miR172 Regulates Soybean Nodulation

Abstract

Micro-RNAs (miRNAs) play a pivotal role in the control of gene expression and regulate plant developmental processes. miRNA 172 (miR172) is a conserved miRNA in plants reported to control the expression of genes involved in developmental phase transition, floral organ identity, and flowering time. However, the specific role of miR172 in legume nodulation is undefined. Ectopic expression of soybean miR172 resulted in an increase in nodule numbers in transgenic roots and an increase in the expression of both symbiotic leghemoglobin and nonsymbiotic hemoglobin. These nodules showed higher levels of nitrogenase activity. Further analysis revealed a complex regulatory circuit in which miR156 regulates miR172 expression and controls the level of an AP2 transcription factor. The latter, either directly or indirectly, controls the expression of nonsymbiotic hemoglobin, which is essential for regulating the levels of nodulation.

Soybean miR172c Targets the Repressive AP2 Transcription Factor NNC1 to Activate ENOD40 Expression and Regulate Nodule Initiation

“…These findings indicate that miR172c may be a key regulator of NF perception, bacterial infection, and nodule formation. By 28 DAI, miR172c-overexpressing roots developed significantly more nodules than empty vector control roots (Figure 3G and 3H; Supplemental Figure 4A), consistent with recently reported data (Yan et al, 2013).…”

“…Interestingly, miR172c, miR172d/e, miR172k, and miR172l exhibited high levels of expression in mature nodules ( Figure 1B), suggesting that these evolutionarily close family members may differentially regulate soybean nodulation. The fact that ectopic expression of miR172c (Figure 3) and miR172l (Yan et al, 2013) dramatically increased soybean nodule numbers supports the notion that multiple members of the family modulate nodulation.…”

“…Here, we demonstrated that NNC1, a putative soybean ortholog of Arabidopsis TOE1, is the direct target of miR172c in nodulation ( Figures 6A, 6B, and 7; Supplemental Figures 7A to 7C). Since multiple genes are cleaved by miR172c (Supplemental Figure 6B) and overexpression of glyma11g15650, the closest homolog to NNC1, can also reduce the number of nodules in soybean (Yan et al, 2013), we do not exclude the possibility that other targets are also involved in miR172-mediated regulation of soybean nodulation. Our RACE results demonstrated direct cleavage of target mRNAs by miR172c (Supplemental Figure 6B), but we cannot exclude the possibility that miR172c may also regulate its targets at the posttranslational level.…”

“…In soybean, numerous miRNAs are differentially expressed during nodule organogenesis (Subramanian et al, 2008;Wang et al, 2009;Dong et al, 2013). Studies have shown that overexpression of several of these soybean miRNAs, including isoforms of miR160, miR156, miR1515, and miR172, can affect nodule numbers Turner et al, 2013;Yan et al, 2013). However, to date, there are no reports on the consequences of reducing endogenous miRNA activity on soybean nodule development.…”

An Atlas of Soybean Small RNAs Identifies Phased siRNAs from Hundreds of Coding Genes

“…During nodule differentiation, miR167, which targets ARF6 and ARF8, has a role in auxin signaling/vascular differentiation (Yang et al, 2006) and miR169, which targets transcripts encoding NF-Y transcription factors, in nodule zone differentiation (Simon et al, 2009). miR172, which targets transcripts for AP2 and RAP2 transcription factors (Table 2), has also been reported to regulate nodulation in soybean (Yan et al, 2013), and miR396, for which one target is a PHAS locus (A) A locus on chromosome 20 produces phasiRNAs that are specifically expressed in pollen. These phasiRNAs are triggered by miR4392, the precursor of which located immediately upstream, and also accumulates specifically in pollen.…”