Pisum Genetics
2006—Volume 38
Research Papers
A gene for stem fasciation is localized on linkage group III
Sinjushin, A.A., Konovalov, F.A. and Gostimskii, S A.
Fasciation is one of the most widespread abnormalities of higher plant development. An understanding of the inheritance of the trait is very important, not only for theoretical purposes dealing with genetic control of meristem activity but also for practical use. Stem and fruit fasciation is used as an agriculturally valuable trait in selection of many species including pea (Pisum sativum L).
Genetics Dept. Biolog. Faculty of Moscow State Univ., Moscow, Russia
Fig. 1. Fasciated plant of “Shtambovy” mutant line (a) and scanning electronic microphotographs depicting stem apical meristems of “Shtambovy” mutant (b) and wild type plant (Nemchinovsky cultivar, c). Scale bar = 100µ.
The peculiarities of genetic control of fasciation in pea are still being discussed. There are few genes responsible for fasciation development; these genes form the
Table 1. Analysis of segregation at single loci in an F
2
population. A – homozygote as the first parental line (‘Shtambovy’), B – homozygote as the second parental line (WL1238), H – heterozygote, N – total number of plants analyzed.
fasciata family although little is known about their structure, protein products and even localization on the genetic map. The gene Fa (or Fa1 as was proposed by Swi§cicki and Gawlowska (8)) is localized in linkage group IV (4), Fa2 is in LG V (8) and Fas is supposed to be associated with LG III (1).
The fasciated mutant ‘Shtambovy’ was produced by induced chemical mutagenesis
Loci
A
H
B
N
X2 (P>0.05)
Egl1
27
58
29
114
0.11
PK4
25
32
25
82
3.95
Pepcn
18
35
23
76
1.13
Le
91
27
118
0.28
Fas
90
30
120
0.00
(ethylmethane sulfonate) from the cultivar ‘Nemchinovsky’ (6). This mutant exhibits strong
features of fasciation such as stem flattening, phyllotaxis abnormalities, clustering of axillary racemes on top of the stem, etc. (Fig. 1a). Such phenotype is connected with stem apical meristem enlargement which can be seen with usage of scanning electron microscopy. The apex of mutants becomes ridge-like (Fig. 1b) instead of hemispheric in wild-type plants (Fig. 1c) thus producing ribbon-like stem with multiple bundles and a striated surface. The morphology, anatomy and growth characteristics of fasciated plants compared with normal ones have been previously described (7).
The fasciation in a new mutant line is caused by a recessive mutation in a single gene (see Table 1).
Allelism tests revealed that the gene responsible for fasciation in ‘Shtambovy’ is not allelic to gene Fa from JI 5 (‘Mummy Pea’): all F1 plants from cross ‘Shtambovy’ x JI 5 were non-fasciated.
In order to determine the possible relationship between ‘Shtambovy’ mutation and
genes Fas and Fa2, an effort was made to localize the new fasciata locus on the pea linkage map. The F1 and F2 progeny of a cross ‘Shtambovy’ x WL
Fig. 2. Region of LG III containing gene Fas. Top numbers are genetic distances (cM), bottom numbers (in italics) are meanings of LOD score.
19
Pisum Genetics
2006—Volume 38
Research Papers
1238 were planted in the field. All F1 hybrids were monomorphic and exhibited a non-
Table 2. Segregations and joint chi-square values for the selected loci in F .
2
A – homozygote as the first parental line (‘Shtambovy’), B – homozygote as the second parental line (WL1238), H – heterozygote, C – dominant phenotype like in the second parental line, N – total number of plants analyzed.
Classes in segregation
Loci
CH CA
CB
AH AA
AB
N
Joint x2
Fas-Le
70
19
21
7
117
000.71
Fas-Egl1
44 10
24
9 14
0
101
067.14
Fas-Pepcn
28 5
17
5 8
0
063
038.36
Fas-PK4
23 8
17
7 16
3
074
122.81
fasciated phenotype. In the second filial generation the genetic analysis was performed involving the trait of interest and morphological markers
carried by parental lines. According to some
previous data (not shown) the gene of interest appeared to be associated with linkage group III. In order to check this hypothesis PCR-based CAPS markers (Cleaved Amplified Polymorphic Sequences) distributed across LG III were tested for linkage with the gene of interest. Primer sequences and reaction conditions were as described earlier (2, 3). The polymorphism was revealed by digestion of PCR products with restriction endonucleases Tru9I (for PK4), RsaI (for Pepcn) and AluI (for Egl1). F2 segregation data was processed using the program Mapmaker/EXP 3.0 (5). The logarithm of odds (LOD) threshold for the linkage estimation was set at 3.0; the recombination frequencies were converted to map distances in cM using the Kosambi mapping function. The chi-square values for all marker pairs are presented in Table 2.
We found significant linkage between the gene responsible for fasciata phenotype in ‘Shtambovy’ and CAPS markers from the bottom part of linkage group III. According to results the map of region containing this gene was constructed with morphological marker Le included (although the latter shows no linkage with fasciata gene in this cross).
As Fas is the only known fasciata gene associated with LG III, we propose that the gene causing fasciation in the ‘Shtambovy’ mutant is identical to Fas. More investigations on this point are needed including additional allelism tests. Regardless of the outcome of these tests, the new mutation can be used as an additional morphological marker in LG III and may provide new information concerning genetic control of stem development in pea.
Acknowledgement: The authors would like to express their gratitude to Prof. Noel Ellis and Dr. Mike Ambrose (John Innes Centre) for kindly providing them with the seeds of JI 5. The work was supported by Russian Foundation for Basic Research.
1.    Blixt, S. 1976. Agri Hort. Genet. 34: 83-87.
2.   Brauner S., Murphy, R.L., Walling, J.G., Przyborowski, J. and Weeden, N.F. 2002. J. Amer. Soc. Hort. Sci. 127: 612-622.
3.    Konovalov, F.A., Toshchakova, E.A. and Gostimsky, S.A. 2005. Cell. Mol. Biol. Lett. 10: 163-172.
4.   Lamprecht, H. 1952. Agri Hort. Genet. 10: 158-167.
5.    Lander, E.S., Green, P., Abrahamson, J., Barlow, A., Daly, M.J., Lincoln, S.E. and Newburg, L. 1987. Genomics 1: 174-181.
6.    Rehmatulla A., Gostimskii S.A. 1976. Biologicheskie nauki. 5: 107-112. In Russian.
7.    Sinjushin A.A., Gostimsky S.A. 2006. Russ. J. Dev. Biol. 37. In press.
8.    Swiecicki, W.K. and Gawlowska, M. 2004. Pisum Genetics 36: 22-23.
20