Abstract
In recent years, it has become readily accepted among interdisciplinary agriculturalists that the current global crop yield to land capability ratio is significantly insufficient to achieve food security for the predicted population of 9.5 billion individuals by the year 2050. This issue is further compounded by the: (1) food versus biofuel debate; (2) decreasing availability of arable land; (3) required reductions to the extensive and ongoing environmental damage caused by either poor agricultural practices or agriculture expansion, and; (4) increasingly unfavorable (duration and severity) crop cultivation conditions that accompany man-made climate change, driven by ever-expanding urbanization and its associated industrial practices. Mounting studies are repeatedly highlighting the critical importance of linking genotypes to agronomically beneficial phenotypes and/or using a molecular approach to help address this global crisis, as “simply” clearing the remaining natural ecosystems of the globe for the cultivation of additional, non-modified crops is not efficient, nor is this practice sustainable. The majority of global food crop production is sourced from a small number of members of the Poaceae family of grasses, namely; maize (Zea mays L.), wheat (Triticum aestivum L.) and rice (Oryza sativa L.). It is, therefore, of significant concern that all three of these Poaceae grass species are susceptible to a range of abiotic stresses, including drought and salt stress. Highly conserved among monocotyledonous and dicotyledonous plant species, microRNAs (miRNAs) are now well-established master regulators of gene expression, influencing all aspects of plant development, mediating defense responses against pathogens and adaptation to environmental stress. Here we investigate the variation in the abundance profiles of six known abiotic stress-responsive miRNAs, following exposure to salt and drought stress across these three key Poaceae grass crop species as well as to compare these profiles to those obtained from the well-established genetic model plant species, Arabidopsis thaliana (L.) Heynh. Additionally, we outline the variables that are the most likely primary contributors to instances of differential miRNA abundance across the assessed species following drought or salt stress exposure, specifically; (1) identifying variations in the experimental conditions and/or methodology used to assess miRNA abundance, and; (2) the distribution of regulatory transcription factor binding sites within the putative promoter region of a MICRORNA (MIR) gene that encodes the highly conserved, stress-responsive miRNA. We also discuss the emerging role that non-conserved, species-specific miRNAs play in mediating a plant’s response to drought or salt stress.
Highlights
The global human population relies heavily on the major Poaceae cereal grasses, maize (Zea mays L.), wheat (Triticum aestivum L.), and rice (Oryza sativa L.), for their daily calorie intake [1,2]
To highlight the negative impacts accompanying the abiotic stresses, drought and salt stress, abiotic stresses that significantly reduce global agricultural output annually, this review focuses on key agricultural crop producing regions of the United States of America (US) and Australia, the crop producing areas of the west coast of the US that rely on irrigation sourced from the Colorado
While not always the case, the accumulation profile of an abiotic stress-responsive miRNA can vary considerably across different plant species following exposure to drought or salt stress. This variation is prevalent when attempting to translate research findings made in the classic genetic model plant species, Arabidopsis, to agronomically significant crops, such as maize, wheat or rice
Summary
The global human population relies heavily on the major Poaceae cereal grasses, maize (Zea mays L.), wheat (Triticum aestivum L.), and rice (Oryza sativa L.), for their daily calorie intake [1,2]. As one of the largest contributing factors to greenhouse gas emissions and biodiversity reduction, this practice reinforces the urgent need for an alternate, molecular-based approach that targets crop yield maximization. In addition to their central role in regulating developmental gene expression, plant microRNAs (miRNAs), and miRNA-directed gene expression regulation, have more recently been identified as key regulators of plant metabolism, pathogen defense and for a plant to mount an effective adaptive response to abiotic stress [19,20,21]. The degree of variation in the response of stress-responsive miRNAs to abiotic stress, becomes an even more pronounced challenge when attempting to translate findings made in the traditional genetic model plant species, Arabidopsis, to agronomically important Poaceae grass crop species
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