Pollination- or Wound-Induced Kaempferol Accumulation in Petunia Stigmas Enhances Seed Production

Genome-Wide Identification of the WD40 Gene Family in Walnut (Juglans regia L.) and Its Expression Profile in Different Colored Varieties

The walnut (Juglans regia) is a woody oilseed crop with high economic and food value as its kernels are edible and its hulls can be widely used in oil extraction and plugging, chemical raw materials, and water purification. Currently, red walnut varieties have emerged, attracting consumer interest due to their high nutritional values as they are rich in anthocyanins. WD40 is a widespread superfamily in eukaryotes that play roles in plant color regulation and resistance to stresses. In order to screen for JrWD40 associated with walnut color, we identified 265 JrWD40s in walnuts by genome-wide identification, which were unevenly distributed on 16 chromosomes. According to the phylogenetic tree, all JrWD40s were classified into six clades. WGD (Whole genome duplication) is the main reason for the expansion of the JrWD40 gene family. JrWD40s were relatively conserved during evolution, but their gene structures were highly varied; lower sequence similarity may be the main reason for the functional diversity of JrWD40s. Some JrWD40s were highly expressed only in red or green walnuts. In addition, we screened 16 unique JrWD40s to walnuts based on collinearity analysis. By qRT-PCR, we found that JrWD40-133, JrWD40-150, JrWD40-155, and JrWD40-206 may regulate anthocyanin synthesis through positive regulation, whereas JrWD40-65, JrWD40-172, JrWD40-191, JrWD40-224, and JrWD40-254 may inhibit anthocyanin synthesis, suggesting that these JrWD40s are key genes affecting walnut color variation.

Ultrasonic-Assisted Extraction of Phenolic Compounds from Lonicera similis Flowers at Three Harvest Periods: Comparison of Composition, Characterization, and Antioxidant Activity

Lonicera similis Hemsl. (L. similis) is a promising industrial crop with flowers rich in phenolic compounds. In this study, an ultrasound-assisted extraction (UAE) was designed to extract phenolic compounds from L. similis flowers (LSFs). A contrastive analysis on the phenolic compounds' yield and characterization and the antioxidant activity of the extracts at three harvest stages (PGS I, PGS II, and PGS III) are reported. The results indicate that the optimal conditions are a sonication intensity of 205.9 W, ethanol concentration of 46.4%, SLR of 1 g: 31.7 mL, and sonication time of 20.1 min. Under these optimized conditions, the TPC values at PGS I, PGS II, and PGS III were 117.22 ± 0.55, 112.73 ± 1.68, and 107.33 ± 1.39 mg GAE/g, respectively, whereas the extract of PGS I had the highest TFC (68.48 ± 2.01 mg RE/g). The HPLC analysis showed that chlorogenic acid, rutin, quercetin, isoquercitrin, and ferulic acid are the main components in the phenolic compounds from LSFs, and their contents are closely corrected with the harvest periods. LSF extracts exhibited a better antioxidant activity, and the activity at PGS I was significantly higher than those at PGS II and PGS III. The correlation analysis showed that kaempferol and ferulic acid, among the eight phenolic compounds, have a significant positive correlation with the antioxidant activity, while the remaining compounds have a negative correlation. Minor differences in extracts at the three harvest stages were found through SEM and FTIR. These findings may provide useful references for the optimal extraction method of phenolic compounds from LSFs at three different harvest periods, which will help to achieve a higher phytochemical yield at the optimal harvest stage (PGS I).

VvWRKY5 positively regulates wounding-induced anthocyanin accumulation in grape by interplaying with VvMYBA1 and promoting jasmonic acid biosynthesis

Wounding stress induces the biosynthesis of various secondary metabolites in plants, including anthocyanin. However, the underlying molecular mechanism remains elusive. Here, we reported that a transcription factor, VvWRKY5, promotes wounding-induced anthocyanin accumulation in grape (Vitis vinifera). Biochemical and molecular analyses demonstrated that wounding stress significantly increased anthocyanin content, and VvMYBA1 plays an essential role in this process. VvWRKY5 could interact with VvMYBA1 and amplify the activation effect of VvMYBA1 on its target gene VvUFGT. The transcript level of VvWRKY5 was notably induced by wounding treatment. Moreover, our data demonstrated that VvWRKY5 could promote the synthesis of jasmonic acid (JA), a phytohormone that acts as a positive modulator in anthocyanin accumulation, by directly binding to the W-box element in the promoter of the JA biosynthesis-related gene VvLOX and enhancing its activities, and this activation was greatly enhanced by the VvWRKY5-VvMYBA1 protein complex. Collectively, our findings show that VvWRKY5 plays crucial roles in wounding-induced anthocyanin synthesis in grape and elucidates the transcriptional regulatory mechanism of wounding-induced anthocyanin accumulation.

Phenolic Acids and Flavonoids Play Important Roles in Flower Bud Differentiation in Mikania micrantha: Transcriptomics and Metabolomics

Mikania micrantha is a highly invasive vine, and its ability to sexually reproduce is a major obstacle to its eradication. The long-distance dissemination of M. micrantha depends on the distribution of seeds; therefore, inhibiting M. micrantha flowering and seed production is an effective control strategy. The number of blooms of M. micrantha differs at different altitudes (200, 900, and 1300 m). In this study, we used a combination of metabolomics and transcriptomics methods to study the patterns of metabolite accumulation in the flower buds of M. micrantha. Using LC-MS/MS, 658 metabolites were found in the flower buds of M. micrantha at three different altitudes (200, 900, and 1300 m). Flavonoids and phenolic acids were found to be the main differential metabolites, and their concentrations were lower at 900 m than at 200 m and 1300 m, with the concentrations of benzoic acid, ferulic acid, and caffeic acid being the lowest. The biosynthesis pathways for flavonoids and phenolic compounds were significantly enriched for differentially expressed genes (DEGs), according to the results of transcriptome analysis. The production of flavonoid and phenolic acids was strongly linked with the expressions of phenylalanine ammonia-lyase (PAL), caffeoyl-CoA O-methyltransferase (COMT), and 4-coumarate-CoA ligase (4CL), according to the results of the combined transcriptome and metabolome analysis. These genes' roles in the regulation of distinct phenolic acids and flavonoids during M. micrantha bud differentiation are still unknown. This study adds to our understanding of how phenolic acids and flavonoids are regulated in M. micrantha flower buds at various altitudes and identifies regulatory networks that may be involved in this phenomenon, offering a new approach for the prevention and management of M. micrantha.

The Influence of Solid and Liquid Systems In Vitro on the Growth and Biosynthetic Characteristics of Microshoot Culture of Spiraea betulifolia ssp. aemiliana

The paper focuses on the growth dynamics and biosynthetic characteristics of the microshoot culture of Spiraea betulifolia ssp. aemiliana obtained in vitro in agar-solidified and liquid media. Microshoots cultured in either type of media showed similar growth dynamics. The most active culture growth was observed from day 35 to day 60. A comparative analysis of the contents of flavonoids and phenol carboxylic acids showed a higher level of phenol carboxylic acids (5.3-6.84%) and a stronger 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity (half-maximal inhibitory concentration: 341 µg/mL) in S. betulifolia ssp. aemiliana microshoots grown in the liquid medium compared to the microshoots cultured in the solid medium. The flavonoid content of the cultured microshoot did not depend on the consistency of the medium. High-performance liquid chromatography (HPLC) was employed to study the profile and levels of phenolic compounds in microshoots, intact plants, and ex vitro-acclimated S. betulifolia ssp. aemiliana plants. The concentration of kaempferol glycosides was found to be higher in microshoots (1.33% in the solid medium, 1.06% in the liquid medium) compared to intact plants and ex vitro-acclimated plants. Thus, the microshoots of S. betulifolia ssp. aemiliana cultured in the liquid medium rapidly increase their biomass and are an inexpensive promising source of biologically active antioxidant substances, mainly phenol carboxylic acids and kaempferol glycosides.

Impact of trellis systems and rootstocks on global phenolic composition and antioxidant activity of ‘Isabel Precoce’ grapes produced during rainy seasons in semi-arid region of Brazil

Crop components, such as trellis systems, might affect solar radiation uptake by grapevines while others, such as rootstocks, influence the vigor of the scion. Proper management provides a suitable reproductive and vegetative balance that could influence the chemical composition of grapes. This study aimed to characterize the global phenolic composition and antioxidant activity of ‘Isabel Precoce’ grapes raised for juice, growing under different trellis systems and rootstocks, in rainy seasons, in semi-Arid conditions in Brazil. With a randomized block experimental design and split-split plots over time, the overhead trellis, lyre, and vertical shoot positioning systems and two rootstocks (‘IAC 572’ and ‘IAC 766’) in the harvest seasons of January-May, 2017 and January-May, 2018 were studied. Trellis systems, rootstocks, harvest seasons and their interactions affected the characteristics of the grapes. The treatments with equivalent responses in the seasons defined the specific characteristics of the grapes. The rootstock ‘IAC 766’ provided greater bunch weight and lower acidity to the ‘Isabel Precoce’ grapes, while ‘IAC 572’ induced higher soluble solids contents. In both seasons, there was lower variation in berry resistance to compression and polyphenol and anthocyanin contents in grapes from grapevines grown on an overhead trellis. In turn, the use of lyre provided high antioxidant activity by the ABTS●+ method in 2018. The highest antioxidant activity by the DPPH● method was due to the association of overhead trellis and ‘IAC 766’. With the use of the overhead trellis, equivalent phenolic compounds and antioxidant activity during the seasons resulted in a uniform quality.

Competition between anthocyanin and kaempferol glycosides biosynthesis affects pollen tube growth and seed set of Malus

Flavonoids play important roles in regulating plant growth and development. In this study, three kaempferol 3-O-glycosides were identified and mainly accumulated in flowers but not in leaves or fruits of Malus. In Malus, flower petal color is normally white, but some genotypes have red flowers containing anthocyanin. Anthocyanin biosynthesis appears to be in competition with kaempferol 3-O-glycosides production and controlled by the biosynthetic genes. The white flower Malus genotypes had better-developed seeds than the red flower genotypes. In flowers, the overexpression of MYB10 in Malus domestica enhanced the accumulation of anthocyanin, but decreased that of kaempferol 3-O-glycosides. After pollination the transgenic plants showed slower pollen tube growth and fewer developed seeds. Exogenous application of different flavonoid compounds suggested that kaempferol 3-O-glycosides, especially kaempferol 3-O-rhamnoside, regulated pollen tube growth and seed set rather than cyanidin or quercetin 3-O-glycosides. It was found that kaempferol 3-O-rhamnoside might regulate pollen tube growth through effects on auxin, the Rho of plants (ROP) GTPases, calcium and the phosphoinositides signaling pathway. With the inhibition of auxin transport, the transcription levels of Heat Shock Proteins (HSPs) and ROP GTPases were downregulated while the levels were not changed or even enhanced when blocking calcium signaling, suggesting that HSPs and ROP GTPases were downstream of auxin signaling, but upstream of calcium signaling. In summary, kaempferol glycoside concentrations in pistils correlated with auxin transport, the transcription of HSPs and ROP GTPases, and calcium signaling in pollen tubes, culminating in changes to pollen tube growth and seed set.

The spatio-temporal biosynthesis of floral flavonols is controlled by differential phylogenetic MYB regulators in Freesia hybrida

Floral flavonols play specific pivotal roles in pollinator attraction, pollen germination and fertility, in addition to other functions in vegetative organs. For many plants, the process of flavonol biosynthesis in late flower development stages and in mature flower tissues is poorly understood, in contrast to early flower development stages. It is thought that this process may be regulated independently of subgroup 7 R2R3 MYB (SG7 MYB) transcription factors. In this study, two FLS genes were shown to be expressed synchronously with the flower development-specific and tissue-specific biosynthesis of flavonols in Freesia hybrida. FhFLS1 contributed to flavonol biosynthesis in early flower buds, toruses and calyxes, and was regulated by four well-known SG7 MYB proteins, designated as FhMYBFs, with at least partial regulatory redundancy. FhFLS2 accounted for flavonols in late developed flowers and in the petals, stamens and pistils, and was targeted directly by non SG7 MYB protein FhMYB21L2. In parallel, AtMYB21 and AtMYB24 also activated AtFLS1, a gene highly expressed in Arabidopsis anthers and pollen, indicating the conserved regulatory roles of MYB21 against FLS genes in these two evolutionarily divergent angiosperm plants. Our results reveal a novel regulatory and synthetic mechanism underlying flavonol biosynthesis in floral organs and tissues which may be exploited to investigate supplementary roles of flavonols in flowers.

Genome-wide identification and comparative analysis of GST gene family in apple (Malus domestica) and their expressions under ALA treatment

Anthocyanins, a subclass of flavonoids, are synthesized at the cytoplasmic surface of the endoplasmic reticulum (ER), which then accumulate in vacuoles. Plant glutathione S-transferase (GST) genes are involved in anthocyanin transportation. Here, a total of 52, 42, 50, and 29 GST genes were identified from apple, pear, peach, and strawberry, respectively, through a comprehensive genome-wide survey. Based on phylogenetic analyses, the GST proteins of the four crops could be divided into the classes Phi, Tau, DHAR, TCHQD, and Lambda. The structure and chromosomal distribution of apple GST genes were further analyzed. The GST gene family expansion in apple likely occurred through tandem duplications, and purifying selection played a pivotal role in the evolution of GST genes. Synteny analysis showed strong microsynteny between apple and Arabidopsis/strawberry, but no microsynteny was detected between apple/strawberry/Arabidopsis and rice. Aminolevulinic acid (ALA), a key precursor of tetrapyrrole compounds, can significantly improve anthocyanin accumulation in fruits, Using RNA-seq and qRT-PCR analysis, we found that ALA treatment led to the differential expression of GST genes in apples. MdGSTF12 was strongly induced by ALA, suggesting that MdGSTF12 may play a role in ALA-induced anthocyanin accumulation. These results provide a detailed overview of GST genes in four Rosaceae species and indicate that GSTs are involved in ALA-induced anthocyanin accumulation.

TMT-Based Quantitative Proteomic Analysis Reveals the Crucial Biological Pathways Involved in Self-Incompatibility Responses in Camellia oleifera

Camellia oleifera is a valuable woody oil plant belonging to the Theaceae, Camellia oil extracted from the seed is an excellent edible oil source. Self-incompatibility (SI) in C. oleifera results in low fruit set, and our knowledge about the mechanism remains limited. In the present study, the Tandem mass tag (TMT) based quantitative proteomics was employed to analyze the dynamic change of proteins response to self- and cross-pollinated in C. oleifera. A total of 6,616 quantified proteins were detected, and differentially abundant proteins (DAPs) analysis identified a large number of proteins. Combined analysis of differentially expressed genes (DEGs) and DAPs of self- and cross-pollinated pistils based on transcriptome and proteome data revealed that several candidate genes or proteins involved in SI of C. oleifera, including polygalacturonase inhibitor, UDP-glycosyltransferase 92A1-like, beta-D-galactosidase, S-adenosylmethionine synthetase, xyloglucan endotransglucosylase/hydrolase, ABC transporter G family member 36-like, and flavonol synthase. Venn diagram analysis identified 11 proteins that may participate in pollen tube growth in C. oleifera. Our data also revealed that the abundance of proteins related to peroxisome was altered in responses to SI in C. oleifera. Moreover, the pathway of lipid metabolism-related, flavonoid biosynthesis and splicesome were reduced in self-pollinated pistils by the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. In summary, the results of the present study lay the foundation for learning the regulatory mechanism underlying SI responses as well as provides valuable protein resources for the construction of self-compatibility C. oleifera through genetic engineering in the future.

Structure-activity relationship studies of flavonol analogues on pollen germination

Flavonoids are polyphenolic compounds required in the fertilization process in many, if not all, plants. However, the exact biological mechanism(s) and the interacting proteins are unknown. To determine the characteristics important in activating or inhibiting the pollination sequence, a structure-activity relationship analysis of natural and synthetic flavonols was conducted. Flavonol analogues were synthesized through a modified "one-pot" procedure that utilized a Baker-Venkataraman type rearrangement and a Suzuki-Miyaura cross-coupling of a halo-flavonol with an organotrifluoroborate. Of the flavonols tested, kaempferol was the only compound to act as a full agonist. The other smaller, less sterically hindered flavonols (galangin, kaempferide, and 4'-methyl flavonol) acted as partial agonists. Larger more hydrophobic flavonol analogues (3'- and 4'-benzoyl, 3'- and 4'-phenyl, and 3'- and 4'-iodo flavonols) had minimal or no agonist activity. Competition assays between kaempferol and these minimally activating flavonols showed that these analogues inhibited the action of kaempferol in a manner consistent with noncompetitive antagonism. The results suggest that steric hindrance is the most important factor in determining a good agonist. Hydrogen bonding also had a positive effect as long as the substituent did not cause any steric hindrance.

The Jasmonate-ZIM-domain proteins interact with the WD-Repeat/bHLH/MYB complexes to regulate Jasmonate-mediated anthocyanin accumulation and trichome initiation in Arabidopsis thaliana

Jasmonates (JAs) mediate plant responses to insect attack, wounding, pathogen infection, stress, and UV damage and regulate plant fertility, anthocyanin accumulation, trichome formation, and many other plant developmental processes. Arabidopsis thaliana Jasmonate ZIM-domain (JAZ) proteins, substrates of the CORONATINE INSENSITIVE1 (COI1)-based SCF(COI1) complex, negatively regulate these plant responses. Little is known about the molecular mechanism for JA regulation of anthocyanin accumulation and trichome initiation. In this study, we revealed that JAZ proteins interact with bHLH (Transparent Testa8, Glabra3 [GL3], and Enhancer of Glabra3 [EGL3]) and R2R3 MYB transcription factors (MYB75 and Glabra1), essential components of WD-repeat/bHLH/MYB transcriptional complexes, to repress JA-regulated anthocyanin accumulation and trichome initiation. Genetic and physiological evidence showed that JA regulates WD-repeat/bHLH/MYB complex-mediated anthocyanin accumulation and trichome initiation in a COI1-dependent manner. Overexpression of the MYB transcription factor MYB75 and bHLH factors (GL3 and EGL3) restored anthocyanin accumulation and trichome initiation in the coi1 mutant, respectively. We speculate that the JA-induced degradation of JAZ proteins abolishes the interactions of JAZ proteins with bHLH and MYB factors, allowing the transcriptional function of WD-repeat/bHLH/MYB complexes, which subsequently activate respective downstream signal cascades to modulate anthocyanin accumulation and trichome initiation.

Comparative analysis of pistil transcriptomes reveals conserved and novel genes expressed in dry, wet, and semidry stigmas

Fertilization in angiosperms depends on a complex cellular "courtship" between haploid pollen and diploid pistil. These pollen-pistil interactions are regulated by a diversity of molecules, many of which remain to be identified and characterized. Thus, it is unclear to what extent these processes are conserved among angiosperms, a fact confounded by limited sampling across taxa. Here, we report the analysis of pistil-expressed genes in Senecio squalidus (Asteraceae), a species from euasterid II, a major clade for which there are currently no data on pistil-expressed genes. Species from the Asteraceae characteristically have a "semidry stigma," intermediate between the "wet" and "dry" stigmas typical of the majority of angiosperms. Construction of pistil-enriched cDNA libraries for S. squalidus allowed us to address two hypotheses: (1) stigmas of S. squalidus will express genes common to wet and dry stigmas and genes specific to the semidry stigma characteristic of the Asteraceae; and (2) genes potentially essential for pistil function will be conserved between diverse angiosperm groups and therefore common to all currently available pistil transcriptome data sets, including S. squalidus. Our data support both these hypotheses. The S. squalidus pistil transcriptome contains novel genes and genes previously identified in pistils of species with dry stigmas and wet stigmas. Comparative analysis of the five pistil transcriptomes currently available (Oryza sativa, Crocus sativus, Arabidopsis thaliana, Nicotiana tabacum, and S. squalidus), representing four major angiosperm clades and the three stigma states, identified novel genes and conserved genes potentially regulating pollen-pistil interaction pathways common to monocots and eudicots.

Genome-wide gene expression profiling reveals conserved and novel molecular functions of the stigma in rice

In angiosperms, the stigma provides initial nutrients and guidance cues for pollen grain germination and tube growth. However, little is known about the genes that regulate these processes in rice (Oryza sativa). Here, we generate rice stigma-specific or -preferential gene expression profiles through comparing genome-wide expression patterns of hand-dissected, unpollinated stigma at anthesis with seven tissues, including seedling shoot, seedling root, mature anther, ovary at anthesis, seeds 5 d after pollination, 10-d-old embryo, 10-d-old endosperm, and suspension-cultured cells by using both 57 K Affymetrix rice whole-genome array and 10 K rice cDNA microarray. A high reproducibility of the microarray results was detected between the two different technology platforms. In total, we identified 548 genes to be expressed specifically or predominantly in the stigma papillar cells of rice. Real-time quantitative reverse transcription-polymerase chain reaction analysis of 34 selected genes all confirmed their stigma-specific expression. The expression of five selected genes was further validated by RNA in situ hybridization. Gene Ontology analysis shows that several auxin-signaling components, transcription, and stress-related genes are significantly overrepresented in the rice stigma gene set. Interestingly, most of them also share several cis-regulatory elements with known stress-responsive genes, supporting the notion of an overlap of genetic programs regulating pollination and stress/defense responses. We also found that genes involved in cell wall metabolism and cellular communication appear to be conserved in the stigma between rice and Arabidopsis (Arabidopsis thaliana). Our results indicate that the stigmas appear to have conserved and novel molecular functions between rice and Arabidopsis.

Silencing the flavonoid pathway in Medicago truncatula inhibits root nodule formation and prevents auxin transport regulation by rhizobia

Legumes form symbioses with rhizobia, which initiate the development of a new plant organ, the nodule. Flavonoids have long been hypothesized to regulate nodule development through their action as auxin transport inhibitors, but genetic proof has been missing. To test this hypothesis, we used RNA interference to silence chalcone synthase (CHS), the enzyme that catalyzes the first committed step of the flavonoid pathway, in Medicago truncatula. Agrobacterium rhizogenes transformation was used to create hairy roots that showed strongly reduced CHS transcript levels and reduced levels of flavonoids in silenced roots. Flavonoid-deficient roots were unable to initiate nodules, even though normal root hair curling was observed. Nodule formation and flavonoid accumulation could be rescued by supplementation of plants with the precursor flavonoids naringenin and liquiritigenin. The flavonoid-deficient roots showed increased auxin transport compared with control roots. Inoculation with rhizobia reduced auxin transport in control roots after 24 h, similar to the action of the auxin transport inhibitor N-(1-naphthyl)phthalamic acid (NPA). Rhizobia were unable to reduce auxin transport in flavonoid-deficient roots, even though NPA inhibited auxin transport. Our results present genetic evidence that root flavonoids are necessary for nodule initiation in M. truncatula and suggest that they act as auxin transport regulators.

Contrasting strategies for UV-B screening in sub-Arctic dwarf shrubs

The content and distribution of UV-absorbing phenolic compounds was investigated in leaves of three species of Vaccinium co-existing at a site in north Sweden. Vaccinium myrtillus L., Vaccinium vitis-idaea L., and Vaccinium uliginosum L. exhibit markedly different strategies, in terms of localization and content of leaf phenolics and in their responses to UV-B enhancement. Plants were exposed to either ambient radiation or to enhancement of UV-B corresponding to 15% (clear sky) depletion of stratospheric ozone for approximately 10 years prior to commencement of this study. Vaccinium myrtillus contained the highest concentration of methanol-extractable UV-B-absorbing compounds, which was elevated in plants exposed to enhanced UV-B. Fluorescence and confocal laser scanning microscopy showed that these compounds were distributed throughout the leaf, and were particularly concentrated in chlorophyll-containing cells. In V. vitis-idaea, most phenolic compounds were cell wall-bound and concentrated in the walls of the epidermis; this pool increased in response to UV-B enhancement. It is suggested that these two plants represent extreme forms of two divergent strategies for UV-B screening, the different responses possibly being related to leaf longevity in the two species. The response of V. uliginosum was intermediate between the other two, with high concentrations of cell wall-bound phenolics in the epidermis but with this pool decreasing, and the methanol-soluble pool tending to increase, after exposure to enhanced UV-B. One explanation for this response is that this plant is deciduous, like V. myrtillus, but has leaves that are structurally similar to those of V. vitis-idaea.

Isolation and characterization of cDNAs expressed in the early stages of flavonol-induced pollen germination in petunia

Petunia (Petunia hybrida) pollen requires flavonols (Fl) to germinate. Adding kaempferol to Fl-deficient pollen causes rapid and synchronous germination and tube outgrowth. We exploited this system to identify genes responsive to Fls and to examine the changes in gene expression that occur during the first 0.5 h of pollen germination. We used a subtracted library and differential screening to identify 22 petunia germinating pollen clones. All but two were expressed exclusively in pollen and half of the clones were rare or low abundance cDNAs. RNA gel-blot analysis showed that the steady-state transcript levels of all the clones were increased in response to kaempferol. The sequences showing the greatest response to kaempferol encode proteins that have regulatory or signaling functions and include S/D4, a leucine-rich repeat protein, S/D1, a LIM-domain protein, and D14, a putative Zn finger protein with a heme-binding site. Eight of the clones were novel including S/D10, a cDNA only expressed very late in pollen development and highly up-regulated during the first 0.5 h of germination. The translation product of the S/D3 cDNA shares some features with a neuropeptide that regulates guidance and growth in the tips of extending axons. This study confirmed that the bulk of pollen mRNA accumulates well before germination, but that specific sequences are transcribed during the earliest moments of Fl-induced pollen germination.

white anther: A petunia mutant that abolishes pollen flavonol accumulation, induces male sterility, and is complemented by a chalcone synthase transgene

A mutation in an inbred line of petunia (Petunia hybrida) produces a reduction in the deep-purple corolla pigmentation and changes the anther color from yellow to white. In addition, the mutant, designated white anther (wha), is functionally male sterile. The inability of pollen from wha plants to germinate in vitro provides a physiological basis for the lack of seed set observed in self-crosses of the mutant. Biochemical complementation with nanomolar amounts of kaempferol, a flavonol aglycone, confirms that the inability of the wha pollen to germinate is due to a lack of this essential compound. Transgenic complementation with a functional ChsA (Chalcone synthase A) cDNA suggests that the genetic lesion responsible for the wha phenotype is in Chs, the gene for the first enzyme in the flavonol biosynthesis pathway. The genetic background of the parental line, as well as the pollen phenotype, allowed us to deduce that the wha mutation is in ChsA. To our knowledge, wha is the first induced, nontransgenic Chs mutant described in petunia, and analysis of the mutation confirms earlier molecular and genetic observations that only two Chs genes (A and J) are expressed in reproductive tissues and that they are differentially regulated in corolla and anther.

Survey of the Free and Conjugated Myricetin and Quercetin Content of Red Wines of Different Geographical Origins

Gradient reversed-phase HPLC was used to obtain quantitative estimates of the levels of free and conjugated myricetin and quercetin in 65 red wines from Italy, Chile, France, California, Australia, Bulgaria, Spain, Romania, New Zealand, Brazil, Morocco, and Hungary. The concentrations of total flavonols ranged from 4.6 to 41.6 mg L(-1). High total flavonol levels appear to be associated with the use of thick-skinned grape varieties, such as Cabernet Sauvignon, with a high skin:volume ratio, which were left to ripen fully in sunny conditions before harvest and which were extracted efficiently by modern methods of vinification. Some Chilean Cabernet Sauvignon wines contained up to 40 mg of total flavonols L(-1), which was higher than the levels detected in Cabernet Sauvignon from France, California, and Australia. The flavonol content of 1989 and 1990 Cabernet Sauvignon from Bulgaria was <6 mg L(-1). Chilean Cabernet Sauvignon, Merlot, and Pinot Noir all contained consistently higher concentrations of flavonols than their counterparts from different geographical regions.

Effect of three suppressors on the expression of powdery mildew resistance genes in barley

Three recessive mutagen-induced alleles that partially suppress the phenotypic expression of the semidominant powdery mildew resistance gene Mla12 have been studied. When each suppressor is present in homozygous condition, the infection type 0, conferred by gene Mla12 when homozygous, is changed to intermediate infection types. The three suppressor lines were crossed with seven near-isogenic lines with different powdery mildew resistance genes and one, M100, was crossed with nine additional lines. Seedlings of parents and from the F1and F2generations were tested with powdery mildew isolates that possessed the appropriate avirulence and virulence genes. The segregation of phenotypes in the F2generation disclosed that the three suppressors affected the phenotypic expression of three resistance genes, whereas that of four resistance genes remained unaffected. The suppressor in mutant M100 affected the phenotypic expression of 9 of the 10 additional resistance genes present. It is suggested that the three suppressors are mutationally modified genes involved in host defence processes. This implies that different resistance genes employ different, but overlapping, spectra of defence processes, or signal transduction pathways. Key words : barley, Hordeum vulgare, powdery mildew, Erysiphe graminis hordei, mutation, resistance, suppressor.

Plant disease resistance genes: unravelling how they work

Resistance (R) genes confer on a plant the ability to defend itself following microbial attack. Each R gene exhibits an extreme specificity of action and is only effective against a microbe that has the corresponding functional avirulence (Avr) gene. This article reviews the strategies and experimental approaches deployed to understand the molecular events underlying the specificity of action of various tomato Cf resistance genes that results in incompatibility to the fungal pathogen Cladosporium fulvum. Topics covered include the clustering of Cf genes, the biology of Cf-dependent incompatibility, the map-based and transposon tagging approaches used to clone the Cf-2 and Cf-9 genes, respectively, identification by mutagenesis of other plant loci required for full Cf-9 mediated resistance, the expression of a functional Avr9 gene in planta and its lethal consequences to Cf-9 containing plants, the physiological and molecular host responses to C. fulvum and AVR elicitor challenges and some genetic approaches to ascertain the crucial components of the defense response. Key words: Cladosporium fulvum, Lycopersicon esculentum, tomato leaf mold, Cf resistance genes, fungal avirulence genes, plant defense responses.