Genome-wide identification of bHLH transcription factors and functional analysis in salt gland development of the recretohalophyte sea lavender (Limonium bicolor)

Abstract

Transcription factors with basic helix-loop-helix (bHLH) structures regulate plant growth, epidermal structure development, metabolic processes, and responses to stress extensively. Sea lavender (Limonium bicolor) is a recretohalophyte with unique salt glands in the epidermis that make it highly resistant to salt stress, contributing to the improvement of saline lands. However, the features of the bHLH transcription factor family in L. bicolor are largely unknown. Here, we systematically analyzed the characteristics, localization, and phylogenetic relationships of 187 identified bHLH family genes throughout the L. bicolor genome, as well as their cis-regulatory promoter elements, expression patterns, and key roles in salt gland development or salt tolerance by genetic analysis. Nine verified L. bicolor bHLH genes are expressed and the encoded proteins function in the nucleus, among which the proteins encoded by Lb2G14060 and Lb1G07934 also localize to salt glands. Analysis of CRISPR-Cas9-generated knockout mutants and overexpression lines indicated that the protein encoded by Lb1G07934 is involved in the formation of salt glands, salt secretion, and salt resistance, indicating that bHLH genes strongly influence epidermal structure development and stress responses. The current study lays the foundation for further investigation of the effects and functional mechanisms of bHLH genes in L. bicolor and paves the way for selecting salt-tolerance genes that will enhance salt resistance in crops and for the improvement of saline soils.

Acknowledgements

The National Natural Science Research Foundation of China (NSFC, projects 32370304 and 32170301) and the MOE Layout Foundation of Humanities and Social Sciences (21YJAZH108) supported this study.

Author contributions

Conceptualization: F.Y.; Data curation: X.W.; Funding acquisition: B.W. and F.Y.; Writing - original draft: X.W.; Writing - review & editing: B.W. and F.Y.

Conflict of interest

The authors state that they do not have conflicts of interest related to this work.

Data availability

The genome and transcriptome data underlying this article are available in NCBI at https://www.ncbi.nlm.nih.gov/bioproject/, and can be accessed with BioProject numbers PRJNA753199, PRJNA752802, and PRJNA752940. The data underlying this article will be shared on reasonable request to the corresponding author.

Supplementary data

Supplementary data are available at Horticulture Research online.

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