Subtly Manipulated Expression of ZmmiR156 in Tobacco Improves Drought and Salt Tolerance Without Changing the Architecture of Transgenic Plants.

Tao Kang,Yue Liu,Xiao-Tong Guo,Bei Li,Hong-Xia Zhang,Chun-Yan Yu,Yan Bao,Wei-Meng Song

doi:10.3389/fpls.2019.01664

Abstract

Plants in the juvenile state are more tolerant to adverse conditions. Constitutive expression of MicroRNA156 (miR156) prolonged the juvenile phase and increased resistance to abiotic stress, but also affected the architecture of transgenic plants. In this study, we investigated the possibility of subtle manipulation of miR156 expression in flowering plants, with the goal to increase tolerance to abiotic stress without altering the normal growth and development of transgenic plants. Transgenic tobacco plants expressing ZmmiR156 from maize were generated, driven either by the cauliflower mosaic virus (CaMV) 35S promoter or the stress-inducible ZmRab17 promoter. Expression of ZmmiR156 led to improved drought and salt tolerance in both 35S::MIR156 and Rab17::MIR156 transgenic plants, as shown by more vigorous growth, greater biomass production and higher antioxidant enzyme expression after a long period of drought or salt treatment, when compared to wild type and transgenic vector control plants. However, constitutive expression of ZmmiR156 also resulted in retarded growth, increased branching and delayed flowering of transgenic plants. These undesirable developmental changes could be mitigated by using the stress-inducible ZmRab17 promoter. Furthermore, under drought or salt stress conditions, expression of ZmmiR156 reduced the transcript level of NtSPL2 and NtSPL9, the genes potentially targeted by ZmmiR156, as well as that of CP1, CP2, and SAG12, the senescence-associated genes in tobacco. Collectively, our results indicate that ZmmiR156 can be temporally manipulated for the genetic improvement of plants resistant to various abiotic stresses.

Highlights

Unlike animals, plants are sessile organisms that cannot avoid or flee from adverse conditions
We explored whether subtly manipulating the expression of ZmmiR156 from maize (Zea mays) in tobacco would improve the tolerance to drought and salt stresses but cause no significant effects on the regular growth and development of transgenic plants
Since miR156 plays a pivotal role in regulating the transition of plants from vegetative growth to reproductive phase, we further examined the effect of salt stress on the growth of adult plants expressing ZmmiR156

Summary

Introduction

Plants are sessile organisms that cannot avoid or flee from adverse conditions. They have developed a series of strategies to cope with or tolerate different environmental stresses. As one of the conserved miRNA families in higher plants, miR156 is highly expressed in seedlings and decreased during the juvenile-to-adult transition (Wang et al, 2011). In maize, enhanced expression of miR156b/c dramatically increased the branch numbers of transgenic plants (Chuck et al, 2007). Overexpression of miR156 reduced the expression of miR156targeted SPL genes, and prolonged the juvenile phase of transgenic poplar (Wang et al, 2011). Overexpression of GmmiR156b in soybean improved shoot architecture and significantly increased the numbers of long branches, nodes and pods, leading to improved grain yield in transgenic plants (Sun et al, 2019)

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