Drought Response in Rice: The miRNA Story

Abstract

As a semi-aquatic plant, rice requires water for proper growth, development, and orientation of physiological processes. Stress is induced at the cellular and molecular level when rice is exposed to drought or periods of low water availability. Plants have existing defense mechanisms in planta that respond to stress. In this review we examine the role played by miRNAs in the regulation and control of drought stress in rice through a summary of molecular studies conducted on miRNAs with emphasis on their contribution to drought regulatory networks in comparison to other plant systems. The interaction between miRNAs, target genes, transcription factors and their respective roles in drought-induced stresses is elaborated. The cross talk involved in controlling drought stress responses through the up and down regulation of targets encoding regulatory and functional proteins is highlighted. The information contained herein can further be explored to identify targets for crop improvement in the future.

Keywords: antioxidant defense; drought; growth and development; hormone; miRNA; osmoregulation; rice; senescence.

Figure 1

The regulation of microRNA under drought stress by phytohormones in rice. The legend above provides elaboration on the functions depicted by each arrow. The above miRNAs were identified post treatment with ABA and drought. Their up or down regulation resulted in a positive or negative effect on target transcription factors (auxin response factor (ARF), NAC, MYB, Nuclear factor Y (NFY), and DDB1 binding WD40 (DWD)). These interactions resulted in either an increase or decrease in the expression of drought stress related genes such as GH3. Hormones such as auxin, Abscisic acid (ABA), gibberellin (GA), and brassinosteroid (BR) play an important role in drought response. The processes affected by the interaction between the miRNA-Transcription Factor-gene complex is elaborated within the text.

Figure 2

The regulation of microRNA under drought stress involving growth, development, photosynthesis and respiration. The legend above provides elaboration on the functions depicted by each arrow. The above miRNAs were identified under drought stress and their regulation resulted in a positive or negative effect on target transcription factors (ARF, NAC, GRF, HD-ZIP, SPL, MYB, NFY) or genes. These interactions resulted in either an increase or decrease in the expression of genes related to growth and development, photosynthesis, and respiration for better adaptation under drought. The interactions between the miRNAs-Transcription Factors-gene complex has been elaborated on within the text. The putative microRNAs (n-006, n-192, n-063, n-137, and n-024) are novel microRNAs from rice.

Figure 3

The regulation of microRNA under drought stress involving senescence, antioxidant defense and osmoregulation. The legend above provides elaboration on the functions of each arrow. The above miRNAs were identified under drought stress and their regulation resulted in a positive or negative effect on target transcription factors (ARF, NAC, ZF, HAP-2, SPL) or genes. These interactions resulted in either an increase or decrease in the expression of genes related to senescence, oxidative stress, and osmoprotection for better adaptation under drought.

Figure 4

The regulation of drought tolerance and response in rice. The regulation of drought tolerance and response by key miRNAs via auxin, ABA, GA, BR, and ethylene. Processes like programmed cell death, senescence, ROS homeostasis, growth and development, photosynthesis, and yield are regulated by miRNAs through its respective targets for better drought tolerance. The colored arrows show the regulation of miRNA by different phytohormones (yellow: GA, blue: ABA, orange: auxin, green: BR, purple: ethylene). The black arrows indicate the regulation of target genes/transcription factors by miRNA and the regulation of drought responses by the target genes/transcription factors. The black ovals represent target genes/transcription factors).