Pisum Genetics Volume
27 1995 Research Reports pages 1-4
Further
data on the genes controlling anthocyanin pigmentation in the pea
Bogdanova, V.S., Trusov, Y.A. Institute
of Cytology and Genetics
and Kosterin, O.E.
The pattern of
anthocyanin colouration of various organs, other than the corolla, of the pea
plant is known to be controlled by a number of genes (1, 7). The gene D causes
a single or double anthocyanin ring or several spots at the base
of the stipules; the gene And determines irregular dots on the upper
surface of the leaflets and stipules; the gene Ans brings about a red
suffusion of the stem. Several symbolised genes control colouration of the pod:
the dominant alleles of genes Pur and
Pu together confer purple pods (3) and gene Astr causes the
purple stripes on the pod wall in some accessions of Pisum fulvum (4).
It was reported (6) that two recessive
genes rup and rups are responsible for a row of purple, roundish
spots on the pod wall corresponding
to the seeds forming inside, while two genes sru and srub control
the purple colouration of the upper seam of the pod; the same line, WL1293, was
specified as the type line for all
four genes rup, rups, sru and srub. No further data have been
reported on the inheritance of the
two latter characters and the reality of the four corresponding genes demands further thorough investigation. The genetic
control of other patterns, such as the variable anthocyanin colouration of the pedicel and of the red spots at the
leaflet bases, has not been investigated.
Identification of the
genotype of a plant by phenotypic manifestation of the above genes is difficult
due to an interaction of the genes and, in some cases, their probable identity
to each other.
Four of the genes
pertinent to anthocyanin distribution, namely, D, Pur, And, and Ans, are known to be located in the same region of the
genome (1, 7). Although the data available demand certain caution in
interpreting, one can infer the genes controlling the distribution of anthocyanin pigmentation form clusters on the linkage map.
We present here some
observations on the inheritance of the pod colouration, the axillary anthocyanin ring, and the spots at the leaflet bases. We suggest that
the funiculus colouration can aid in
identification of the genes Pur and Pu. In addition, we propose
that Astr and Pur may be the same gene
and that the spots at the leaflet bases may be another effect of the gene D.
We have analysed
segregation for the purple colouration of the pod in the cross WL-577 x VIR-5797. Line WL-577 has purple pods and is homozygous dominant for Pur
and Pu (1). Line VIR-5797 has green pods. In the same
cross we observed segregation for anthocyanin colouration of the funiculus.
This kind of colouration was also observed by Lamprecht (2) in plants with purple pods but detailed analysis of
inheritance of this character was not carried out.
Among 290 plants of
the F2 generation, we observed segregation for the colour of the pod
wall and the colour of the funiculus as shown in
Table 1 (sometimes the anthocyanin colouration of the funiculus was reduced
only to its very base, but yet was distinctly observable).
Table 1. Segregation for the colour of the pod wall and the colour of
the funiculus in the cross WL577 x VIR-5797.
|
|
Purple pod |
Green pod |
Total |
|
Coloured funiculus |
126 |
39 |
165 |
|
Colourless funiculus |
0 |
50 |
50 |
|
Not determined* |
38 |
37 |
75 |
|
Total |
164 |
126 |
290 |
* Funiculus colour was not detennined for 75 of
the F2 plants because they had not attained the relevant slage of development before the
experiment was terminated due to restrictions on time and space. Pod colour was
already apparent just after pod elongation
ceased while funiculus colour was not examined until the seeds had undergone further development.
Table
2. Segregation for the presence/absence of the anthocyanin ring in the leaf
axils and presence/absence of colour of
the funiculus in the F2 of cross WL-1081 x "Sprint-26".
|
|
Ring present |
Ring absent |
Total |
|
Coloured funiculus |
66 |
1 |
67 |
|
Colourless funiculus |
6 |
26 |
32 |
|
Total |
72 |
27 |
99 |
Chi-square (3:1) is 2.83 (P<0.05) for the
funiculus colour and 0.27 (P>0.6) for the ring. The joint segregation Chi-square is 69.5 (P<0.0001) and the recombination
fraction 6.84 ± 2.84%.
Table 3. Segregation for the presence/absence of the dots at the leaflet
bases and presence/absence of purple stripes on the pod wall in the F 2
of cross WL-1238 x F3 [VIR-6070 (
P.fulvum) x WL-1255]
|
|
Dots present |
Dots absent |
Total |
|
Stripes present |
52 |
8 |
60 |
|
Stripes absent |
6 |
20 |
26 |
|
Total |
58 |
28 |
86 |
Chi-square (3:1) is 2.62 (P>0.1) for the dots and 1.25 (P>0.2) for
the stripes. The joint segregation
Chi-square is 33.4 (P<0.0001) and the recombination fraction 16.0 ± 4.4%.
The observed ratio
of the number of purple-podded plants to that of green-podded plants (164:126) corresponds well to the 9:7 ratio (Chi-square = 0.01)
expected in the case of two complementary
dominant genes. Thus, we can confirm that in our case the purple colouration of the pod is determined by the
simultaneous presence of two dominant genes, as is assumed for the line WL-577.
At the same time, segregation for the anthocyanin colouration of the funiculus followed a monogenic mode of inheritance, the observed
ratio 165:50 corresponding well to 3:1
(Chi-square = 0.26). If we consider separately the classes with coloured and
colourless funiculus, we notice that in the former class segregation for the colouration of the pod is of a monogenic character, as the ratio 126
purple : 39 green is in a good accordance with
3:1 (Chi-square = 0.17). However, segregation for the pod colouration was not observed among plants with a colourless funiculus. Thus, not one
of the purple- podded plants had a colourless
funiculus, while the green-podded plants segregated for colouration of the funiculus in the proportion 39
coloured: 50 colourless, corresponding well to 3:4 ratio
(Chi-square = 0.03). The proportions of phenotypic classes: 126 purple pod,
coloured funiculus : 39 green pod, coloured
funiculus : 50 green pod, colourless funiculus are well described by the digenic ratio 9:3:4 (Chi-square
= 0.69).
The observed
segregation for the two characters allows us to suppose that one of genes of the
pair Pur and Pu determines anthocyanin colouration of the
funiculus, while addition of the other gene
extends this colouration to the entire pod.
In order to
elucidate which of the genes Pu and Pur is responsible for each
effect we tried to estimate genetic linkage between anthocyanin colouration of
the funiculus and other traits of the plant We
performed a cross WL-1081 x "Sprint-26"; the former line has a red
funiculus and markers D, wsp, n and i, while the latter line has
a colourless funiculus and markers d, Wsp, N and I. In addition, these lines also differed in allelic composition of
the histone H1 loci His(2-6) and
His7. An analysis of 99 plants in the F2 generation
(Table 2) showed significant linkage between
colourless funiculus and gene d, with a recombination fraction of
6.84±2.84% (estimated by the maximum likelihood method) and a
joint segregation Chi-square of 69.5 (P<0.0001).
Thus we conclude the gene determining anthocyanin colouration of the funiculus is Pur since this gene is known to be
linked to D (1).
Purple colouration of
the pod has rather a variable expression and the gene Pur is supposed to be highly mutable and to be associated
with a series of weaker alleles determining variation in the
extent of the coloured area of the pod surface (2). However, an alternative
explanation can be proposed for this variability - the existence of a series of
genes modifying expression of Pur, and Pu may be one of the
strongest of these modifiers.
Another character
associated with the distribution of anthocyanin colouration is the presence of anthocyanin dots at the base of leaflets.
The character was involved in the testcross (RT1 x WL-1238) x 6-14.
158 plants resulting from this testcross segregated for presence/absence
of the dots at the base of leaflets. At the same time, they also segregated for
presence/absence of the anthocyanin ring at
the bases of the stipules caused by alleles Dco and d, respectively. Since one of the parents, WL-1238 (as
well as the line 6-14 used for pollination of the F1, hybrids), was void of both dots and axillary ring,
these characters evidently came from
RT1 where they were not observable because of the repressed anthocyanin
production (this line carries allele
a). (Note that all the plants of the testcross progeny received the
allele A from line 6-14 and so did not segregate for anthocyanin
production). We found that the dots at the
leaflet bases were absolutely coupled with the anthocyanin ring caused by D
co: 82 plants had both dots and rings while 76 plants lacked both
characters; those numbers are in good accordance with a 1:1 ratio
(Chi-square = 0.23, P>0.6). Taking into account the full fertility of the F1
plants, suggesting that no noticeable chromosomal rearrangements were involved
in the cross, one can suppose that these two
evidently homologous characters are coded by two extremely closely
linked genes or, more probably, are manifestations of the same allele Dco
of the gene D.
We made another attempt at mapping the gene determining the dots at the
leaflet bases in the cross WL-1238 x F3
[VIR-6070 (P. fulvum) x
WL-1255]. The latter parent was represented by a single F3
plant originating from the mentioned cross. This F3 plant possessed red dots at the base of leaflets (but no axillary
anthocyanin ring), anthocyanin stripes on the pod surface, yellowish colouration of the flower
(evidently coming from P. fulvum
), as well as genes wlo and
p (evidently from WL-1255). The WL-1238 parent is void of anthocyanin colouration except for the flowers, lacks
yellowish colouration of the corolla, and has a number of recessive markers - r, tlw, gp,
le, wb, b and k. In addition, the parent plants differed in allelic composition of histone H1 loci His(2-6)
and His7. All descendants of the cross were fully fertile, thus indicating absence of
chromosomal rearrangements, although there occurred in the F2 a number of plants with the
"chlorotica" phenotype which eventually died.
An analysis of 86 F2
plants (Table 3) showed significant linkage (recombination fraction 16.0 ± 4.4%; joint seg. Chi-square = 33.4, P<0.0001) between ihe gene
determining red dots at the bases of
leaflets and the gene conditioning purple stripes on the pod (Astr). Both genes came from P. fulvum and, as discussed earlier, the former of them
might be the gene D represented in this
species by an allele which is expressed in such a way. The distance between the
gene determining the red dots at the bases of the leaflets and Astr is
quite similar to that between D and Pur, thus allowing us to
speculate that the Astr phenotype is a manifestation of Pur specific
to P. fulvum.
Thus, our data suggest that colouration of
the funiculus is the character which reliably indicates
the presence of the dominant allele of the gene Pur and hence, allows
the phenotypic classes Pur Pu and Pur pu to be
distinguished. In addition, our data indicate that the two traits purple
stripes on the pod (Astr) and
purple pods (Pur) may be
manifestations of the same gene. Likewise,
the two traits reds spots at the leaflet bases and anthocyanin ring in the leaf
axils (D ) may be
determined by the same gene.
Acknowledgments.
This work was partially supported by the Russian
National Programs "Frontiers in Genetics" and "Basic
Research Foundation".
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6.
Lamprecht, H. 1963. Agri Hort. Genet 21:149-158.
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