microRNA160 dictates stage‐specific auxin and cytokinin sensitivities and directs soybean nodule development

Abstract

SUMMARYLegume nodules result from coordinated interactions between the plant and nitrogen-fixing rhizobia. The phytohormone cytokinin promotes nodule formation, and recent findings suggest that the phytohormone auxin inhibits nodule formation. Here we show that microRNA160 (miR160) is a key signaling element that determines the auxin/cytokinin balance during nodule development in soybean (Glycine max). miR160 appears to promote auxin activity by suppressing the levels of the ARF10/16/17 family of repressor ARF transcription factors. Using quantitative PCR assays and a fluorescence miRNA sensor, we show that miR160 levels are relatively low early during nodule formation and high in mature nodules. We had previously shown that ectopic expression of miR160 in soybean roots led to a severe reduction in nodule formation, coupled with enhanced sensitivity to auxin and reduced sensitivity to cytokinin. Here we show that exogenous cytokinin restores nodule formation in miR160 over-expressing roots. Therefore, low miR160 levels early during nodule development favor cytokinin activity required for nodule formation. Suppression of miR160 levels using a short tandem target mimic (STTM160) resulted in reduced sensitivity to auxin and enhanced sensitivity to cytokinin. In contrast to miR160 over-expressing roots, STTM160 roots had increased nodule formation, but nodule maturation was significantly delayed. Exogenous auxin partially restored proper nodule formation and maturation in STTM160 roots, suggesting that high miR160 activity later during nodule development favors auxin activity and promotes nodule maturation. Therefore, miR160 dictates developmental stage-specific sensitivities to auxin and cytokinin to direct proper nodule formation and maturation in soybean.

Class C ARFs evolved before the origin of land plants and antagonize differentiation and developmental transitions in Marchantia polymorpha

“…The class C ARF/MIR160 module in angiosperms regulates a range of processes including leaf margin complexity and lamina growth (Mallory et al ., ; Hendelman et al ., ; Ben‐Gera et al ., ), nodule formation in soybean roots (Turner et al ., ; Nizampatnam et al ., ), root meristem patterning (Wang et al ., ; Ding & Friml, ; Bennett et al ., ) floral determinacy (Liu et al ., ), ovary and fruit patterning, floral organ abscission (Damodharan et al ., ) and seed germination (Liu et al ., , ). Class C ARFs also promote the formation of shoot meristems in undifferentiated callus by directly repressing negative regulators of cytokinin signalling (Qiao et al ., ; Liu et al ., ).…”

Genome-wide identification and characterization of circular RNAs by high throughput sequencing in soybean

“…Some well-known miRNA families of MIR156 32, 33 , MIR172 34, 35 , MIR160 36 , MIR398 37, 38 , and MIR399 39 were predicted to be targeted by certain soybean circRNAs. Besides, we noticed that some miRNAs, such as miR482, miR1512, and miR1515 40 , which were related to soybean nitrogen fixation, were the putative targets of circRNAs in soybean.…”

The MicroRNA390/TAS3 Pathway Mediates Symbiotic Nodulation and Lateral Root Growth

“…target mimicry resulted in reduced sensitivity to auxin and increased nodulation (Nizampatnam et al, 2015). On the other hand, overexpression of miR160 in M. truncatula roots led to a reduction in nodule formation (BustosSanmamed et al, 2013), indicating that miR160 acts in both determinate and indeterminate nodules.…”