Coiling shoot (csh), a new mutation affecting shoot gravitropism

Gorel, F.L. and Berdnikov, V.A.             Inst. of Cytology and Genetics, Russian Academy of Sciences

                                                                                                                         Novosibirsk, Russia

      In 1997 we developed a pea line, Delta, that permitted the maintenance of a heterozygous segment of linkage group V between loci det and curl (Fig. 1) (1).  This construct is based on a sporophytic lethal tl^x, which is probably a small deletion of a chromosome fragment carrying the Tl gene.  As a result, recombination between loci r and tl is significantly suppressed.  For this reason, all round seeds of the line Delta have genotype R tl^x / r Tl.  Allelic composition of the Sca locus coding for a seed protein is easily determined by electrophoresis of proteins in a small quantity of cotyledon flour. Thus, to maintain this line, round seeds heterozygous for Sca should be picked out and the resulting plant self-pollinated. The presence of the det and curl markers is verified by sowing of wrinkled seeds. In the line Delta meiotic recombination is decreased about three times as compared to the standard map, for this reason the majority of seeds retain the flanking markers (1).

      The line Delta can be used to obtain recessive mutations in a chromosome segment between R and Sca.  These mutations can be identified by simply comparing phenotypes of plants grown from round and wrinkled seeds.  One hundred and fifty seeds of the line Delta were treated with 0.1% EMS and planted in a hydroponic bed.  Seed was collected from the 100 most fertile plants.  Two seeds from each of these plants were germinated and grown to maturity.  Round and wrinkled seeds from M₂ plants were sown in the field. In one family (E-65) seedlings from only the round seeds emerged, the seedlings from the wrinkled seeds often staying buried because shoots apparently had lost negative gravitropism (Fig.2).  The direction of growth of the shoot apex in the mutants seemed to be randomly determined and changed when the shoot tip contacts with any mechanical obstacle. While under ground, etiolated shoots grow by epicotyl extension.  However, once the shoots breaks through the soil surface, the plant starts growing upward, presumably responding by positive phototropism.  Hence, the traits of the adult plant can be registered.  We called this mutation affecting normal negative gravitropism of shoots coiling shoot (csh).

      The plants grown from round seeds of the E-65 family were crossed with the line DAG (Det, a, R, Tl, His1^f, SCA^s, Curl), isolated from the accession VIR-5538 (Daghestan).  Four F₁ seeds heterozygous for SCA produced plants hetero-zygous for His1, tl and r. Segregation of phenotypes in the F₂ is shown in Table 1.

 Table 1. Joint segregation data for the F₂ progeny of the cross E-65 (r, tl, csh, His1^s, SCA^f, curl) X DAG (R, Tl, Csh, His1^f, SCA^s, Curl).

¹ 'h' stands for heterozygotes. Total number of plants analyzed is 190.
² P<0.0001.
All dominant genes are in coupling phase.
All calculations were made with the program 'Cros' using the maximum likelyhood method.

Recombination relationships of the new locus are given in the following diagram.

      Thus, the new locus Csh is situated in linkage group V between tl and His1 loci at approximately equal distances.

      In higher plants, the shoots exhibit negative gravitropism, which is one of the most important phenomena in plant growth and development. In pea, the ageotropic mutation is known (2), which affects root growth and to a less extent decreases negative gravitropism of the shoot.  It has been mapped to linkage group IV (3). The new mutation csh does not effect gravitropism of the roots and together with age can be used to study one of the most important features of the plant.

Acknowledgement: This work was partly supported by the Russian State Program 'Russian Fund for Fundamental Research', grant No 99-04-49970.

1.   Berdnikov, V.A., Gorel, F.L., Bogdanova, V.S., Kosterin, O.E., Trusov, Y.A. and Rozov, S.M.  1999.  Genet. Res. 73: 93-109.

2.   Sch�ldeen, C. and Burstr�m, H.  1960.  Physiologia Plantarum 13: 831-838.

3.   Weeden, N.F., McBroom, M., Przyborowski, J. and Burger, P.  2000.  Pisum Genetics 32: 51-52.