Mapping of gene Inci, accompanied by new translocation, on linkage group III

 

Smirnova, O.G.                                                    Inst. of Cytology and Gen., Russian Acad. of Sci.,

                                                                                                                       Novosibirsk, Russia

 

      The line WIR2521 (Pisum sativum ssp. syriacum) has deeply incised leaflets produced by a dominant allele at the locus Inci. Linkage between Inci and b (pink wing petals) of linkage group III have been reported (2, 3). I.C. Murfet and T.H.N. Ellis have placed M, st, b, Np, le on the same linkage group (1). To more precisely map Inci, the line WL1238 was crossed with line WIR2521. Line WL1238 possesses a normal karyotype and produces fertile pollen. The karyotype of WIR2521 has not been determined, but its pollen is completely fertile. The F1 plants exhibited semi-sterile pollen (Fig.1A). Cytogenetic analysis was done to investigate the cause of the sterile pollen. There are 7 bivalents in meiotic metaphase I of pollen mother cells of the line WL1238. In metaphase I of F1 hybrids of the cross WL1238XWIR2521 one can see 5 bivalents and 1 quadrivalent instead of 7 bivalents (Fig.1 B, C). These results suggest that a transloction in the line WIR2521 may be responsible for semisterility of F1 hybrids.

          

A                                 B                                 C

Fig.1. Acetocarmine staining of mature pollen (A) and metaphase I of pollen mother cells (B, C). A sterile and fertile pollen of F1 hybrid WL1238xWIR2521; B seven bivalents at metaphase I in PMC of line WL1238; C five bivalents and one quadrivalent at metaphase I in PMC of F1 hybrid WL1238xWIR2521.

 

      Lines WL1238 (m, b, tr, inci, np, le) and WIR2521 (M, B, Tr, Inci, Np, Le) were used to make the testcrosses WL1238x(WL1238xWIR2521) and (WL1238xWIR2521)xWL1238. Line WL1238 was used as a female parent to avoid nuclear-cytoplasmic conflict. Such complications are observed when line WIR2521 is used as female parent (unpublished data). All markers were in coupling phase and segregated in accordance with a 1:1 ratio (Table 1). Segregation ratios obtained for Inci, also confirmed its monogenic nature. Dominant symbol Tr was used for designation of semisterile plants carrying the translocation. Accordingly, fertile plants without translocation were marked by recessive symbol tr. 

 

One hundred-fifty hybrid plants of two testcrosses were examined. One plant of the cross (WL1238 x WIR2521) x WL1238 and four plants of the cross WL1238 x (WL1238 x WIR2521) showed recombination between the loci b, Tr and Inci (Table 2). The data generate the following locus order:  

                       B Tr Inci

Thus the break point of the translocation (Tr) was mapped between B and Inci.

The plants number 15, 17 and 22 have m, B, inci/m, b, inci genotype. They are the result of double crossing-over between the loci M and Inci. These plants were taken into account for more precise determination of the distance between the genes M and Inci (Table 3). 

      Both crosses gave nearly the same results. The linkage map shown in Fig. 2 is based only on results of the testcross WL1238 x (WL1238 x WIR2521).

      The results can be presented as the follow segment for linkage group III:

 

Fig 2. Linkage map based on the data presented in Table 3.

 

      To determine the second chromosome involved in the translocation linkage of Inci with markers d, wb, tl, r, k, gp, and i was studied. For all comparisons low c2 values were obtained, indicating that the second chromosome involved was not that associated with linkage groups I (i, d), linkage group V (tl, r, pg).

      A new translocation of pea was described. A break point of a translocation is located between the genes b and Inci. Dominant gene Inci is tightly linked to the break point (nearly 1%). The translocation involves linkage group III and an unidentified chromosome. The translocation suppressed gene recombination inside of the region M b Np le. Dominant gene Inci is convenient marker for genetic studying of the region b Np.

 

1.   Murfet, I.C. and Ellis, T.H.N.  1998.  Pisum Genetics 30: 12-14.

2.   Swiecicki, W.K.  1990.  Pisum Newslett. 22: 64-65.