Overexpression of NtCBL5A Leads to Necrotic Lesions by Enhancing Na+ Sensitivity of Tobacco Leaves Under Salt Stress.

Yuhe Sun,Guanshan Liu,Richard G F Visser,C Gerard Van Der Linden,Yuling Bai,Sujuan Shi,Lulu An,Haobao Liu,Jiaping Yuan,Jingjing Mao,Qian Wang,Zhijie Mo

doi:10.3389/fpls.2021.740976

Abstract

Many tobacco (Nicotiana tabacum) cultivars are salt-tolerant and thus are potential model plants to study the mechanisms of salt stress tolerance. The CALCINEURIN B-LIKE PROTEIN (CBL) is a vital family of plant calcium sensor proteins that can transmit Ca2+ signals triggered by environmental stimuli including salt stress. Therefore, assessing the potential of NtCBL for genetic improvement of salt stress is valuable. In our studies on NtCBL members, constitutive overexpression of NtCBL5A was found to cause salt supersensitivity with necrotic lesions on leaves. NtCBL5A-overexpressing (OE) leaves tended to curl and accumulated high levels of reactive oxygen species (ROS) under salt stress. The supersensitivity of NtCBL5A-OE leaves was specifically induced by Na+, but not by Cl−, osmotic stress, or drought stress. Ion content measurements indicated that NtCBL5A-OE leaves showed sensitivity to the Na+ accumulation levels that wild-type leaves could tolerate. Furthermore, transcriptome profiling showed that many immune response-related genes are significantly upregulated and photosynthetic machinery-related genes are significantly downregulated in salt-stressed NtCBL5A-OE leaves. In addition, the expression of several cation homeostasis-related genes was also affected in salt-stressed NtCBL5A-OE leaves. In conclusion, the constitutive overexpression of NtCBL5A interferes with the normal salt stress response of tobacco plants and leads to Na+-dependent leaf necrosis by enhancing the sensitivity of transgenic leaves to Na+. This Na+ sensitivity of NtCBL5A-OE leaves might result from the abnormal Na+ compartmentalization, plant photosynthesis, and plant immune response triggered by the constitutive overexpression of NtCBL5A. Identifying genes and pathways involved in this unusual salt stress response can provide new insights into the salt stress response of tobacco plants.

Highlights

Soil salinity causes serious yield losses because of its widespread occurrence and severe effects on crop physiology and metabolism (Munns and Tester, 2008)
Our results indicate that constitutive overexpression of NtCBL5A leads to Na+-dependent leaf necrosis by enhancing the sensitivity of transgenic tobacco leaves to Na+
The coding sequence (CDS) of NtCBL5A is identical to the CDS of NsylCBL5 and has 28 nucleotide differences with the CDS of NtomCBL5 (NCBI reference sequence number: XM_018767788.1; Supplementary Figure S1A)

Summary

Introduction

Soil salinity causes serious yield losses because of its widespread occurrence and severe effects on crop physiology and metabolism (Munns and Tester, 2008). Salt stress can be divided into two phases, the first of which is the osmotic or water-deficit stress (Munns, 2005; Van Zelm et al, 2020). The osmotic stress can be measured as a rapid inhibition of the rate of expansion of young leaves, while ion toxicity causes stress-induced senescence of older leaves due to either high leaf Na+ concentrations or low tolerance of the accumulated Na+ (Munns and Tester, 2008)

Methods

Results

Conclusion