Herbivory-induced changes in the small-RNA transcriptome and phytohormone signaling in Nicotiana attenuata

Abstract

Phytohormones mediate the perception of insect-specific signals and the elicitation of defenses during insect attack. Large-scale changes in a plant's transcriptome ensue, but how these changes are regulated remains unknown. Silencing of RNA-directed RNA polymerase 1 (RdR1) makes Nicotiana attenuata highly susceptible to insect herbivores, suggesting that defense elicitation is under the direct control of small-RNAs (smRNAs). Using 454-sequencing, we characterized N. attenuata's smRNA transcriptome before and after insect-specific elicitation in wild-type (WT) and RdR1-silenced (irRdR1) plants. We predicted the targets of N. attenuata smRNAs in the genes related to phytohormone signaling (jasmonic acid, JA-Ile, and ethylene) known to mediate resistance responses, and we measured the elicited dynamics of phytohormone biosynthetic transcripts and phytohormone levels in time-course experiments with field-and glasshouse-grown plants. RdR1 silencing severely altered the induced transcript accumulation of 8 of the 10 genes, reduced JA, and enhanced ethylene levels after elicitation. Adding JA completely restored the insect resistance of irRdR1 plants. irRdR1 plants had photosynthetic rates, growth, and reproductive output indistinguishable from that of WT plants, suggesting unaltered primary metabolism. We conclude that the susceptibility of irRdR1 plants to herbivores is due to altered phytohormone signaling and that smRNAs play a central role in coordinating the large-scale transcriptional changes that occur after herbivore attack. Given the diversity of smRNAs that are elicited after insect attack and the recent demonstration of the ability of ingested smRNAs to silence transcript accumulation in lepidopteran larvae midguts, the smRNA responses of plants may also function as direct defenses.454-sequencing ͉ herbivore resistance ͉ JA signaling ͉ phytohormone regulation

A Genetic Network for Systemic RNA Silencing in Plants

“…The amplification program for sRNA library. The reads were cropped to remove adapter sequences and were aligned to the 734 reference sequences using Bowtie2 (Langmead and Salzberg, 2012 (Rabyov et al, 2004), GFP 792 transgene (Haseloff et al, 1997), 736 DCL1, DCL2, DCL3, and DCL4 gene sequences (Nakasugi et al, 2013) and a set of 737 50 tobacco miRNAs identified in Nicotiana plants (Pandey et al, 2008;Fig. 5;Supplemental 738 Data Set S1).…”

The Mechanistic Underpinnings of anago1-Mediated, Environmentally Dependent, and Stochastic Phenotype

“…In addition to orchestrating proper responses to abiotic stress, miRNAs also are implicated in response to biotic factors such as defense against pathogens and herbivores (Pandey et al, 2008;Várallyay et al, 2010;Zhang et al, 2011;Bozorov et al, 2012). There is abundant evidence from expression studies (Navarro et al, 2006;Pandey et al, 2008;Bozorov et al, 2012) that links miRNA expression to disease resistance pathways.…”

“…There is abundant evidence from expression studies (Navarro et al, 2006;Pandey et al, 2008;Bozorov et al, 2012) that links miRNA expression to disease resistance pathways. For example, MIR393 is up-regulated in response to bacterial flg22, a potent trigger of innate immunity in plants (Nürnberger and Brunner, 2002).…”

The Road to RNA Silencing is Paved with Plant-Virus Interactions

“…Some of these RdRps are now known to be involved not only in RNA silencing, but also in transcriptional silencing of DNAs and the epigenetic control of gene expression (Chan et al, 2004;Lippman and Martienssen, 2004;Wassenegger, 2005). RdRps are also involved in innate resistance, including the salicylic acidmediated defense response (Gilliland et al, 2003;Xie et al, 2001;Yang et al, 2004) and the jasmonic acid-mediated defense response (Pandey and Baldwin, 2007;Pandey et al, 2008). Thus, the RdRps are key components of quite different defense pathways, providing defenses against viruses, bacteria, fungi and insects (Boller and Felix, 2009;Carr et al, 2010;Chisholm et al, 2006).…”