Identification and Characterization of Stress-Responsive TAS3-Derived TasiRNAs in Melon

[EN] Small interfering RNAs (siRNA) are key regulators of gene expression that play essential roles in diverse biological processes. Trans-acting siRNAs (tasiRNAs) are a class of plant-endogenous siRNAs that lead the cleavage of nonidentical transcripts. TasiRNAs are usually involved in fine-tuning development. However, increasing evidence supports that tasiRNAs may be involved in stress response. Melon is a crop of great economic importance extensively cultivated in semiarid regions frequently exposed to changing environmental conditions that limit its productivity. However, knowledge of the precise role of siRNAs in general, and of tasiRNAs in particular, in regulating the response to adverse environmental conditions is limited. Here, we provide the first comprehensive analysis of computationally inferred melon-tasiRNAs responsive to two biotic (viroid-infection) and abiotic (cold treatment) stress conditions. We identify two TAS3-loci encoding to length (TAS3-L) and short (TAS3-S) transcripts. The TAS candidates predicted from small RNA-sequencing data were characterized according to their chromosome localization and expression pattern in response to stress. The functional activity of cmTAS genes was validated by transcript quantification and degradome assays of the tasiRNA precursors and their predicted targets. Finally, the functionality of a representative cmTAS3-derived tasiRNA (TAS3-S) was confirmed by transient assays showing the cleavage of ARF target transcripts. J.M. was the recipient of a predoctoral contract from the ACIF program (ACIF-2017-114) of the Conselleria d¿Educació, Investigació, Cultura i Esport Generalitat Valenciana. A.C. was the recipient of a postdoctoral contract from the Ramón y Cajal program (RYC-2017-21648) from the Ministerio de Ciencia, Innovación y Universidades (MCIU, Spain), Agencia Estatal de Investigación (AEI, Spain) and Fondo Europeo de Desarrollo Regional (FEDER, European Union). The Spanish Ministry of Economy and Competitiveness [grant numbers AGL2016-79825-R, BIO2014-61826-EXP to G.G.]; the Ministerio de Ciencia, Innovacion y Universidades (MCIU, Spain), Agencia Estatal de Investigacion (AEI, Spain) and Fondo Europeo de Desarrollo Regional (FEDER, European Union) [grant numbers BIO2017-83184-R to J.-A.D. and RTI2018-095118-A-100 to A.C.]. Cervera-Seco, L.; Marques, M.; Sanz-Carbonell, A.; Márquez-Molins, J.; Carbonell, A.; Daros Arnau, JA.; Gomez, GG. (2019). Identification and Characterization of Stress-Respon