Báo cáo khoa học: "Differences of genetic variation based isozymes of primary and secondary metabolism in Quercus petraea"

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Original article Differences of genetic variation based isozymes of primary and secondary metabolism on * in Quercus petraea A Zanetto, A Kremer, T Labbé INRA, laboratoire de génétique et d’amélioration des arbres forestiers, BP 45, 33611 Gazinet Cedex, France Summary — The genetic variation among 18 populations of Q petraea was investigated, by study- ing the variability of 6 enzyme-coding loci. The populations were distributed over the range of the species. Three of the enzymes studied are involved in the primary metabolism (group I), while the re- maining 3 are part of the secondary metabolism (group II). With respect to enzymes of group I, pop- ulations from the western part of the range showed higher observed and expected heterozygosities than eastern and extreme southern populations. Differentiation among populations was low; G val- st ues varied between 2 and 5% depending upon the locus investigated. Based upon enzymes of group I, differentiation among populations of the central part of the range was of the same magni- tude as that among populations of the total range for enzymes of group I. However, levels of differ- entiation increased for enzymes of group II. allozyme / heterozygosity / genetic differentiation / Q petraea Résumé — Variabilité génétique des enzymes du métabolisme primaire et secondaire chez le chêne sessile. La variabilité génétique de Quercus petraea a été étudiée sur un échantillon de 18 populations venant de l’ensemble de l’aire naturelle. L’analyse portait sur 6 locus correspondant à 6 enzymes, dont 3 étaient impliquées dans le métabolisme primaire (groupe I) et les 3 autres dans le métabolisme secondaire (groupe II). Les populations occidentales sont plus variables (hétérozygotie observée et théorique) que les populations orientales ou de l’extrémité méridionale de l’aire de distri- bution. Ces résultats ne s’appliquent qu’aux enzymes du groupe I. La différenciation entre popula- tions reste très faible; les valeurs de G varient de 2 à 5% selon les enzymes. Pour les enzymes du st groupe I, la différenciation entre les populations du centre de l’aire de distribution est du même ordre de grandeur que celle entre les populations de l’ensemble de l’aire. Par contre, dans le cas des en- zymes du groupe II la différenciation augmente avec la taille de l’échantillon des populations. allozyme / hétérozygotie / différenciation génétique / Q petraea * The research has been EEC grant MA1B/009-0016, 0037-0038 ’Genetics and supported by a breeding of oaks’.
INTRODUCTION MATERIALS AND METHODS Eighteen populations were sampled over the natu- The natural range of sessile oak (Quercus ral range (fig 1). This is part of a range-wide study petraea (Matt) Liebl) extends over the en- on gene diversity of Q petraea. Seeds were col- tire continent of Europe, with the exception lected in each stand on the basis of a systematic of the Mediterranean region and northern grid system comprised of 30-50 collection points. Scandinavia (Camus, 1934-1954). Partial Seeds were collected 100-200 at each point and information on geographic variation of the bulked for future establishment of provenance trials. The area investigated within each stand var- species is based on regional provenance ied between 15 and 20 ha. A random sample of trials (Krahl-Urban, 1959; Kleinschmit, 120 acorns was taken from each bulked seed lot 1993). Allozyme variation studies have and used for further analysis by electrophoresis. only recently been started and have also Acorns were soaked in water for 24 h and ger- been limited to a regional scale (in Germa- minated on vermiculite in an incubator. When the ny, Müller-Starck and Ziehe, 1991; in radicle was 2-4 cm long, enzymes were extracted France, Zanetto, 1989; Kremer et al, from the radicle tissue by means of a 0.1 M Tris- HCl buffer, pH 8, with the addition of 0.007 M L- 1991).These have shown that sessile oak cysteine, 0.006 M ascorbate, 0.5% Tween-80, 4% exhibits high levels of within-stand gene di- polyvinylpyrrolidone, 0.5 M saccharose (Tobolski, versity compared to other forest species. 1978). Enzymes were separated from crude ho- However, differentiation among stands, mogenates by standard horizontal starch-gel within the frame of the population sample, electrophoresis (gel concentration 12%, w/v). The is extremely low. Similar results have been compositons of electrode and gel buffers are found in other oak species with wide distri- shown in table I. Buffer formulations for enzyme stains were adapted from Cheliak et al (1984), bution ranges (Quercus macrocarpa, Conkle et al (1982) and Vallejos (1983). Schnabel and Hamrick, 1990; Quercus Six enzymes were analysed for the population ilex, Lumaret and Michaud, 1991). survey. They corresponded to 6 encoding loci (ta- Allozymes studied in population surveys ble II). Mendelian inheritance of alleles was veri- usually correspond to enzymes involved in fied by means of segregation analyses in con- primary and secondary metabolism. The trolled crosses (unpublished data). Three enzymes are involved in primary metabolism, and objective of this study was to evaluate lev- the remaining 3 in secondary metabolism (re- els of within-population variation and ge- spectively, groupsI and II) (Bergmann, 1991). netic differentiation between populations Allelic frequencies were estimated within over the range of the species. Special at- each population; observed and expected hetero- tention has been given to the comparison zygosities within populations were calculated ac- of gene diversity statistics between the 2 cording to Brown and Weir (1983). Parameters classes of enzymes. of gene differentiation between populations (G ) st
calculated with Nei’s (1973, 1977) genetic were cus, the frequency of the most common al- diversity statistics. Confidence intervals of G st in the cases of the PGM, lele was > 0.9; were calculated by bootstrapping over popula- PGI and MR loci, it varied between 0.75 tions (500 bootstrap samples) (Efron, 1979). and 0.9; whereas for ACP and DIA, it equalled 0.6. Clearly the difference in fre- RESULTS quency profiles separated the 2 enzyme groups. The frequency profiles were con- sistent over all populations except for locus Frequency profiles ACP. For example, in each population, the most common allele of GOT showed a fre- Frequency profiles differed markedly quency > 0.9, ranging from 0.9 to 0.97. among the different loci. For the GOT lo- However, despite this consistency, the alle-
lic frequency differences between popula- heterozygosities compared to all other tions were significant. populations. Due to the large sample size population (120 seeds), standard er- per of heterozygosities were lower than rors Within-population genetic variation 0.01, indicating that the above-mentioned differences between western and eastern populations are significant. However, for Enzymes of group II exhibited higher hetero- enzymes of group II, the overall range of zygosities than enzymes of groupI be- differences among populations was lower cause of their different frequency profiles than in group I, and there was no apparent (table III). geographic trend of variation. There were important differences in lev- els of observed and expected heterozy- gosities among populations, particularly for Differentiation among populations enzymes of group I. In addition, there was a clear geographic pattern of variation of expected heterozigosity. Populations origi- Coefficients of gene differentiation (G ) st nating from the eastern part of the natural among populations were calculated for 2 range (12, 16, 17, 33, 34 and 36) exhibited different samples: 1) all populations, and lower levels of variation. In addition, popu- 2) central populations only (1, 3, 6, 12, 17, lations from the south-western part of the 32 and 36). The choice of central popula- range (41 and 43) showed similarly low tions was arbitrary. The main objective of
Differentiation increased significantly for thisanalysis was to separate the total sam- ple of populations into 2 extreme geo- group II enzymes when the sample of pop- graphic groups, in order to verify whether ulations increased from the central to the separation in space had resulted in genetic whole range of distribution (table IV). The differentiation. Other combinations of 6-9 highest allelic frequency differences were populations were created to form the cen- found for locus ACP. In most populations, ACP had only 2 major alleles, each with a tral population group, but always excluding peripheral populations of the natural range. frequencies close to 0.5. However, popula- G values were consistent over all the tions located at the edges of the distribu- st tion range (33, 35, 37 and 42) differed, combinations. Therefore, only the results corresponding to one combination are pre- with allele 1 having frequencies varying be- sented here. tween 0.15 and 0.40. On the whole range basis, G values Bootstrapping enabled us to obtain the st vary between 0.02 and 0.05, showing no distribution of the G values. For a given st significant difference between loci (table locus, there are striking differences in the IV). However, in the central part of the nat- overlap of the distribution of G values cor- st ural range, group II enzymes showed low- responding to the 2 samples of popula- er differentiation than group I enzymes. tions. The distributions overlap completely
for groupI enzymes, indicating no differ- sizes may be the cause of these differenc- in levels of genetic differentiation. In es. Sessile oak is known to have extremely ences contrast, there is only a reduced overlap irregular and heterogeneous seed crops in for group II enzymes. northeastern France, Germany and more eastern European countries. Whereas along the Loire river a good crop occurs every 3 years, in northeastern France, DISCUSSION AND CONCLUSION bumper crops are extremely scarce. As a result, the density of fruiting trees is re- diversity in sessile oak populations Gene duced in the eastern part of the range as clearly differs according to the class of al- compared to the western side. On the oth- lozymes studied. Enzymes involved in sec- er hand, southern populations exhibiting ondary metabolism exhibited higher within- low levels of genetic variation (41, 43) are population variation than enzymes in- located on the edges of the natural range, volved in primary metabolism. These dis- where sessile oaks occur only in isolated crepancies were due to differences in alle- stands. Some of these stands may stem lic frequency profiles rather than to the from a narrower genetic base, or even number of alleles. These observations founder effects. confirm previous results found for other Genetic differentiation among stands is species when both groups of enzymes extremely low (G values varied between st compared (Bergmann, 1991). were 2 and 5%, depending upon the locus). Re- We found a geographic pattern of varia- ports on genetic differentiation in other tion of heterozygosity values for groupI range-wide studies of oaks provided simi- enzymes. Eastern and most southern pop- lar conclusions (Schnabel and Hamrick, ulations exhibited lower levels of genetic 1990 for Q gambelii and Q macrocarpa; variation. Similar results have been ob- Lumaret and Michaud, 1991 for Q ilex). tained from a larger number of loci in a While life-history traits (gene flow and out- survey of exclusively French populations crossing) explain only part of the low popu- (Kremer et al, 1991).Populations from lation differentiation (Hamrick and Godt, northeastern France had lower heterozy- 1990), the effects of evolutionary history gosity values. Variations in population are largely unknown. Sessile oak has been
Éditions Camus A Les Chênes. (1934-1954) restricted to southern Europe since the last Paul-Lechevalier, Paris, 1314 pp glaciation. As a result, today’s stands may Cheliak WM, Morgan K, Dancik BP, Strobeck C, originate from several glacial refugia. The Yeh FCH (1984) Segregation of allozymes in multi-refugia hypothesis should result in megagametophytes of viable seed from a higher gene differentiation between widely natural population of Jack pine, Pinus bank- separated populations. Information from a siana Lamb. Theor Appl Genet 69, 145-151 larger set of loci is necessary to clarify Clayton JW, Tretiak DN (1972) Amine-citrate buf- post-glacial migration pathways. fers for pH control in starch-gel electrophore- sis. J Fish Res Board Can 29, 1169-1172 G values calculated in our study are st similar to those found in regional studies Conkle DT, Hodgkiss PD, Nunnally L, Hunter S (1982) Starch Gel Electrophoresis of Conifer on sessile oak (Kremer et al, 1991; Müller- Seeds: A Laboratory Manual. US Dept Agric Starck and Ziehe, 1991).However, our re- Exp Stat, Gen Tech Rep PSW 64 sults clearly showed that only group I en- Efron B (1979) Bootstrap methods: another look zymes maintained the level of differ- same at the jacknife. Ann Stat 7, 1-26 entiation, regardless of the origin of the Hamrick JL, Godt MJ (1990) Allozyme diversity sample populations: st values corre- G in plant species. In: Plant Population Genet- sponding to the whole range did not differ ics, Breeding and Genetic Resources (Brown from G values calculated only for popula- st AH, Clegg MT, Kahler AL, Weir BS, eds) Sin- tions in the central part of the range. Group auer Associates, Sunderland, MA, 23-42 II enzymes tended to have increased lev- Kleinschmit J (1993) Intraspecific variation of els of differentiation as the sampling range growth and adaptative traits in European oak species. Ann Sci For 50 (suppl 1), 166s-185s increased. Interestingly, these enzymes Krahl-Urban J (1959) Die Eichen. Paul also showed the highest differentiation be- Parey- Verlag, Hamburg, 288 pp tween closely related species (Q robur and Kremer A, Petit R, Zanetto A, Fougère V, Q petraea; Kremer et al, 1991).The differ- Ducousso A, Wagner D, Chauvin C (1991) Nu- ent levels of differentiation between the 2 clear and organelle gene diversity in Quercus enzyme groups may be related to their robur and Q petraea. In: Genetic Variation in sensitivities to evolutionary forces. For European Populations of Forest Trees (Müller- group I enzymes, differentiation may result Starck G, Ziehe M, eds) Sauerländer’s-Verlag, from a balance between genetic drift and Frankfurt-am-Main, 141-166 gene flow, whereas natural selection may Lumaret R, Michaud H (1991) Genetic variation act as an additional force for group II en- in holm oak populations. In: Genetic Variation in European Populations of Forest Trees zymes. (Müller-Starck G, Ziehe M, eds) Sauerländer’s Verlag, Frankfurt-am-Main, 167-172 Müller-Starck G, Ziehe M (1991) Genetic varia- REFERENCES tion in populations of Fagus sylvatica L, Quercus robur L, and Q petraea Liebl in Ger- many. In: Genetic Variation in European Pop- F (1991) Isozyme gene markers. In: Bergmann ulations of Forest Trees (Müller-Starck G, Genetic Variation in European Populations of Ziehe M, eds) JD Sauerländer’s-Verlag, Forest Trees (Müller-Starck G, Ziehe M, Frankfurt-am-Main, 125-140 eds). Sauerländers-Verlag, Frankfurt-am- Main, 67-78 Nei M (1973) Analysis of gene diversity in subdi- vided populations. Proc Natl Acad Sci USA Brown AHD, Weir BS (1983) Measuring genetic 12, 3321-3323 variability in plant populations. In: Isozymes in Plant Genetics and Breeding, Part A Nei M F statistics and analysis of gene (1977) (Tanksley SD, Orton TJ, eds) Elsevier Sci- diversity in subdivided populations. Ann Hum Genet 41, 225-233 ence Publ, Amsterdam, 219-239
Scandalios JG (1969) Genetic control of multi- University, IN, USA, ference. Purdue 456- ple molecular forms of enzymes in plants: a 468 review. Biochem Genet 3, 37-79 Vallejos CE (1983) Enzyme activity staining. In: Schnabel A, Hamrick JL (1990) Comparative Isozymes in Plant Genetics and Breeding, analysis of population genetic structure in Part A (Tanksley SD, Orton TJ, eds) Elsevier Quercus macrocarpa and Q gambelii (Faga- Science Publ, Amsterdam, 469-515 ceae). Syst Bot 15, 240-251 Zanetto A (1989) Polymorphisme enzymatique du Tobolski JJ (1978) Isozyme variation in several chêne sessile (Quercus petraea (Matt) Liebl) species of oaks. In: Proceedings of the en France. DEA thesis, Université de Pau et Central Hardwood Tree Improvement Con- des Pays de l’Adour, Pau, France, 42 p