Rojas H. J. author Caspani C. author Escobar E. G. author Quiroga R. author Goldraij A. author text journal article 2018 In plants, class III T2 RNases involves two groups of structurally similar proteins, but with different biological functions: S-RNases and non-S-RNases. S-RNases have been involved in self-incompatibility whereas non-S-RNases have been implicated in stress responses. Here we report a novel class III RNase termed NaPi/S_x-RNase, which works both in self-incompatibility and in response to phosphate deficiency. The NaPi/S_x-RNase gene was identified in roots of Nicotiana alata grown in the absence of inorganic phosphate. Phylogenetic analysis showed that NaPi/S_x-RNase was included within the class III RNase T2 group. The NaPi/S_x-RNase was expressed in styles and its temporal expression increased in parallel to stylar development, with a slight decrease after anthesis. Progeny analysis showed that NaPi/S_x-RNase and S₁₀₇-RNase, a functional allele of the self-incompatibility system, segregated in a 1:1 ratio. The progeny segregation of a semicompatible cross, in which NaPi/S_x-RNase was shared by the two parents, exhibited a pattern consistent with a functional S-RNase allele. Considering genetic segregation, primary structure, and physiological role, the NaPi/S_x-RNase may be either an S-RNase with diversified functions or a non-S-RNase linked to the S-locus. To our knowledge, this is the first evidence for a specific function of the S-locus other than the self-incompatibility reaction. These results support the hypothesis that the self-incompatibility and stress responses may have evolved from a common origin. ribonuclease; self-incompatibility; S-locus; stress responses 10.1007/s10535-018-0783-6 https://bp.ueb.cas.cz/artkey/bpl-201802-0007.php https://bp.ueb.cas.cz/artkey/bpl-201802-0007.php continuing 62 2 261 268 2018 periodical academic journal