AUTHOR=Mao Jingjing , Yuan Jiaping , Mo Zhijie , An Lulu , Shi Sujuan , Visser Richard G. F. , Bai Yuling , Sun Yuhe , Liu Guanshan , Liu Haobao , Wang Qian , van der Linden C. Gerard 

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

JOURNAL=Frontiers in Plant Science

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.740976

DOI=10.3389/fpls.2021.740976

ISSN=1664-462X

ABSTRACT=<p>Many tobacco (<italic>Nicotiana tabacum</italic>) 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 Ca<sup>2+</sup> signals triggered by environmental stimuli including salt stress. Therefore, assessing the potential of <italic>NtCBL</italic> for genetic improvement of salt stress is valuable. In our studies on <italic>NtCBL</italic> members, constitutive overexpression of <italic>NtCBL5A</italic> was found to cause salt supersensitivity with necrotic lesions on leaves. <italic>NtCBL5A</italic>-overexpressing (OE) leaves tended to curl and accumulated high levels of reactive oxygen species (ROS) under salt stress. The supersensitivity of <italic>NtCBL5A</italic>-OE leaves was specifically induced by Na<sup>+</sup>, but not by Cl<sup>−</sup>, osmotic stress, or drought stress. Ion content measurements indicated that <italic>NtCBL5A</italic>-OE leaves showed sensitivity to the Na<sup>+</sup> 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 <italic>NtCBL5A</italic>-OE leaves. In addition, the expression of several cation homeostasis-related genes was also affected in salt-stressed <italic>NtCBL5A</italic>-OE leaves. In conclusion, the constitutive overexpression of <italic>NtCBL5A</italic> interferes with the normal salt stress response of tobacco plants and leads to Na<sup>+</sup>-dependent leaf necrosis by enhancing the sensitivity of transgenic leaves to Na<sup>+</sup>. This Na<sup>+</sup> sensitivity of <italic>NtCBL5A</italic>-OE leaves might result from the abnormal Na<sup>+</sup> compartmentalization, plant photosynthesis, and plant immune response triggered by the constitutive overexpression of <italic>NtCBL5A</italic>. Identifying genes and pathways involved in this unusual salt stress response can provide new insights into the salt stress response of tobacco plants.</p>