ScORK17, a transmembrane receptor-like kinase predominantly expressed in ovules is involved in seed development

The mRNA expression of the Solanum chacoense Ovule Receptor Kinase 17 (ScORK17), a receptor kinase of the LRR-VI subfamily, is highly specific to the female reproductive tissues. No LRR-VI subfamily members in any plant species have yet been attributed a function. A phylogenetic tree inferred using the kinase domain of LRR-VI subfamily members separated the family into two clades: one containing an average of 8.2 LRR per protein and a second clade containing an average of 2.7. In situ hybridization analyses showed that the ScORK17 signal was mainly detected in the single ovule integument and in the endothelium. Transient expression analysis also revealed that ScORK17 was N-glycosylated in planta. Overexpression of ScORK17 in S. chacoense did not produce plants with an altered phenotype. However, when heterologous transformation was performed with a full-length ScORK17 clone in A. thaliana, the resulting transgenic plants showed reduced seed set, mainly due to aberrant embryo sac development, thus supporting a developmental role for ScORK17 in ovule and seed development.     

Identification of pistil-specific proteins associated with three self-incompatibility alleles in Solanum chacoense

Summary Pistil proteins associated with three different S-alleles of the self-incompatibility locus (S locus) in Solanum chacoense have been identified which cosegregated with their respective S alleles in a series of genetic crosses involving six S. chacoense plants, their F₁ progeny, and backcrosses. The molecular weights of these three S-allele-associated proteins, designated S₁ S₂, and S₃, were 29 kDa, 30 kDa, and 31 kDa, respectively. They were all basic proteins with a similar pI of approximately 8.6. They have been found only in the stigma and style of the pistil where their maximum synthesis was reached at one day before anthesis. Their rate of synthesis in both self- and cross-pollinated pistils was the same as that in the unpollinated pistil until 2 days after pollination.On sabbatical leave from Laboratoire de Genetique et Physiologie du Developpement des Plantes, C.N.R.S., F-91190 Gifsur-Yvette, France     

Examination of the hybrid origin of the wild potato Solanum ruiz-lealii Brücher

The common potato, tetraploid Solanum tuberosum spp. tuberosum L. (tbr), has a narrow genetic base but a large number of related tuber-bearing species that harbor genetic diversity for agronomic characters. The taxonomic status of Solanum ruiz-lealii Brücher (rzl), a diploid species endemic to Mendoza province, Argentina, is controversial. It has been described as a new species of non-hybrid origin and as a natural hybrid between S. kurtzianum Bitt. & Wittm. (ktz) and S. chacoense Bitt. (chc). The hypothesis of the hybrid origin of rzl is examined systematically for the first time by phenetic analyses of morphological and molecular (SSR markers) data, and cytological analyses of interspecific hybrids. The morphological, cytological and molecular data are congruent, and suggest that rzl is not a recent natural hybrid between the ktz and the chc populations studied but has probably originated by divergence of chc, or by hybridization between chc and another taxon.     

Mapping of resistance to the potato cyst nematode Globodera rostochiensis from the wild potato species Solanum vernei

A population of diploid potato (Solanum tuberosum) was used for the genetic analysis and mapping of a locus for resistance to the potato cyst nematode Globodera rostochiensis, introgressed from the wild potato species Solanum vernei. Resistance tests of 108 genotypes of a F₁ population revealed the presence of a single locus with a dominant allele for resistance to G. rostochiensis pathotype Ro1. This locus, designated GroV1, was located on chromosome 5 with RFLP markers. Fine-mapping was performed with RAPD and SCAR markers. The GroV1 locus was found in the same region of the potato genome as the S. tuberosum ssp. andigena H1 nematode resistance locus. Both resistance loci could not excluded to be allelic. The identification of markers flanking the GroV1 locus offers a valuable strategy for marker-assisted selection for introgression of this nematode resistance.Abbreviations BSA bulked segregant analysis - RAPD random-amplified polymorphic DNA - RFLP restriction fragment length polymorphism - SCAR sequence-characterized amplified region     

RFLP analysis of the wild potato species,Solanum acaule Bitter (Solanum sect. Petota)

Summary Intraspecific variation of a wild potato species, Solanum acaule Bitt., was analyzed by RFLPs of genomic DNA. One hundred and five accessions were selected throughout the distribution area, including all subspecies, i.e., ssp. albicans (hexaploid), ssp. punae (tetraploid), ssp. acaule (tetraploid) and ssp. aemulans (tetraploid). Twenty-seven low-copy DNA clones (probes) were Southern hybridized with EcoRI, EcoRV, HindIII, and XbaI digests of total DNA of all accessions. In total, 238 RFLPs were detected from 94 enzyme x probe combinations. Among them, 49 RFLPs were specific to ssp. albicans, suggesting that the additional third genome is distinct from its two other genomes. RFLPs between and within subspecies were analyzed by principal component analysis. DNA similarities between subspecies coincided with a former taxonomic treatment in the sense that ssp. albicans is the most distantly related to ssp. acaule and ssp. aemulans is distantly related. Subspecies acaule and ssp. punae were indistinguishable. In addition, RFLPs could be used to distinguish groups within subspecies. Subspecies aemulans, confined to Argentina, was divided into two populations, one from the province of La Rioja and the other from the province of Jujuy. In ssp. acaule, some accessions from the southernmost distribution area were clearly distinguishable, while the others varied continuously, showing a geographical cline from Peru to Argentina.Reference to a specific brand or firm name does not constitute endorsement by the US Department of Agriculture over others of similar nature not mentioned     

Characterization of a fertilization-induced and developmentally regulated plasma-membrane aquaporin expressed in reproductive tissues,in the wild potato Solanum chacoense Bitt

Fertilization triggers a unique and complex developmental program leading to embryogenesis and seed set. Growth and differentiation are accompanied by rapid metabolic changes as well as massive cellular reorganization inside the fertilized ovule. Using differential display to isolate genes involved in pollen-pistil interactions and early fertilization events, we isolated from Solanum chacoense Bitt. a fertilization-induced plasma-membrane intrinsic protein of the PIP2 family that is predominantly expressed in pistil and anthers tissues. Major intrinsic proteins (MIPs) consist of a large family of highly conserved membrane-spanning proteins that are mainly represented in plants by the aquaporins. Aquaporins, mainly of the PIP and TIP type, have been shown in many species to serve as water channels. In S. chacoense the ScPIP2a mRNA is developmentally regulated during anthesis, with mRNA levels gradually decreasing as the pistil reaches maturity. In flowers, strongest expression was observed in elongating styles, in stamens, and transiently in ovules following fertilization. In styles, maximal expression levels correlated with phases of rapid style elongation and with the formation of epidermal papillae. ScPIP2a mRNA was also strongly expressed in developing fruit, consistent with a role in cell expansion during maturation and development.     

Large differences in amino acid sequences among ferredoxins from several species of genus Solanum

The complete amino acid sequences of [2Fe-2S] ferredoxins from four species of genus Solanum (S. nigrum, S. lyratum, S. indicum, and S. abutiloides) were determined by automated Edman degradation of the entire S-carboxymethylcysteinyl proteins and of the peptides obtained by enzymatic digestion. The amino acid sequences of these four ferredoxins differed from each other by 12-19, whereas 0-4 differences have been observed among ferredoxins from plants in the same genus and 14-40 differences were seen between different families. This suggests that these Solanum plants are distantly related to each other taxonomically.     

A comparative proteome and phosphoproteome analysis of differentially regulated proteins during fertilization in the self-incompatible species Solanum chacoense Bitt

We have used 2-DE for a time-course study of the changes in protein and phosphoprotein expression that occur immediately after fertilization in Solanum chacoense. The phosphorylation status of the detected proteins was determined with three methods: in vivo labeling, immunodetection, and phosphoprotein-specific staining. Using a pI range of 4-7, 262 phosphorylated proteins could be mapped to the 619 proteins detected by Sypro Ruby staining, representing 42% of the total proteins. Among these phosphoproteins, antibodies detected 184 proteins from which 78 were also detected with either of the other two methods (42%). Pro-Q Diamond phosphoprotein stain detected 111 proteins, of which 76 were also detected with either of the other two methods (68%). The 32P in vivo labeling method detected 90 spots from which 78 were also detected with either of other two methods (87%). On comparing before and after fertilization profiles, 38 proteins and phosphoproteins presented a reproducible change in their accumulation profiles. Among these, 24 spots were selected and analyzed by LC-MS/MS using a hybrid quadrupole-TOF (Q-TOF) instrument. Peptide data were searched against publicly available protein and EST databases, and the putative roles of the identified proteins in early fertilization events are discussed.     

Purification of a polyphenol oxidase isoform from potato (Solanum tuberosum) tubers

A different expression pattern of polyphenol oxidases has been observed during storage in cultivars of potato (Solanum tuberosum L.) featuring different length of dormancy: a short-dormant cultivar showed, at the end of the dormancy, both the highest polyphenol oxidase activity and the largest number of enzyme isoforms. An isoform of polyphenol oxidase isolated at the end of the physiological dormancy from a short-dormant cultivar has been purified to homogeneity by means of column chromatography on phenyl Sepharose and on Superdex 200. The purification factor has been determined equal to 88, and the molecular mass of the purified isoform has been estimated to be 69 and 340 kDa by SDS polyacrylamide gel electrophoresis and gel filtration on Superdex 200, respectively, indicating this PPO isoform as a multimer. The corresponding zymogram features a diffused single band at the cathodic region of the gel and the pI of this polyphenol oxidase has been calculated equal to 6.5.     

Cloning and functional analysis of a cDNA encoding a starch synthase from potato (Solanum tuberosum L.) that is predominantly expressed in leaf tissue

Three isoforms of starch synthase (SS) were shown to be present in soluble potato tuber extracts by activity staining after native gel electrophoresis. A cDNA encoding SSI from rice was used as a probe to clone a corresponding cDNA from potato. The deduced amino acid sequence identified the protein as an SS from potato with an M_r of 70.6 kDa for the immature enzyme including its transit peptide. This novel isoform was designated SSI. An analysis of the expression pattern of the gene indicated that SSI is predominantly expressed in sink and source leaves, and, to a lower extent in tubers. In several independent transgenic potato lines, where the expression of SSI was repressed using the antisense approach, the activity of a specific SS isoform was reduced to non-detectable levels as determined through activity staining after native gel electrophoresis. The reduction in the amount of this isoform of SS did not lead to any detectable changes in starch structure, probably due to the fact that this isoform only represents a minor activity in potato tubers. Received: 19 August 1998 / Accepted: 17 December 1998     

A reexamination of infraspecific taxa of a wild potato,Solanum microdontum (Solanum sect.Petota:Solanaceae)

Current taxonomic interpretations ofSolanum microdontum Bitter partition the species into two or three infraspecific taxa, variously recognized as subspecies or varieties. The present study reexamines these taxa using morphological data from four individuals each of 69 accessions from most of the range of the species, planted in a common field plot. Our results show that the character states used to recognize infraspecific taxa inS. microdontum often vary within accessions and have no correlation with geography. We conclude that past hypotheses have used typological concepts and that infraspecific taxa are not warranted. This study questions other hypotheses of infraspecific taxa in sect.Petota.     

An S-locus receptor-like kinase plays a role as a negative regulator in plant defense responses

Plant cells often use cell surface receptors to sense environmental changes and then transduce external signals via activated signaling pathways to trigger adaptive responses. In Arabidopsis, the receptor-like protein kinase (RLK) gene family contains more than 600 members, and some of these are induced by pathogen infection, suggesting a possible role in plant defense responses. We previously characterized an S-locus RLK (CBRLK1) at the biochemical level. In this study, we examined the physiological function of CBRLK1 in defense responses. CBRLK1 mutant and CBRLK1-overexpressing transgenic plants showed enhanced and reduced resistance against a virulent bacterial pathogen, respectively. The altered pathogen resistances of the mutant and overexpressing transgenic plants were associated with increased and reduced induction of the pathogenesis-related gene PR1, respectively. These results suggest that CBRLK1 plays a negative role in the disease resistance signaling pathway in Arabidopsis.     

Characterization of Resistance in a Somatic Hybrid of Solanum bulbocastanum and S. tuberosum,to Meloidogyne chitwoodi

A somatic hybrid, CBP-233, between resistant Solanum bulbocastanum (SB-22) and susceptible S. tuberosum (R4) was tested for resistance to Meloidogyne chitwoodi race 1. One week after inoculation, only 0.04-0.4% of the initial inoculum (Pi, 5,000 eggs) as second stage-juveniles infected SB-22 and CBP-233 root systems, compared to 2% in R4. After 8 weeks, the number of M. chitwoodi in SB-22 and CBP-233 roots remained lower (0.3-1.5% of Pi) compared to R4, which increased from 2% to ca. 27%. Development of M. chitwoodi was delayed on SB-22 and CBP-233 by at least 2 weeks, and only half of the infective nematodes established feeding sites and matured in resistant clones compared to 99% in susceptible R4. Necrotic tissue surrounded nematodes that failed to develop in SB-22 and CBP-233. The reproductive factor (ratio of final number of eggs recovered from roots to Pi) was <0.01 for both SB-22 and CBP-233 and 46.8 for R4. Delaying inoculation of CBP-233 from 1 to 3 months after planting did not increase the chance or rate of tuber infection. Only a few M. chitwoodi developed to maturity on CBP-233 tubers and deposited a small number of eggs. SB-22 rarely produced tubers in these experiments, and like CBP-233 were resistant to M. chitwoodi. It appeared that the mechanisms of resistance to M. chitwoodi in roots and tubers of CBP-233 are similar.     

Fertile somatic hybrids of Solanum species: RFLP analysis of a hybrid and its sexual progeny from crosses with potato

Summary Restriction fragment length polymorphism (RFLP) markers were used to distinguish the chromosomes of Solanum brevidens from those of potato (S. tuberosum) in a fertile somatic hybrid. The hybrid had markers that account for all 24 chromosome arms from each parent, indicating that the hybrid contained at least one copy of each chromosome from each parent. The markers were then used to follow segregation of chromosomes in sexual progeny that resulted from a cross of the somatic hybrid with the potato cultivar Katahdin. Approximately 10% of the sexual progeny lacked one or more of the markers specific to S. brevidens. No one chromosome or marker appeared to be lost preferentially. This infrequent absence of a chromosome marker derived from the wild parent could be explained by intergenomic pairing and recombination. The loss of a marker band for chromosome 8, coupled with the retention of two flanking markers, suggested that a small region of DNA was deleted during regeneration of the somatic hybrid. These results show the value of RFLP analysis when applied to somatic hybrids and their progeny. Clearly, RFLPs will be useful for following the DNA from wild species during its introgression into potato cultivars.Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products or vendors that may also be suitable     

Genetic analysis of anther and leaf disc culture in two clones of Solanum chacoense Bitt. and their reciprocal hybrids

Two diploid clones of self-incompatible Solanum chacoense Bitt. with androgenetic ability were tested for anther and leaf disc culture response together with eight of their reciprocal F1 hybrids. Large differences were found among genotypes in frequency of anther induction as well as in the phase of plant regeneration. Anthers harvested in June showed a significantly higher percentage of response (17.5%) at the induction phase than those collected in July (13.8%) or August (12.7%). The lowest induction frequency was observed in May (7.3%). By contrast, plant regeneration from induced anthers did not vary during this time. Genotypic differences were also observed in leaf disc response. The two parental clones and two of their hybrids failed to produced any shoots. Among the remaining genotypes, two had only sporadic occurrence of shoot formation, two gave an intermediate response (15% and 24% of their discs carried shoots), whereas the discs of the two remaining genotypes responded well to culture (68% and 77%). The genetic analysis performed on the reciprocal hybrids revealed that a positive significant correlation existed between anther induction and leaf disc response (Spearman's r=0.82; p=0.01). This suggests that, under our conditions, these two aspects of tissue culture might share a common system of genetic control. Estimates of broad sense heritabilities, for leaf disc culture, 83% were obtained and the number of effective factors involved in the control of tissue culture response, indicated a relatively simple genetic control. Finally, considering the potentialities opened by the use of RFLP analysis, it might be possible to find probes that are linked with genes involved in tissue culture competence.