Possible mechanisms of symbiontmediated plant adaptation

At present, the mechanisms whereby Regiella improves performance of host aphid specifically on white clover are totally unknown. One possible mechanism is that Regiella is

Ampicillin

Buchnera

Buchnera

Figure 6.7 Diagnostic PCR for confirming selective elimination of Regiella infection from pea aphid. Lanes 1-6, control aphid lines injected with distilled water; lanes 7-12, treated aphid lines injected with ampicillin at a dose of 1 pg/mg body weight . In a part of the treated lines (3/33 lines), Regiella infection disappeared in the offspring, whereas Buchnera infection was not affected . Complete elimination of Regiella infection was confirmed over 10 successive generations using diagnostic PCR . G0, treated generation; G1, offspring of G0; and so forth .

Figure 6.7 Diagnostic PCR for confirming selective elimination of Regiella infection from pea aphid. Lanes 1-6, control aphid lines injected with distilled water; lanes 7-12, treated aphid lines injected with ampicillin at a dose of 1 pg/mg body weight . In a part of the treated lines (3/33 lines), Regiella infection disappeared in the offspring, whereas Buchnera infection was not affected . Complete elimination of Regiella infection was confirmed over 10 successive generations using diagnostic PCR . G0, treated generation; G1, offspring of G0; and so forth .

Table 6.2 Artificial Transfer of Regiella from Strain TUt to Strain AIST by Injection of Hemolymph

Injected Lines Injected Generation Successive Generations

Table 6.2 Artificial Transfer of Regiella from Strain TUt to Strain AIST by Injection of Hemolymph

Injected Lines Injected Generation Successive Generations

5—6

7—8

9—10

11—12

13—14

15—

1c

2d

24e

(8—9)a

(10—11)

(12—13)

(14—15)

(16—17)

(18—)

AIST-TUt

0/4b

0/6

2/6

4/6

6/6

8/8

10/10

10/10

20/20

AIST-TUt 2

0/4

0/6

3/6

4/6

6/6

8/8

10/10

10/10

20/20

AIST-TUt 3

0/4

0/6

2/6

5/6

6/6

8/8

10/10

10/10

20/20

a Days after injection (days after birth) .

b Number of infected offspring/number of offspring examined.

c Established from a nymph deposited 12-13 days after injection of the injected generation. d Established from a newborn nymph of generation 1. e About 6 months after injection.

Source: From Tsuchida, T. , Koga, R. , Meng, X.Y., Matsumoto, T., and Fukatsu, T. (2005) . Microb. Ecol. 49: 126133 With permission a Days after injection (days after birth) .

b Number of infected offspring/number of offspring examined.

c Established from a nymph deposited 12-13 days after injection of the injected generation. d Established from a newborn nymph of generation 1. e About 6 months after injection.

Source: From Tsuchida, T. , Koga, R. , Meng, X.Y., Matsumoto, T., and Fukatsu, T. (2005) . Microb. Ecol. 49: 126133 With permission involved in the physiological adaptation of the host aphid to the chemical composition of plant phloem sap . It has been shown that amino acid composition in phloem sap differs among plant species (Ziegler, 1975; Weibull, 1990; Douglas, 1993; Sandstrom and Petters-son, 1994; Wilkinson and Douglas, 2003) . Experiments with artificial diet rearing systems have shown that dietary amino acid composition certainly affects the aphid performance (Srivastava and Auclair, 1983; Prosser and Douglas, 1992; Sandstrom, 1994; Karley et al ., on vetch on white clover on vetch on white clover

Figure 6.8 Performance of Regiella-infected and uninfected aphids on vetch and white clover. Top panels: naturally Regiella-infected strain TUtdw (filled squares), and Regiella-eliminated strain TUtamp (open diamonds) . Bottom panels: Regiella-eliminated strain TUtamp/TUtamp (open diamonds), and Regiella-reintroduced strain TUtamp/TUt (filled squares) . Dots and bars indicate means and SD. Asterisks indicate statistically significant differences (Mann-Whitney U test: *, p < 0 . 05; **, p < 0 . 01; ***, p < 0 . 001) . (From Tsuchida, T., Koga, R ., and Fukatsu, T. [2004] . Science 303: 1989. With permission .)

Figure 6.8 Performance of Regiella-infected and uninfected aphids on vetch and white clover. Top panels: naturally Regiella-infected strain TUtdw (filled squares), and Regiella-eliminated strain TUtamp (open diamonds) . Bottom panels: Regiella-eliminated strain TUtamp/TUtamp (open diamonds), and Regiella-reintroduced strain TUtamp/TUt (filled squares) . Dots and bars indicate means and SD. Asterisks indicate statistically significant differences (Mann-Whitney U test: *, p < 0 . 05; **, p < 0 . 01; ***, p < 0 . 001) . (From Tsuchida, T., Koga, R ., and Fukatsu, T. [2004] . Science 303: 1989. With permission .)

2002) . Moreover, it has been suggested that dietary amino acid composition and concentration affect density and phenotypic effects of endosymbionts (Wilkinson et al ., 2001, 2007; Chandler et al ., 2008). Hence, it appears plausible that the amino acid quality and quantity in the phloem sap are relevant to the influence of Regiella on aphid performance on different plant species Amino acid compositions in the phloem sap of white clover and vetch are unknown, but it is conceivable that Regiella might provide essential amino acids that Buchnera cannot sufficiently synthesize from the phloem sap of white clover. However, Douglas et al . (2006) conducted experiments using a range of artificial diets, in which amino acid compositions varied, and found no evidence that Regiella provides essential amino acids

Alternatively, plant allelochemicals might be possible determinants of aphid performance on the different plants White clover contains an array of bioactive secondary metabolites including cyanogenic glycosides (Williams, 1987), which were suggested to be effective against herbivores including aphids (Dritschilo et al , 1979) Regiella might be able to detoxify the plant allelochemicals, as Symbiotaphrina kochii does in the cigarette beetle (Dowd, 1991)

To address which of these and other hypotheses is justifiable, further experimental studies on the physiological contribution of Regiella to the host aphid are needed . It will be pivotal to analyze the phloem sap composition of white clover and vetch and investigate eg a

1200 r fts o

1000

1000

0 10 20 Days after birth

Figure 6.9 Cumulative number of offspring of four pea aphid clones on vetch (filled symbols) and white clover (open symbols) . All these aphid strains harbor Buchnera only The aphids were reared on each of the plants in groups of ten, respectively. The experiments were repeated twice on each plant for each clone, and an average of two experiments is indicated . Experimental condition: 16L8D, 20°C .

0 10 20 Days after birth

Figure 6.9 Cumulative number of offspring of four pea aphid clones on vetch (filled symbols) and white clover (open symbols) . All these aphid strains harbor Buchnera only The aphids were reared on each of the plants in groups of ten, respectively. The experiments were repeated twice on each plant for each clone, and an average of two experiments is indicated . Experimental condition: 16L8D, 20°C .

the nutritional physiology of Regiella-infected and Regiella-free aphids using chemically defined artificial diets .

0 0

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