Characterization of Brassinazole resistant (BZR) gene family and stress induced expression in Eucalyptus grandis

Abstract

Brassinosteroids (BRs) are a group of plant hormones which play a pivotal role in modulating cell elongation, stress responses, vascular differentiation and senescence. In response to BRs, BRASSINAZOLE-RESISTANT (BZR) transcription factors (TFs) accumulate in the nucleus, where they modulate thousands of target genes and coordinate many biological processes, especially in regulating defense against biotic and abiotic stresses. In this study, 6 BZR TFs of Eucalyptus grandis (EgrBZR) from a genome-wide survey were characterized by sequence analysis and expression profiling against several abiotic stresses. The results showed that BZR gene family in Eucalyptus was slightly smaller compared to Populus and Arabidopsis, but all phylogenetic groups were represented. Various systematic in silico analysis of these TFs validated the basic properties of BZRs, whereas comparative studies showed a high degree of similarity with recognized BZRs of other plant species. In the organ-specific expression analyses, 4 EgrBZRs were expressed in vascular tissue indicating their possible functions in wood formation. Meanwhile, almost all EgrBZR genes showed differential transcript abundance levels in response to exogenously applied BR, MeJA, and SA, and salt and cold stresses. Besides, protein interaction analysis showed that all EgrBZR genes were associated with BR signaling directly or indirectly. These TFs were proposed as transcriptional activators or repressors of abiotic stress response and growth and development pathways of E. grandis by participating in BR signaling processes. These findings would be helpful in resolving the regulatory mechanism of EgrBZRs in stress resistance conditions but require further functional study of these potential TFs in Eucalyptus.

Keywords: Abiotic stress; BZR; Brassinosteroids; Eucalyptus; Gene expression.

Fig. 1

Schematic representation of motifs distribution identified in E. grandis BZR proteins. Different motifs are indicated by different colors. The names of all members are shown on the left side of the figure, along with their phylogenetic relatedness

Fig. 2

Alignment of deduced amino acid sequences of EgrBZR proteins. Solid boxes represent DUF822 and C-terminal domains, respectively. Black lines indicate serine rich phosphorylation sites among the six EgrBZR proteins. Numbers at the left and right indicate the positions of amino acid residues

Fig. 3

Phylogenetic tree showing the relatedness of the deduced full-length amino acid sequences of six EgrBZR proteins and all BZR family proteins of Arabidopsis (prefixed with ‘At’) and Populus (prefixed with ‘Ptr’)

Fig. 4

Chromosomal locations of E. grandis BZR genes along chromosomes. Chromosome numbers (e.g., Chr04 to Chr06, and Chr08) are indicated above the chromosomes. The plus (+) and minus (−) signs following gene names represent forward and reverse orientation of the respective genes. Gene positions and chromosome sizes can be estimated using the scale (in Megabases, Mb) to the left of the figure

Fig. 5

Expression analysis of six BZR genes in different tissues of E. grandis x E. urophylla. Color bars at the top indicate the expression levels: red represents high expression and green represents low expression

Fig. 6

qRT-PCR expression analysis of EgrBZR genes under BR, MeJA, and SA treatments in leaves of E. grandis. The error bars represent standard error of the means of three independent replicates. The asterisk indicates a significant difference (P < 0.05) compared with control group according to Duncan’s Test

Fig. 7

qRT-PCR expression analysis of EgrBZR genes under cold and salt treatments in leaves of E. grandis. The error bars represent standard error of the means of three independent replicates. The asterisk indicates a significant difference (P < 0.05) compared with control group according to Duncan’s Test

Fig. 8

Interaction network of homologs of six EgrBZR TFs and the related genes in Arabidopsis. Stronger associations are represented by thicker lines