The Divergent Roles of the Rice bcl-2 Associated Athanogene (BAG) Genes in Plant Development and Environmental Responses.

Hailian Zhou,Xiaoshuang Wei,Jihong Wang,Jiaying Li,Lingqiang Wang,Lihua Hu,Ziwei He,Xueyuan Liu,Jibin Wang,Guosheng Xie,Mingzheng Duan

doi:10.3390/plants10102169

Abstract

Bcl-2-associated athanogene (BAG), a group of proteins evolutionarily conserved and functioned as co-chaperones in plants and animals, is involved in various cell activities and diverse physiological processes. However, the biological functions of this gene family in rice are largely unknown. In this study, we identified a total of six BAG members in rice. These genes were classified into two groups, OsBAG1, -2, -3, and -4 are in group I with a conserved ubiquitin-like structure and OsBAG5 and -6 are in group Ⅱ with a calmodulin-binding domain, in addition to a common BAG domain. The BAG genes exhibited diverse expression patterns, with OsBAG4 showing the highest expression level, followed by OsBAG1 and OsBAG3, and OsBAG6 preferentially expressed in the panicle, endosperm, and calli. The co-expression analysis and the hierarchical cluster analysis indicated that the OsBAG1 and OsBAG3 were co-expressed with primary cell wall-biosynthesizing genes, OsBAG4 was co-expressed with phytohormone and transcriptional factors, and OsBAG6 was co-expressed with disease and shock-associated genes. β-glucuronidase (GUS) staining further indicated that OsBAG3 is mainly involved in primary young tissues under both primary and secondary growth. In addition, the expression of the BAG genes under brown planthopper (BPH) feeding, N, P, and K deficiency, heat, drought and plant hormones treatments was investigated. Our results clearly showed that OsBAGs are multifunctional molecules as inferred by their protein structures, subcellular localizations, and expression profiles. BAGs in group I are mainly involved in plant development, whereas BAGs in group II are reactive in gene regulations and stress responses. Our results provide a solid basis for the further elucidation of the biological functions of plant BAG genes.

Highlights

The b-cell lymphoma 2 (Bcl-2)-associated athanogene (BAG) family is evolutionarily conserved and function as co-chaperones [1,2,3]
In addition to the BAG domain (BD), the OsBAG1–4 contained a ubiquitin-like (UBL) structure, whereas OsBAG5 and -6 harbored a calmodulin-binding domain, a novel feature only found in plant Bcl-2-associated athanogene (BAG) proteins, indicating possible divergent mechanisms associated with plant-specific functions (Table 1; Figure 1A)
The OsBAG gene members were distributed on six chromosomes of rice individually, and no tandem Plants 2021, 10, x FOR PEER REVIEW duplication set was discovered, which was different with the Arabidopsis that had7 ofof 1u9r BAGs on chromosome V likely arising from local gene duplication (Additional File S5)

Summary

Introduction

The Bcl-2-associated athanogene (BAG) family is evolutionarily conserved and function as co-chaperones [1,2,3]. Plant BAG proteins are multifunctional, as they inhibit several cell-death-mediated processes and appear to function in cyto-protection under both stress conditions and plant development [2,3,10,13,14]. A grape Bcl-2-associated athanogenea (HSG1) is not expressed under normal conditions, but the expression level in leaves and fruits increases sharply under heat stress and promotes floral transition by activating CONSTANS expression in transgenic Arabidopsis plant [18]. A plenty of evidence proofed that plant BAG proteins have a similar modulating mechanism to that of animal BAGs, and they can interact with other proteins as molecular bridges to mediate diverse cell events

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Results

Conclusion