI in different species. These results suggest that, in the SI system of passion fruit, the rejection of an incompatible pollen grain is characterised by drastic structural changes in both pollen and pollen tube.     

Pollination biology of the saprophytic speciesPetrosavia sakuraii (Makino) van Steenis in Central Japan

Pollination biology of the saprophytic speciesPetrosavia sakuraii was investigated in Central Japan. The flower opens at any time of the day, and the anthers of outer stamens dehisce after about one day and those of the inner stamens after two days. The stigmata on the semicarpous (nearly apocarpous) pistil, which are already receptive when the flower opens, are situated in the center of the flower and move gradually outwards to touch the anthers of outer stamens about five days after anthesis. The breeding experiments show that the stigmata are receptive at least for five days, and many seeds are produced through autonomous self-pollination. That means the nearly apocarpous pistil, which is in a primitive condition, is adapted to the autonomous self-pollination. The selfing rate including insect-mediated self-pollination is very high, and this sexual-reproductive system seems favorable to the saprophytic plant which is probably severely limited in its resources. However, cross-pollination also may be performed by the small bees of Lasioglossum and some other insects, even though they do not so frequently visit the flowers and the out-crossing rate is low.     

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.     

Reproductive strategies of diploid and polyploid populations of arcticDraba (Brassicaceae)

132 cultivated populations (2x–16x) of 15 arctic-alpine species ofDraba were investigated to clarify a possible relationship between reproductive strategies and polyploid evolution in the genus. The populations were exclusively sexual and produced viable seed after spontaneous self-pollination, but showed large variation both in traits promoting cross-pollination and in autogamous fruit and seed set. Traits promoting cross-pollination, e.g., floral display, protogyny, and delayed selfing, were positively correlated, and these traits were negatively correlated with autogamous fruit and seed set. All diploid and many polyploid populations had high autogamous seed set and small, unscented, non-protogynous, and rapidly selfing flowers. In contrast, all populations with low autogamous seed set and large, scented, and strongly protogynous flowers with distinctly delayed selfing were polyploid. These results are consistent with those previously obtained from enzyme electrophoresis, suggesting that the genetically depauperate diploids are extreme inbreeders and that the highly fixed-heterozygous polyploids vary from extreme inbreeders to mixed maters. The reproductive data lend additional support to the hypothesis that allopolyploidy in arcticDraba serves as an escape from genetic depauperation caused by uniparental inbreeding at the diploid level.     

Self pollination and resource availability affect ovule abortion inCassia fasciculata (Caesalpiniaceae)

We examined the effects of pollen source and resource availability on ovule abortion in the annual legumeCassia fasciculata. Pollen source was controlled by hand-pollinating flowers with cross- or self-pollen. Resource availability to developing fruits was controlled by adjusting fruit loads (heavy versus light) on each plant and exposing plants to different photoperiod cycles (16 vs 12 h of light; short days favor fruit growth at the expense of vegetative growth). In mature fruits the proportion of ovules expanding (showing some development over virgin ovules) ranged from 89–95% and did not increase with resource availability, suggesting that unexpanded ovules were either unfertilized or obligately aborted shortly after fertilization. The proportion of expanded ovules maturing in mature fruits was near 97% for both self- and crosspollinations in the treatment with highest resource availability (light load, short days) and lower in the remaining treatments, where self-pollination resulted in up to 9% lower seed maturation than cross-pollination. In the latter three treatments a pollen source effect was dependent upon the maternal plant; in some plants selfing increased abortion and in others it did not. Collectively, the results suggest that (1) both pollen source and resource availability affect ovule abortion, (2) at least some abortion is facultative, and (3) when resources are limited, self-pollination increases abortion in some but not all maternal plants.     

The S locus of flowering plants: when self-rejection is self-interest.

In certain families of flowering plants, a self-incompatibility (SI) locus prevents self-fertilization, by a specific interaction between the S-gene product produced in the pistil and the S-gene products borne on or expressed by the male gametophyte, the pollen grain. The female S-locus gene products for two families showing different types of SI have been putatively identified as major pistil glycoproteins (the S-locus-specific glycoproteins of the Brassicaceae and the S-RNases of the Solanaceae). However, they are distinct in sequence and mode of action. The nature of the S-locus gene product borne by the pollen is still uncertain in both systems.     

Effects of genotype and temperature on pollen tube growth in perennial ryegrass (Lolium perenne L.)

Summary Low yield in seed crops of perennial ryegrass is related to low fertilization efficiency and low temperature during anthesis. To study the effect of genotype and temperature on pollen performance, we conducted greenhouse experiments at controlled temperatures. Individual florets of four genotypes that are known to differ in seed production were hand pollinated at four temperatures (14°, 18°, 22°, 26° C) both in vivo and via a semiin-vitro method involving excised florets on agar. Pollen germination and tube growth were determined with UV-fluorescence microscopy and scored in six classes at 2 h after pollination in vitro and after 0.5, 2 and 5 h in vivo. In vitro, both genotype and temperature had a significant effect on the performance of self-pollen. Pollen tube growth increased with temperature. In cross-pollinations, the pistil parent had a significant effect on pollen tube growth, and there was also a significant pistil-by-temperature interaction. In vivo, genotype and temperature significantly affected pollen performance. The genotype-by-temperature interaction was only significant 5 h after pollination. One genotype with low seed yield was pseudoself-compatible and was a relatively poor mother after cross-pollination. The effects of genotype and temperature on the growth of self-pollen might be exploited in a breeding programme.A.G. Stephenson was on a sabbattical leave at SVP in 1987     

核果类果树自交不亲和性研究进展

综述了核果类果树甜樱桃(PFunus avium L.)、杏(P.armeniaca L.)、扁桃(P.dulcis(Mill.)D.A.Webb)和梅(P.mume Sieb)等自交不亲和性的研究进展.着重讨论了S-RNase基因(s基因)和SLF基因(S-locus F-box基因,或称SFB基因),S基因在杂交后代群体中的遗传规律,利用S基因的遗传特性选育自交亲和品种和确定S基因型的主要方法及其特点以及自交亲和机制的几种可能的类型.     

Transgenic American elm shows reduced Dutch elm disease symptoms and normal mycorrhizal colonization

The American elm (Ulmus americana L.) was once one of the most common urban trees in eastern North America until Dutch-elm disease (DED), caused by the fungus Ophiostoma novo-ulmi, eliminated most of the mature trees. To enhance DED resistance, Agrobacterium was used to transform American elm with a transgene encoding the synthetic antimicrobial peptide ESF39A, driven by a vascular promoter from American chestnut. Four unique, single-copy transgenic lines were produced and regenerated into whole plants. These lines showed less wilting and significantly less sapwood staining than non-transformed controls after O. novo-ulmi inoculation. Preliminary observations indicated that mycorrhizal colonization was not significantly different between transgenic and wild-type trees. Although the trees tested were too young to ensure stable resistance was achieved, these results indicate that transgenes encoding antimicrobial peptides reduce DED symptoms and therefore hold promise for enhancing pathogen resistance in American elm.