Soluble Proteins as Genetic Markers in Studies of Resistance and Phylogeny inNicotiana

Publisher Website
Google Scholar
Abstract
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 intraspecific variations. The b-proteins of N. sylvestris (Rf: b0 = 0.88, b1 = 0.83, b3 = 0.56), N. tomentosiformis (Rf: b2 = 0.66) and of 16 cultivars of N. tabacum (Rf: b1 = 0.83, b2 = 0.66, b3 = 0.56 and, in 5 cultivars, b1'' = 0.79) are charge isomers with a MW of 15,700. Protein b4 (Rf = 0.53), which is present in 8 tobacco cultivars, has a MW of 29,500. The determinants of these proteins are sexually transmitted and a monogenic inheritance was demonstrated for 1 of them (b1''). 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 [tobacco mosaic virus] in N. tabacum comes from the introduction into this species of a resistance gene from N. glutinosa, the N gene. The b-protein found in this latter species, b1" (Rf = 0.76; MW = 13,800) differs from tobacco b-proteins. However, since the N gene is required for b-protin elicitation in tobacco after TMV infection, then 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.