Pisum Genetics Volume 27 1995 Research Reports pages 23-25

Chromosomes 2 and 6 are involved in the Twt-translocation

Temnykh, S.V., Gorel', F.L., Institute of Cytology and Genetics

and Berdnikov, V.A. Novosibirsk 630090, Russia

Weeden, N.F. Department of Horticultural Sciences

NYSAES/Cornell University, Geneva NY 14456, USA

A new translocation closely associated with the dominant mutation Twt (twisted tendrils) has recently been described (2). Gene Twt was mapped 8 cM from a (anthocyanin inhibition) in the direction of lf (lower flowering node). Trisomic analysis confirmed that the interchange chromosome includes the segment His(2-6) a Twt of linkage group IA (2). This linkage group is believed to belong to chromosome 6 (4, 5), making chromosome 6 a component of the Twt-translocation. Below we present cytogenetic data that identify chromosome 2 as the other chromosome involved in this translocation.

The Twt-line was crossed with known translocation lines from Lamm's tester set (5). Results of cytological analysis of the F1 hybrids are given in Table 1.

Table 1. Chromosome pairing in F1 hybrids between the Twt line and tester interchange lines.

 

Cross No.

Parental Lines

Chromosomes of tester line involved in translocation*

Chromosome configuration at metaphase I of meiosis

No. of bivalents

No. of
rings of 4

No. of
rings of 6

1

Twt x L84

3, 6

4

0

1

2

Twt x L83

3, 5

3

2

0

3

Twt x L21

3, 4

3

2

0

4

Twt x LI 14

1, 2

4

0

1

5

Twt x L108

2, 7

4

0

1

*Structural types of the tester interchange lines are given according to Lamm (5) and linkage groups are denoted in agreement with the version of the pea genetic map published in Vol. 25 of Pisum Genetics (8).

Results from the first three crosses confirm the involvement of chromosome 6 in the Twt-translocation (cross 1; Fig. 1 left) and exclude chromosomes 3, 4 and 5 as candidates for the other member of the interchange (crosses 2 and 3). The presence of one ring of six and four bivalents in both crosses 4 and 5 (Fig. 1 centre and right) suggests that chromosome 2 is the other chromosome involved in the Twt-translocation. The structural type of the Twt-translocation is thus postulated to be T(2,6).

In an attempt to confirm this conclusion we crossed the Twt-line with lines carrying markers of linkage group VI, the linkage group currently assigned to chromosome 2. However, joint segregation analysis (Table 2) gave no significant linkage between Twt and group VI markers Pl, Prx-3 and Acp-4, and only a weak linkage between Twt and wlo . The lack of linkage with these standard markers suggests that either the markers chosen do not cover the entire chromosome or that the wrong linkage group has been assigned to chromosome 2.

Table 2. Joint segregation data for Twt and markers of the linkage groups IA, IB and VI and the breakpoint of the translocation Twt.

Gene pair

Number of progeny with designated phenotype.1

c2

Recomb. frac.
S.E.

A/B

A/h

A/b

h/B

h/h

h/b

a/B

a/h

a/b

a) JI 73 (A, twt, His7F, d, IdhF) x Twt (a, Tw, His7S, Dco, IdhS)

a-Twt

2

45

22

-

-

-

21

5

0

63.1****

7 3

d-Twt

6

42

6

-

-

-

0

3

16

35.8****

11 4

His7 - Twt

18

3

0

2

35

6

0

4

11

80.1****

10 3

Idh - Twt

18

5

1

5

41

6

0

6

15

77.9****

13 3

a - His7

15

36

5

-

-

-

0

6

14

30.5****

14 4

a - Idh

20

42

8

-

-

-

0

9

16

29.3****

18 4

d - His7

7

30

6

-

-

-

0

6

9

13.2**

21 6

d - Idh

9

41

4

-

-

-

0

3

16

41.9****

9 3

His7 - Idh

9

6

2

4

32

4

0

6

15

47 3****

17 3

b) Twt (and, Twt. Acp-4S. Prx-3F) x Fast (And, twt, Acp-4F, Prx-3S)

And - Twt

5

66

27

-

-

-

20

5

1

66.0****

10 3

Acp-4 - Twt

5

17

3

29

26

16

3

12

13

18.0**

42 4

Prx-3 - Twt

4

12

9

20

31

20

9

15

4

4.4

58 4

And - Acp-4

30

38

30

-

-

-

2

17

7

7.5*

45 5

Prx-3 - Acp-4

6

18

12

22

29

12

10

16

9

4.7

55 4

c) Twt (Twt, Dco, Wlo) x NGB1514 (twt, d, wlo)

Twt - d

296

-

35

-

-

-

38

-

88

163****

17 4

Twt - wlo

214

-

35

-

-

-

72

-

26

7.6**

41 4

d - wlo

218

-

30

-

-

-

68

-

31

18.0****

36 5

d) Twt (Twt, pl) x K-3953 (twt, Pl)

Twt - Pl

105

-

31

-

-

-

13

-

5

0.2

45 6

1A,a=first gene; B,b=second gene; h=heterozygous. Where both genes are dominant, the capital letter stands for the dominant allele. Where the second gene is codominant, a capital A stands for the dominant allele of the first gene and capital B for an allele of the second gene which is in coupling with A. Where both genes are codominant, a capital letter stands for an allele of the first parent. *, **, **** P<0.05, 0.01 and 0.0001, respectively. Data were analysed using the CROS program developed by S.M. Rozov.

In contrast to the lack of linkage with group VI markers, Twt displayed clear linkage with genes on linkage group IB (d, and, Idh) (Table 2). Although a and d were placed on the same linkage group on the classical pea map, recent evidence (3, 6) indicates that the two genes are not on the same chromosome. Paruvangada et al. (6) found linkage of gene Enod1 with both a on group IA and Fum on group II and they suggest groups IA and II should be joined. They found no evidence of linkage between Enod2 and group IB markers. Likewise, in an earlier report, Kosterin (3) failed to show linkage not only between d and lf but also between d and the more distally situated group IA loci His7 and blb. Twt maps in the vicinity of lf and would not be expected to show linkage with d. However, our data indicate a recombination value of 10 to


Fig. 1. Chromosomal configurations at the first metaphase of meiosis in pollen mother cells of F1 hybrids: Left) Twt x L-84; Centre) Twt x L-l14; Right) Twt x L-108. Acetocarmine staining.

15% for d and Twt. This apparent contradiction may be explained if 1) the translocation strongly reduces the recombination in the lower part of linkage group I or 2) d belongs to the other linkage group involved in the translocation. The former hypothesis is weakened by our finding that the map distance between His7 and Twt is comparable to the distance between these loci in the absence of the translocation (1). Moreover, based on the data from cross JI 73 x Twt, Twt maps equally well between a and His7 and between His7 and d, indicating pseudo-linkage of the two regions and supporting the latter hypothesis. We also find a weak linkage observed between d and wlo (Table 2), suggesting that d may be part of linkage group VI, the linkage group conventionally assigned to chromosome 2 (7).

However, we do not have compelling evidence for combining linkage group IB with any of the other linkage groups in pea. Our results only demonstrate that translocation Twt involves chromosomes 2 and 6, that linkage group IA represents one of the chromosomes (presumably chromosome 6), and that linkage group IB displays linkage with Twt and what appears to be pseudo-linkage with linkage group IA in crosses involving the Twt translocation.

1.                       Berdnikov, V.A., Gorel, F.L., Temnykh, S.V. 1994. Pisum Genet. 26: 9-10.

2.           Gorel', F.L., Temnykh, S.V., Lebedeva, I.P. and Berdnikov, V.A. 1992. Pisum
Genet. 24: 48-51.

3.           Kosterin, O.E. 1993. Pisum Genet. 25: 23-26.

4.           Lamm, R. 1986. PNL 18: 34-36.

5.           Lamm, R. 1987. PNL 19:20-23.

6.           Paruvangada, V.G., Weeden, N.F., Cargnoni, T., Yu, J., Gorel', F., Frew, T.,
Timmerman-Vaughan, G.M. and McCallum, J. 1995. Pisum Genet. 27:12-13.

7.       Temnykh, S.V. and Weeden, N.F. 1993. Pisum Genet. 25:1-3.

8.         Weeden, N.F., Swiecicki, W.K., Ambrose, M. and Timmerman, G.M. 1993. Pisum
Genet. 25:4 and cover.