Evolution and Stress Responses of CLO Genes and Potential Function of the GhCLO06 Gene in Salt Resistance of Cotton.

Xiaokang Fu,Liang Ma,Baoquan Wang,Shuxun Yu,Pengbo Hao,Boying Lian,Meng Kang,Jianhua Lu,Yonglin Yang,Hengling Wei,Hantao Wang

doi:10.3389/fpls.2021.801239

Abstract

The caleosin (CLO) protein family displays calcium-binding properties and plays an important role in the abiotic stress response. Here, a total of 107 CLO genes were identified in 15 plant species, while no CLO genes were detected in two green algal species. Evolutionary analysis revealed that the CLO gene family may have evolved mainly in terrestrial plants and that biological functional differentiation between species and functional expansion within species have occurred. Of these, 56 CLO genes were identified in four cotton species. Collinearity analysis showed that CLO gene family expansion mainly occurred through segmental duplication and whole-genome duplication in cotton. Sequence alignment and phylogenetic analysis showed that the CLO proteins of the four cotton species were mainly divided into two types: H-caleosins (class I) and L-caleosins (class II). Cis-acting element analysis and quantitative RT–PCR (qRT–PCR) suggested that GhCLOs might be regulated by abscisic acid (ABA) and methyl jasmonate (MeJA). Moreover, transcriptome data and qRT–PCR results revealed that GhCLO genes responded to salt and drought stresses. Under salt stress, gene-silenced plants (TRV: GhCLO06) showed obvious yellowing and wilting, higher malondialdehyde (MDA) content accumulation, and significantly lower activities of superoxide dismutase (SOD) and peroxidase (POD), indicating that GhCLO06 plays a positive regulatory role in cotton salt tolerance. In gene-silenced plants (TRV: GhCLO06), ABA-related genes (GhABF2, GhABI5, and GhNAC4) were significantly upregulated after salt stress, suggesting that the regulation of salt tolerance may be related to the ABA signaling pathway. This research provides an important reference for further understanding and analyzing the molecular regulatory mechanism of CLOs for salt tolerance.

Highlights

Caleosins (CLOs) are calcium-binding proteins encoded by small gene families, sometimes called peroxygenases (PXGs) in databases, and are widely distributed in terrestrial plants (Khalil et al, 2014; Shen et al, 2016; Rahman et al, 2018)
Six motifs were identified in the CLO proteins (Supplementary Figure 2): 68% (38/56) contained motif 4; class I contained motif 1, motif 2 and motif 6; and class II contained motif 4, motif 1, motif 6 and motif 3 but not the GbCLO15. These results showed that the CLO gene family was highly conserved in terms of protein sequence and gene structure, but the structural differences of some genes might lead to functional differentiation
The results showed that the chromosomal distributions of CLO genes in G. arboreum and the corresponding At subgenome of allotetraploid cotton were not identical, which may be caused by chromosome translocation in the process of tetraploid cotton speciation (Hu et al, 2019)

Summary

Introduction

Caleosins (CLOs) are calcium-binding proteins encoded by small gene families, sometimes called peroxygenases (PXGs) in databases, and are widely distributed in terrestrial plants (Khalil et al, 2014; Shen et al, 2016; Rahman et al, 2018). CLO proteins usually contain a highly conserved single calcium-binding EF hand motif, a lipid-binding domain and two invariant heme-coordinating histidine residues (Hanano et al, 2006; Kim et al, 2011; Shen et al, 2014; Rahman et al, 2018). Some CLO subtypes can bind to a variety of cellular bilayer membranes, such as the endoplasmic reticulum (ER) and plasmalemma, through a single transmembrane domain (Partridge and Murphy, 2009; Hanano et al, 2015; Purkrtová et al, 2015)

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Discussion

Conclusion