VIEW ARTICLE

Genetics

Soluble Proteins as Genetic Markers in Studies of Resistance and Phylogeny in Nicotiana. P. Ahl, Station d’Amélioration des Plantes, I.N.R.A., BV 1540, 21034 Dijon - Cedex, France; A. Cornu(2), and S. Gianinazzi(3). (2)(3)Station d’Amélioration des Plantes, I.N.R.A., BV 1540, 21034 Dijon - Cedex, France. Phytopathology 72:80-85. Accepted for publication 1 May 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-80.

New soluble proteins (b-proteins) appear in Nicotiana when resistance is induced either by a hypersensitive reaction to infection or by treatment with chemicals. Determination of their patterns in several species and cultivars has revealed both interspecific and interspecific variations. The b-proteins of Nicotiana sylvestris (R_f’s: b₀ = 0.88, b₁ = 0.83, b₃ = 0.56), Nicotiana tomentosiformis (R_f: b₂ = 0.66) and of 16 cultivars of Nicotiana tabacum (R_f’s: b₁ = 8.83, b₂ = 0.66, b₃ = 0.56 and, in five cultivars, b_1’ = 0.79) are charge isomers with a molecular weight of 15,700. Protein b₄ (R_f = 0.53), which is present in eight tobacco cultivars, has a molecular weight of 29,500. The determinants of these proteins are sexually transmitted and a monogenic inheritance has been demonstrated for one of them (b_1’). The hypothesis on the origin of present-day tobacco is strengthened by the observation that N. tabacum seems to have inherited b-proteins from both N. sylvestris (b₁ and b₃) and N. tomentosiformis (b₂). Resistance to TMV in N. tabacum comes from the introduction into this species of a resistance gene from Nicotiana glutinosa, the N gene. The b-protein found in this latter species, b_1” (R_f = 0.76; mol wt = 13,800) differs from tobacco b-proteins. However, since the N gene is required for b-protein elicitation in tobacco after TMV infection, it is suggested that this resistance gene may play a regulatory role on the structural gene(s) coding for the b-proteins. The use of b-proteins as genetic markers for studies on resistance and for phylogenetic investigations is proposed.