miR393 and miR164 influence indeterminate but not determinate nodule development

Abstract

The roles of auxin in the regulation of symbiotic legume nodule formation are unclear. We recently showed that enhanced sensitivity to auxin resulting from overexpression of miR160 inhibits determinate nodule formation in soybean. We examined the roles of miR393 and miR164 in soybean (that forms determinate nodules) and Medicago truncatula (that forms indeterminate nodules). Our results together with previous studies suggest that indeterminate nodule formation requires a higher, but narrow window of auxin sensitivity and that miR164 regulation is not crucial for determinate nodule formation.

MicroRNA167-Directed Regulation of the Auxin Response Factors GmARF8a and GmARF8b Is Required for Soybean Nodulation and Lateral Root Development

“…The findings reported here shed light on the role of a critical miRNA in plant development and highlight its manipulation of auxin signaling to regulate nodule organogenesis and root system architecture. Clearly, our findings are not consistent with the previous research on the minor role of auxin signaling in determinant nodule development (Mao et al, 2013). A possible explanation for this contradictory result of auxin effects on determinant nodule development is that the particular miR393 family member used in the previous study may not be the one that plays a critical role in the development of determinant nodules.…”

“…This suggests that minimal or reduced auxin sensitivity of soybean root cells is required for determinate nodule development . However, ectopic overexpression of miR393, which targets auxin receptors, influenced indeterminate, but not determinate, nodule development (Mao et al, 2013;Turner et al, 2013) and may implicate a diverse role of auxin in nodulation among different legume species. Previously, a relatively high level of miR167 expression was detected in nitrogen-fixing nodules of soybean (Wang et al, 2009;De Luis et al, 2012), which suggests the possibility of a miR167-mediated regulatory mechanism underlying beneficial soybean-rhizobia symbiosis.…”

Quantitative Amplification of Cleaved Ends (qACE) to assay miRNA-directed target cleavage

“…We isolated total RNA from vector control and miR164 overexpressing roots and examined mature miR164 levels by stem-loop qPCR. We observed an 6-fold increase in miR164 over-expressing roots compared to control roots as expected (Figure 2a) 31 . We also examined the expression of GmNAC1b, a 5'-RACE-validated target of miR164 in soybean ( Figure S1) and a close ortholog of AtNAC1 ( Figure S2).…”

GmTIR1/GmAFB3‐based auxin perception regulated by miR393 modulates soybean nodulation

“…Previous studies have shown that miR393a do not affect soybean nodule development and that miR393j‐3p was involved in soybean nodulation through targeting ENOD93 but not auxin receptors (Mao et al ., ; Turner et al ., ; Yan et al ., ). Therefore, we speculated that the miR393c/d/e/f/g showing a different expression pattern during nodulation may be the upstream regulators of auxin receptor genes, such as GmTIR1C in nodulation regulation.…”