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. 2022 Jul 18;22:351. doi: 10.1186/s12870-022-03723-5

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© The Author(s) 2022

Open AccessThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.

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Fig. 3 — Model depicting the possible roles of miRNAs and phased secondary siRNAs (phasiRNA) in the regulation of R-genes. A Under normal conditions, when the host plant is not challenged, constitutive and unregulated expression of R-genes results in high fitness costs; B In the direct targeting pathway of R-genes by miRNA, the MIR loci produce miRNA transcripts that are processed to mature miRNAs. Subsequently, mature miRNA is complexed with AGO1/7 and directly binds to R-gene transcript followed by cleavage, resulting in basal resistance response and concomitant effects on fitness cost (box with dashed line). In the indirect targeting pathway of R-genes by miRNAs, the mature miRNA is produced from MIR loci and interacts with AGO1. The AGO1-miRNA complex binds to PHAS transcripts produced from the coding region of PHAS loci and cleaves the PHAS transcripts in a sequence-specific manner. SGS3 and RDR6 convert the single-stranded RNA to long double-stranded RNA which is processed by DCL4 to phased siRNA (phasiRNA). AGO1/7-phasiRNA complex cleaves R- gene transcripts and maintain the basal level of R-gene expression to achieve optimized and well-balanced resource usage for defense and maintenance of plant fitness by robust growth and development. R genes-resistance genes; AGO1-ARGONAUTE 1; SGS3-SUPPRESSOR OF GENE SILENCING 3; RDR6- RNA-DEPENDENT RNA POLYMERASE 6; DCL4- DICER-LIKE 4