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We are beginning to understand the biochemical nature of the genes that Gregor Mendel studied in his classic experiments with garden peas. This paper shows where Mendel's genes are located on the pea chromosome map, discusses the mutations involved in some of these genes, and shows how they can be used to teach classical genetics and the nature of the gene. Key Words: Gregor Mendel; garden peas; meiosis; genes code for proteins; enzymes determine phenotype; biochemical basis of Mendel's genes., It has been nearly 150 years since Gregor Mendel published his work on the genetics of garden peas (Mendel, 1866). We can now look at this seminal work, available in [...]

Although most land plants are hosts for arbuscular mycorrhizal fungi (AMF), a small number of plant families are arbuscular mycorrhizal (AM) nonhosts. There are indications that strigolactone levels in root exudates of AM nonhost plants are lower than in AM host plants, and it has been shown that in the strigolactone-deficient rmsl mutant (ccd8) of the AM host plant pea, the AMF colonization of roots is highly reduced. Application of the synthetic strigolactone analogue GR24 to this strigolactones-deficient mutant restored AMF colonization of roots. Our objective was to determine whether the application of GR24 to AM nonhost plants can affect their susceptibility to AMF. To test whether GR24 affects AMF colonization in our experimental system, we added GR24 to the strigolactone-deficient pea ccd8 mutant. Application of GR24 increased AMF colonization in the pea mutant to a similar level as in the pea wild type with normal strigolactone levels, showing clearly that in our experimental setup, application of the GR24 positively affects AMF colonization in strigolactone-deficient plants. Observation of cleared roots after application of GR24 to four AM nonhost plant species inoculated with the AMF Glomus intraradices showed that colonization did not occur. Key words: arbuscular mycorrhiza, AM nonhost plants, GR24, strigolactones. Bien que la plupart des plantes terrestres constituent des hotes pour les champignons mycorhiziens arbusculaires (CMA), un petit nombre de familles de plantes ne sont pas des hotes pour les mycorhizes arbusculaire (non hotes MA). Il y a des indications que les teneurs en strigolactones dans les exsudats des plantes non hotes MA seraient moins grandes que chez les plantes hotes MA, et on a egalement demontre que le mutant strigolactones-deficient-rmsl (ccd8) du pois plante hote MA, qu'il y a une forte reduction de la colonisation racinaire MA. L'application d'un analogue de la strigolactone GR24 sur ce mutant strigolactones-deficient restaure la colonisation MA des racines. Les auteurs ont cherche a determiner si l'application de GR24 aux plantes non hotes MA peut affecter leur susceptibilite aux CMA. A cette fin, ils ont verifie si le GR24 affecte la colonisation MA en utilisant leur systeme experimental et en mettant le mutant strigolactone- deficient ccd8 du pois en presence de GR24. L'application de GR24 a augmente la colonisation MA chez le pois mutant, au meme degre que chez le type sauvage du pois, possedant des teneurs normales en strigolactones, demontrant ainsi clairement que dans ce dispositif experimental le GR24 affecte positivement la colonisation MA chez les plants strigolactones- deficients. L'observation de racines eclaircies, apres l'application de GR24, sur quatre especes de plantes non hotes MA inoculees avec le CMA Glomus intraradices, montre que la colonisation n'a pas eu lieux. Mots-cles : mycorhizes arbusculaires, plante AM non hotes, GR24, strigolactones. [Traduit par la Redaction], Introduction Most land plants are arbuscular mycorrhizal fungi (AMF) host plants; however, some plant families (e.g., the Brassicaceae and the Chenopodiaceae) are nonhosts for AMF. Lupinus spp. are exceptions in [...]

Susceptibility to black spot [caused by Mycosphaerella pinodes (Berk. and Blox.) Vestergr.] and weak stem strength in field pea (Pisum sativum L.) are major restrictions to yield, seed quality, and ease of harvest. Previous studies have established that additive genetic variance is present for both traits, and that stem strength is strongly associated with a field test of compressed stem thickness at the base of the stem. This study aimed to improve these two complex traits simultaneously by recurrent selection. Heritabilities and responses to selection for resistance to black spot and stem strength were evaluated during two cycles of recurrent selection after intercrossing diverse genotypes. Response to selection was indicated by a reduction of 10% in the mean black spot leaf disease in the [F.sub.2] of cycle 2 compared with the [F.sub.2] of cycle 1, when considered as a percentage of the mean of cycle 1 parents in the same trials. Likewise, there was a 15% increase in stem strength, based on the mean compressed stem thickness in the [F.sub.2] of cycle 2 compared with the [F.sub.2] of cycle 1. Broad sense heritability for resistance to black spot leaf disease was moderate (H = 0.63 [+ or -] 0.35 across cycles 1 and 2) and for compressed stem thickness was also moderate (H = 0.66 [+ or -] 0.34). Genetic gains were realized for both traits simultaneously in the first two cycles and were predicted to be rapid over the next five to six cycles based on a random mating quantitative genetics model.

Floral zygomorphy (flowers with bilateral symmetry) has multiple origins and typically manifests two kinds of asymmetries, dorsoventral (DV) and organ internal (IN) asymmetries in floral and organ planes, respectively, revealing the underlying key regulators in plant genomes that generate and superimpose various mechanisms to build up complexity and different floral forms during plant development. In this study, we investigate the loci affecting these asymmetries during the development of floral zygomorphy in pea (Pisum sativum L.). Two genes, LOBED STANDARD 1 (LST1) and KEELED WINGS (K), were cloned that encode TCP transcription factors and have divergent functions to constitute the DV asymmetry. A previously undescribed regulator, SYMMETRIC PETALS 1 (SYP1), has been isolated as controlling IN asymmetry. Genetic analysis demonstrates that DV and IN asymmetries could be controlled independently by the two kinds of regulators in pea, and their interactions help to specify the type of zygomorphy. Based on the genetic analysis in pea, we suggest that variation in both the functions and interactions of these regulators could give rise to the wide spectrum of floral symmetries among legume species and other flowering plants. symmetric petal | dorsoventral asymmetry | organ internal asymmetry | KEELED WINGS | LOBED STANDARD 1

For >40 years, geneticists and science historians have appealed to the tetrad-pollen model as an explanation of the bias toward expectation in Mendel's data, albeit without experimental support. Our experiments demonstrate that pollen sampling during self-pollination in pea conforms to the binomial distribution with no evidence of a tetrad-pollen effect.

Sequence diversity of 39 dispersed gene loci was analyzed in 48 diverse individuals representative of the genus Pisum. The different genes show large variation in diversity parameters, suggesting widely differing levels of selection and a high overall diversity level for the species. The data set yields a genetic diversity tree whose deep branches, involving wild samples, are preserved in a tree derived from a polymorphic retrotransposon insertions in an identical sample set. Thus, gene regions and intergenic 'junk DNA' share a consistent picture for the genomic diversity of Pisum, despite low linkage disequilibrium in wild and landrace germplasm, which might be expected to allow independent evolution of these very different DNA classes. Additional lines of evidence indicate that recombination has shuffled gene haplotypes efficiently within Pisum, despite its high level of inbreeding and widespread geographic distribution. Trees derived from individual gene loci show marked differences from each other, and genetic distance values between sample pairs show high standard deviations. Sequence mosaic analysis of aligned sequences identifies nine loci showing evidence for intragenic recombination. Lastly, phylogenetic network analysis confirms the non-treelike structure of Pisum diversity and indicates the major germplasm classes involved. Overall, these data emphasize the artificiality of simple tree structures for representing genomic sequence variation within Pisum and emphasize the need for fine structure haplotype analysis to accurately define the genetic structure of the species.

Resistance to Mycosphaerella pinodes in field pea (Pisum sativum L) is a quantitative trait, and expression of resistance is substantially influenced by environment. The disease reaction to mycosphaerella blight of four crosses ([F.sub.2:4] and [F.sub.2:5] populations) was assessed in field trials at Vegreville, AB, Canada. Broad-sense heritability of resistance was quite high (0.62-0.81). Narrow-sense (realized) heritability was moderate (0.43-0.57), indicating that additive genetic factors contributed substantially to the resistance phenotype. Significant improvement in resistance among the lines developed from selected individuals indicates that genetic improvement based on progeny testing would be effective. This study demonstrated that resistance to M. pinodes can be improved through progeny selection from crosses of the most resistant lines.

Abstract: Pea (Pisum sativum L.) has a genome of about 4 Gb that appears to share conserved synteny with model legumes having genomes of 0.2-0.4 Gb despite extensive intergenic expansion. [...]

Mutants that retain greenness of leaves during senescence are known as 'stay-green' mutants. The most famous stay-green mutant is Mendel's green cotyledon pea, one of the mutants used in determining the law of genetics. Pea plants homozygous for this recessive mutation (known as i at present) retain greenness of the cotyledon during seed maturation and of leaves during senescence. We found tight linkage between the I locus and stay-green gene originally found in rice, SGR. Molecular analysis of three i alleles including one with no SGR expression confirmed that the I gene encodes SGR in pea. Functional analysis of sgr mutants in pea and rice further revealed that leaf functionality is lowered despite a high chlorophyll a (Chl a) and chlorophyll b (Chl b) content in the late stage of senescence, suggesting that SGR is primarily involved in Chi degradation. Consistent with this observation, a wide range of Chl-protein complexes, but not the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) large subunit, were shown to be more stable in sgr than wild-type plants. The expression of OsCHL and NYC1, which encode the first enzymes in the degrading pathways of Chl a and Chl b, respectively, was not affected by sgr in rice. The results suggest that SGR might be involved in activation of the Chl-degrading pathway during leaf senescence through translational or posttranslational regulation of Chl-degrading enzymes. locus | pea | rice | senescence | stay green

Mycosphaerella blight, caused mainly by Mycosphaerella pinodes (Berk. and Blox.) Vestergren, is the most important foliar disease on field pea (Pisum sativum L.) in western Canada. A quantitative trait analysis of resistance to M. pinodes was undertaken on five crosses with reciprocals of P. sativum to examine broad-sense ([H.sup.2]) and narrow-sense ([h.sup.2]) heritability, minimum number of genes involved (MNG), mid-parent heterosis (MPH), cytoplasmic inheritance, and epistasis. Mean [H.sup.2] was 0.75 (range 0.67-0.80) and mean [h.sup.2] was 0.59 (range 0.41-0.70), indicating that additive variance is important and that improvement in resistance can be achieved through breeding. Mean MNG was 2.16 genes (range 0.06-6.22), indicating that genes for resistance differed among parent lines. Mean MPH was 50% (range 47-57%), indicating that heterosis did not influence the expression of resistance to M. pinodes. There was no difference between the mean of any [F.sub.1] population and its reciprocal, indicating lack of maternal inheritance. The mean of the epistatic points was -0.01 (range -0.1 to 0.12), indicating that epistasis was not important in these crosses. These results will further the understanding of the natural genetic diversity for disease resistance to M. pinodes in P. sativum.

Abstract: Three copies of the gene that encodes cytochrome c oxydase subunit Vb were isolated from the pea (PscoxVb-1, PscoxVb-2, and PscoxVb-3). Northern Blot and reverse transcriptase-PCR analyses suggest that [...]

Comprehensive assessments of germplasm collections of field pea (Pisum sativum L.) have failed to identify any accessions that are highly resistant to Mycosphaerella blight, caused by Mycosphaerella pinodes. In the present study, the broad-sense heritability of resistance to M. pinodes was studied on 558 pea genotypes in a detached-leaf assay and in field trials over 2 yr. in addition, analysis of covariance in disease reaction between the two assessment methods was examined. Only a few genotypes displayed relatively high levels of resistance, and as expected, no complete resistance was observed. The pattern of differences in reaction to M. pinodes among the genotypes demonstrates that resistance is quantitative and moderately heritable. Broad-sense heritability was higher in the detached-leaf assays than in the field trials, likely because of more environmental variance in the field. Covariance between repetitions of the detached leaf assays was not significant but was significant between the field tests. This indicates that detached-leaf assessments are more reliable for assessment of large numbers of accessions.

Sequences flanking 73 insertions of the retrotransposon PDR1 have been characterized, together with an additional 270 flanking regions from one side alone, from a diverse collection of Pisum germ plasm. Most of the identified flanking sequences are repetitious DNAs but more than expected (7%) lie within nuclear gene protein-coding regions. The approximate age of 52 of the PDR1 insertions has been determined by measuring sequence divergence among LTR pairs. These data show that PDR1 transpositions occurred within the last 5 MY, with a peak at 1-2.5 MYA. The insertional polymorphism of 68 insertions has been assessed across 47 selected Pisum accessions, representing the diversity of the genus. None of the insertions are fixed, showing that PDR1 insertions can persist in a polymorphic state for millions of years in Pisum. The insertional polymorphism data have been compared with the age estimations to ask what rules control the proliferation of PDR1 insertions in Pisum. Relatively recent insertions (< ~1.5MYA) tend to be found in small subsets of the Piston accessions set, 'middle-aged' insertions (between ~1.5 and 2.5 MYA) vary greatly in their occurrence, and older insertions (> ~2.5 MYA) are mostly found in small subsets of Pisum. Finally, the average age estimate for PDRI insertions, together with an existing data set for PDR1 retrotransposon SSAP markers, has been used to derive an estimate of the effective population size for Pisum of ~7.5 X [10.sup.5].