Molecular Aspects of MicroRNAs and Phytohormonal Signaling in Response to Drought Stress: A Review

Abstract

Phytohormones play an essential role in plant growth and development in response to environmental stresses. However, plant hormones require a complex signaling network combined with other signaling pathways to perform their proper functions. Thus, multiple phytohormonal signaling pathways are a prerequisite for understanding plant defense mechanism against stressful conditions. MicroRNAs (miRNAs) are master regulators of eukaryotic gene expression and are also influenced by a wide range of plant development events by suppressing their target genes. In recent decades, the mechanisms of phytohormone biosynthesis, signaling, pathways of miRNA biosynthesis and regulation were profoundly characterized. Recent findings have shown that miRNAs and plant hormones are integrated with the regulation of environmental stress. miRNAs target several components of phytohormone pathways, and plant hormones also regulate the expression of miRNAs or their target genes inversely. In this article, recent developments related to molecular linkages between miRNAs and phytohormones were reviewed, focusing on drought stress.

The Rootstock Genotypes Determine Drought Tolerance by Regulating Aquaporin Expression at the Transcript Level and Phytohormone Balance

“…Our data suggest a clear relationship between ABA and both g s and Kh plant , where an increase in ABA triggers a decrease in g s and Kh plant until reaching a plateau ( Figure 4 D,F). Under WW conditions, either ABA and ACC concentrations, both related to drought resistance [ 47 , 78 , 79 , 80 , 81 ], kept similar concentration for all the studied rootstocks, both in the leaf and in the xylem. However, under WS conditions, increases in both phytohormones were rootstock-dependent.…”

“…Several studies have shown that GA and CK are involved in plant photosynthesis regulation and source/sink balance [ 79 , 81 , 87 , 88 , 89 ]. Concretely, the movement of CK in the transpiration stream from the roots to the shoots stimulates the expression of photosynthesis genes [ 90 ].…”

“…SA accumulates before infection and is associated with biotrophic factors, while JA accumulation is after infection and is related to necrotrophic pathogens [ 97 , 98 ]. Moreover, their role in abiotic stress response in plants has been suggested [ 79 , 81 ]. In this study, the WS treatment resulted in a null on the leaf JA concentration or an increase in its xylem concentration.…”

“…In spite of this, it has been previously reported that phytohormone concentrations in leaf extracts were positively and significantly correlated with those of xylem sap in grafted tomato plants [ 100 ], and the inverse correlation was observed in this study for SA, which could indicate that this phytohormone first accumulates in the xylem and is then transported to the leaf. It may explain the contrasting results observed in the literature for the different species, such as chickpeas, tomatoes, Arabidopsis , or Brassica sp., concerning SA response to WS [ 78 , 79 ]. Some studies have shown that high SA concentrations affect A N enhancement, antioxidant production, and stomatal regulation.…”

“…However, disparate results have been observed for IAA responses to drought. Hussain et al [ 99 ] showed a negative IAA response in Arabidopsis thaliana , while Ahmad et al [ 79 ] reported IAA increases in Ozyria sativa . In grapevine, different studies also reported different IAA responses induced by WS [ 50 , 82 , 102 ].…”