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Plant J. 1998 Dec;16(5):591-9.

A relic S-RNase is expressed in the styles of self-compatible Nicotiana sylvestris.

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Plant Cell Biology Research Centre, School of Botany, University of Melbourne, Parkville, Victoria, Australia.


We surveyed ribonuclease activity in the styles of Nicotiana spp. and found little or no activity in self-compatible species and in a self-compatible accession of a self-incompatible species. All self-incompatible species had high levels of ribonuclease activity in their style. Interestingly, one self-compatible species, N. sylvestris, had a level of stylar ribonuclease activity comparable to that of some self-incompatible Nicotiana species. A ribonuclease with biochemical properties similar to those of the self-incompatibility (S-)RNases of N. alata was purified from N. sylvestris styles. The N-terminal sequence of this protein was used to confirm the identity of a cDNA corresponding to the stylar RNase. The amino acid sequence deduced from the cDNA was related to those of the S-RNases and included the five conserved regions characteristic of these proteins. It appears that the N. sylvestris RNase may have evolved from the S-RNases and is an example of a 'relic S-RNase'. A number of features distinguish the N. sylvestris RNase from the S-RNases, and the role these may have played in the presumed loss of the self-incompatibility response during the evolution of this species are discussed.

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