Overexpression of the Suaeda salsa SsNHX1 gene confers enhanced salt and drought tolerance to transgenic Zea mays

Abstract

Maize is one of the most important crops worldwide, but it suffers from salt stress when grown in saline-alkaline soil. There is therefore an urgent need to improve maize salt tolerance and crop yield. In this study, the SsNHX1 gene of Suaeda salsa, which encodes a vacuolar membrane Na + /H + antiporter, was transformed into the maize inbred line 18-599 by Agrobacterium-mediated transformation. Transgenic maize plants overexpressing the SsNHX1 gene showed less growth retardation when treated with an increasing NaCl gradient of up to 1%, indicating enhanced salt tolerance. The improved salt tolerance of transgenic plants was also demonstrated by a significantly elevated seed germination rate (79%) and a reduction in seminal root length inhibition. Moreover, transgenic plants under salt stress exhibited less physiological damage. SsNHX1-overexpressing transgenic maize accumulated more Na + and K + than wild-type (WT) plants particularly in the leaves, resulting in a higher ratio of K + /Na + in the leaves under salt stress. This result revealed that the improved salt tolerance of SsNHX1-overexpressing transgenic maize plants was likely attributed to SsNHX1-mediated localization of Na + to vacuoles and subsequent maintenance of the cytosolic ionic balance. In addition, SsNHX1 overexpression also improved the drought tolerance of the transgenic maize plants, as rehydrated transgenic plants were restored to normal growth while WT plants did not grow normally after dehydration treatment. Therefore, based on our engineering approach, SsNHX1 represents a promising candidate gene for improving the salt and drought tolerance of maize and other crops.

Integrated analysis of long non-coding RNAs and mRNAs reveals the regulatory network of maize seedling root responding to salt stress

“…More and more evidence supported that lncRNAs play significant roles in stress response [ 41 , 46 – 48 ]. Although some functional genes such as ZmNHX , ZmHTK , MIP , and SnRK2 have been proven to participate in the response to salt stress in plants [ 6 , 7 , 49 , 50 ], only a few lncRNAs have been reported to involve salinity stress at a whole transcriptome level. To reveal the salt responsive lncRNAs and the mechanism underlying salt tolerance in maize, we first identified lncRNAs from maize seedling root at different salt treatment stages and normal conditions using whole transcriptome sequencing.…”

“…In maize, large numbers of protein-coding genes involved in salt stress have been reported in previous studies. Overexpression of the Suaeda salsa Na + /H + antiporter gene ( SsNHX1 ) in maize enhances the salt tolerance of the transgenic maize [ 6 ]. ZmSnRK2.11 is a potential negative regulator involved in maize salt stress, which is up-regulated by high salinity.…”

Regulation of AtKUP2 Expression by bHLH and WRKY Transcription Factors Helps to Confer Increased Salt Tolerance to Arabidopsis thaliana Plants

“…Several important Na + transporters such as NHXs, SOS1 and HKTs found in glycophytes as well as in some halophytes are known to mediate salt resistance in plants ( Horie et al, 2009 ; Yang et al, 2009 ; Mishra et al, 2014 ; Hamamoto et al, 2015 ; Ma et al, 2019 ; Al-Harrasi et al, 2020 ). Ectopic expression of some of these Na + transporters in specific targeted tissues or in whole plants have been reported to increase the salinity tolerance of plants ( Yang et al, 2009 ; Li et al, 2011 ; Mian et al, 2011 ; Gao et al, 2012 ; Huang et al, 2018 ; Zhang et al, 2019 ; Al-Harrasi et al, 2020 ), implying that improvement in detoxification mechanisms of Na + possibly is a typical approach to generate salt tolerant crops. In addition, maintenance of high K + /Na + ratio in shoots as wells as roots is essential for salinity tolerance.…”

Research Advances on Molecular Mechanism of Salt Tolerance in Suaeda

“…Vacuolar NHX1 is a membrane protein that plays an important role in the exchange of Na + for H + across the vacuolar membrane, and the segregation of Na + into vacuoles [ 22 ]. It was found that the tonoplast NHX1 was upregulated in S. fruticosa , S. salsa , S. maritima , and S. corniculata after salt stress [ 15 , 17 , 23 , 24 ]. After the SsNHX1/SucNHX1 gene was transferred into rice, maize, and Arabidopsis thaliana , the salt tolerance of the transgenic plants was significantly improved [ 21 , 23 , 24 , 25 ].…”