MicroRNA156 (miR156) regulates a network of genes that affect plant growth
and development. Previous studies have generated alfalfa (Medicago sativa)
plants that overexpress homologous miR156 (MsmiR156OE), which exhibited
increased vegetative yield, delayed flowering, and longer roots. A team of
scientists from the Agriculture and Agri-Food Canada led by Banyar Aung
aimed to explain the effect of miR156 on the root system, including effect
on nodulation and nitrogen fixation.

The team found that MsmiR156 overexpression increases root regeneration
capacity in alfalfa, but with little effect on root biomass at the early
stages of root development. MsmiR156 also promotes nitrogen fixation
activity by upregulating expression of nitrogenase-related genes such as
FixK, NifA, and RpoH in roots inoculated with Sinorrhizobium meliloti.

Further analysis of MsmiR156OE alfalfa roots identified differentially
expressed genes belonging to different functional categories, including
plant cell wall organization and response to water stress. Analysis also
revealed the effects of miR156 on genes involved in nodulation, root
development, and phytohormone biosynthesis.

These findings suggest that miR156 regulates root development and nitrogen
fixation activity and thus it is vital in the improvement of alfalfa and
other crops.

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