A new allele at the Tl locus

Pisum Genetics

2006—Volume 38

Research Papers

A new allele at the Tl locus — tl ^na

Rozov, S.M.

Inst. of Cytol. and Genet. Siberian Branch of Russ. Acad. of Sci., Novosibirsk, Russia

A mutant line SGE-0812 with a clavicula (1, 2) (tendrilless) phenotype was isolated from the M₂ progeny of EMS-treated pea line SGE. In addition to the classical acacia-like leaf appearance, line SGE-0812 carries some other striking features. The whole plant of SGE-0812 is one-half to one-third the size of the SGE parental line. All parts and organs of plant are diminished proportionally. We denote this phenotype as nana. In addition, the SGE-0812 line has a strong ramosus tendency, forming lateral branches of different length at almost every node (figs. 1 and 2). It should be noted that the plants of the parental line SGE have only the main stem and very rarely form short lateral branches.

Fig. 1. SGE-0812 mutant line. This plant has two well developed lateral branches and many short lateral branches, while the parental SGE line usually forms only a single main stem.

Fig. 2. Leaf of the SGE-0812 mutant (a) and the parental line SGE (b). Arrow indicates a lateral branch typical of the mutant line but rarely observed in the SGE parent.

Allelism test in the cross of SGE-0812 with the tester line WL1238 carrying the clavicula gene tl^w revealed that all F₁ progeny had an obvious tl (clavicula) phenotype. Thus, the SGE-0812 mutant evidently carries a new allele of the well-known tl gene. There remained the question whether the other phenotypic features of SGE-0812, such as size reduction (nana) and abundant branching (ramosus) result from an activity of the new tl allele or are independent mutation events. To clarify this uncertainty, I crossed the SGE-0812 line with the parental SGE line. In this cross all F₁ plants were of normal length, typical of the SGE line. The hybrid plants

Pisum Genetics

2006—Volume 38

Research Papers

also lacked any additional lateral branches but did show flattened tendrils, characteristic of Tl/tl heterozygotes. Only three phenotypic classes could be distinguished in the F₂ progeny of this cross, and their segregation ratio is given in Table 1.

Table 1. Phenotypic segregation in an F progeny from the cross between lines SGE-0812 and its parent

(SGE)

Tl /Tl, no nana, Tl / tl^w (flat tendrils),

Phenotype no ramosus no nana, no ramosus tl^w/tl^na, nana, ramosus

SGE-0812 X SGE 67 135 59 ___________________________________________________________________________________
c² for 1:2:1 = 0.8008, 0.3 < P < 0.4

The results from the segregation of phenotypes in the F₂ indicate that both the nana and ramosus features co-segregate with the clavicula type. Thus, it is highly probable that the new allele of the Tl locus (designated tl^na) affects not only the leaf structure, but the constitution of the entire plant. Tl has usually been considered a homeotic gene, active primarily in the development of leaf structures (3, 4). My results indicate that Tl can affect a broader range of organogenic processes.

Acknowledgement: The author is grateful to Vera S. Bogdanova for her discussion of this work and support in preparing the publication.

1. Blixt, S. 1972. Agri Hort. Genet. 30: 1–293.

2. Pisum Genetics Association Gene List. Pgene. http://www.jic.ac.uk/GERMPLAS/pisum/Zgc4g.htm

3. Gourlay, C.W., Hofer, J.M. and Ellis, T.H.N. 2000. Plant Cell 12: 1279–1294.

4. Yaxley, J.L., Jablonsky, W. and Reid, J.B. 2001. Ann. Bot. 88: 225–234.