The Solanum lycopersicum RNaseLER is a class II enzyme of the RNase T2 family and shows preferential expression in guard cells

Ribonucleases (RNases) occur in different gene families, functioning in RNA processing and degradation. In this study, we report on cloning and characterization of RNaseLER, the first class II gene of the RNase T2 family in tomato (Solanum lycopersicum). The family also includes the class I members RNaseLE and RNaseLX, and the class III group of S-RNases acting in self incompatibility. The RNaseLER gene was cloned by polymerase chain reaction (PCR)-assisted methods. Structural analyses of RNaseLER and homologous genes revealed unique key features of class II RNase T2 genes. RNaseLER is a single copy gene in tomato and codes for a primary protein of 260 amino acids. Subcellular localization analyzed with a RNaseLER-eYFP fusion protein and co-localization experiments revealed an intracellular accumulation in the endoplasmic reticulum. Transgenic Nicotiana benthamiana plants carrying the uidA reporter gene under the control of a 900-bp RNaseLER promoter sequence express the reporter gene predominantly in guard cells and trichomes. This previously unknown spatial expression of a RNase T2 gene is consistent with ubiquitous detection of low RNaseLER transcript abundances in almost all parts of tomato plants. As revealed by quantitative real-time RT-PCR analysis treatments with abscisic acid, ethylene or other abiotic and biotic stress factors did not affect RNaseLER expression significantly. Unlike tomato class I genes, RNaseLER represents a constitutively expressed gene with a cell-specific role in stomata and trichomes and no involvement in stress responses.