MicroRNA Zma-miR528 Versatile Regulation on Target mRNAs during Maize Somatic Embryogenesis.

Eduardo Luján-Soto,Tzvetanka D Dinkova,Vasti T Juárez-González,José L Reyes

doi:10.3390/ijms22105310

Eduardo Luján-Soto, Tzvetanka D Dinkova + Show 2 more

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https://doi.org/10.3390/ijms22105310

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Abstract

MicroRNAs (miRNAs) are small non-coding RNAs that regulate the accumulation and translation of their target mRNAs through sequence complementarity. miRNAs have emerged as crucial regulators during maize somatic embryogenesis (SE) and plant regeneration. A monocot-specific miRNA, mainly accumulated during maize SE, is zma-miR528. While several targets have been described for this miRNA, the regulation has not been experimentally confirmed for the SE process. Here, we explored the accumulation of zma-miR528 and several predicted targets during embryogenic callus induction, proliferation, and plantlet regeneration using the maize cultivar VS-535. We confirmed the cleavage site for all tested zma-miR528 targets; however, PLC1 showed very low levels of processing. The abundance of zma-miR528 slightly decreased in one month-induced callus compared to the immature embryo (IE) explant tissue. However, it displayed a significant increase in four-month sub-cultured callus, coincident with proliferation establishment. In callus-regenerated plantlets, zma-miR528 greatly decreased to levels below those observed in the initial explant. Three of the target transcripts (MATE, bHLH, and SOD1a) showed an inverse correlation with the miRNA abundance in total RNA samples at all stages. Using polysome fractionation, zma-miR528 was detected in the polysome fraction and exhibited an inverse distribution with the PLC1 target, which was not observed at total RNA. Accordingly, we conclude that zma-miR528 regulates multiple target mRNAs during the SE process by promoting their degradation, translation inhibition or both.

Highlights

Among the distinctive features of plants, the capacity to generate an embryo by several routes is one of their most remarkable abilities
Zma-miR528 mRNA targets were predicted using the psRNA Target program (Supplementary Materials, Additional File 1, Table S1) with the expectation threshold set at ≤ 4 to obtain a stringent search with high coverage [21]
The regulation exerted by miRNAs is essential for controlling key processes in somatic embryogenesis (SE) [9,39,40]

Summary

Introduction

Among the distinctive features of plants, the capacity to generate an embryo by several routes is one of their most remarkable abilities. In the late 1950s, carrot somatic cells exposed to a synthetic medium containing auxins and other phytohormones produced large numbers of embryos; this in vitro reprogramming, known as somatic embryogenesis (SE), was later found to be common in many plant species and could vary depending on many factors such as the plant genotype, the identity of the initial cells, and the usage of different combinations of growth regulators. Regardless of these singularities, SE can be used for the mass production of economically important plants, clonal propagation, germplasm conservation, protoplast culture, and genetic improvement of agronomic traits [1]. Biogenesis enzymes successively process the primary transcripts into functional mature miRNAs that promote their complementary target silencing by cleavage or translational inhibition [3]

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