biologia plantarum

Biologia plantarum 62:261-268, 2018 | DOI: 10.1007/s10535-018-0783-6

NaPi/S_X-RNase segregates as a functional S-RNase and is induced under phosphate deficiency in Nicotiana alata

H. J. Rojas¹, C. Caspani², E. G. Escobar², R. Quiroga³, A. Goldraij^2,*

¹ Instituto Universitario de Ciencias de la Salud, Facultad de Medicina, La Rioja, Argentina

² Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Córdoba, Argentina

³ Departamento de Química Teórica y Computacional, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Córdoba, Argentina

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.

Keywords: ribonuclease; self-incompatibility; S-locus; stress responses

Subjects: S-ribonuclease; self-incompatibility; phosphate deficiency; phylogenetic analysis; amino acid sequences; gene expression

Received: April 6, 2017; Revised: August 22, 2017; Accepted: August 24, 2017; Published: June 1, 2018  Show citation