Morphological, Physiological, and Molecular Bases of Salt Tolerance in Crape Myrtle (Lagerstroemia indica)

Crape myrtle (Lagerstroemia indica and its relatives) is an important summer-flowering plant in numerous countries worldwide. However, there are few reports on salt-tolerant (ST) crape myrtle germplasm resources and their morphological and molecular biological foundations for adaptation to salinized soil, one of the main abiotic stresses in plants. This study identified the salt tolerance characteristics of 19 crape myrtle varieties and created four salt-tolerant germplasms through hybridization. Morphological anatomy and transcriptome analyses clarified that the xylem of the ST variety possessed a high number of vessels with a small lumen. Transcriptome research has indicated that under salt stress conditions, Ca2+, abscisic acid (ABA), and reactive oxygen species (ROS) pathways are involved in salt stress responses. One of the candidate genes LiTIP1;1 (encoding a tonoplast intrinsic protein) was overexpressed in Arabidopsis and the resultant overexpression (OE) lines performed better under CK and 100 mmol∙L−1 NaCl salt stress, but not under 200 mmol∙L−1 NaCl salt stress. Corresponding to physiological traits, genes encoding tubulin and fasciclin-like arabinogalactan proteins (FLAs), which are related to the plasma membrane localization of the cellulose synthase complex, are maintained at higher levels and are induced more by salt. In summary, this research has revealed the morphological, physiological, and molecular bases of ST crape myrtle to a certain extent and has provided a theoretical basis for further screening and breeding of salt-tolerant crape myrtle varieties.