Abstract
Members of the plant Heme Activator Protein (HAP) or NUCLEAR FACTOR Y (NF-Y) are trimeric transcription factor complexes composed of the NF-YA, NF-YB and NF-YC subfamilies. They bind to the CCAAT box in the promoter regions of the target genes and regulate gene expressions. Plant NF-Ys were reported to be involved in adaptation to several abiotic stresses as well as in development. In silico analysis of Sorghum bicolor genome resulted in the identification of a total of 42 NF-Y genes, among which 8 code for the SbNF-YA, 19 for SbNF-YB and 15 for the SbNF-YC subunits. Analysis was also performed to characterize gene structures, chromosomal distribution, duplication status, protein subcellular localizations, conserved motifs, ancestral protein sequences, miRNAs and phylogenetic tree construction. Phylogenetic relationships and ortholog predictions displayed that sorghum has additional NF-YB genes with unknown functions in comparison with Arabidopsis. Analysis of promoters revealed that they harbour many stress-related cis-elements like ABRE and HSE, but surprisingly, DRE and MYB elements were not detected in any of the subfamilies. SbNF-YA1, 2, and 6 were found upregulated under 200 mM salt and 200 mM mannitol stresses. While NF-YA7 appeared associated with high temperature (40°C) stress, NF-YA8 was triggered by both cold (4°C) and high temperature stresses. Among NF-YB genes, 7, 12, 15, and 16 were induced under multiple stress conditions such as salt, mannitol, ABA, cold and high temperatures. Likewise, NF-YC 6, 11, 12, 14, and 15 were enhanced significantly in a tissue specific manner under multiple abiotic stress conditions. Majority of the mannitol (drought)-inducible genes were also induced by salt, high temperature stresses and ABA. Few of the high temperature stress-induced genes are also induced by cold stress (NF-YA2, 4, 6, 8, NF-YB2, 7, 10, 11, 12, 14, 16, 17, NF-YC4, 6, 12, and 13) thus suggesting a cross talk among them. This work paves the way for investigating the roles of diverse sorghum NF-Y proteins during abiotic stress responses and provides an insight into the evolution of diverse NF-Y members.
Highlights
Nuclear Factor Y (NF-Y), known as heme activator protein (HAP) or CCAAT-binding factor (CBF) is a ubiquitous, complex, heterotrimeric transcription factor
The predicted 8 NF-YA, 19 NF-YB and 15 NF-YC genes were named as SbNF-YA1 to SbNF-YA8, SbNF-YB1 to SbNF-YB19 and SbNF-YC1 to SbNF-YC15 respectively
Based on the presence of conserved NF-YA, NF-YB and NF-YC domains, the predicted SbNF-Y family of proteins was considered for identification as a member
Summary
Nuclear Factor Y (NF-Y), known as heme activator protein (HAP) or CCAAT-binding factor (CBF) is a ubiquitous, complex, heterotrimeric transcription factor It is evolutionarily conserved in all plants with three distinct subunits called NF-YA or HAP2, NF-YB or HAP3/ CBF-A and NF-YC or HAP5/CBF-C [1]. Several members of the NF-Y subfamilies play a vital role in a wide array of developmental processes but in tolerance to abiotic stresses as well. Ni et al [19] reported that GmNF-YA3, a target gene of miR169, is a positive regulator of plant tolerance to drought stress in A. thaliana. Incorporation of several NF-YB and NF-YC genes improved drought stress tolerance in diverse plants like Arabidopsis, maize, poplar and rice [10, 22, 23, 24]. In Brachypodium distachyon 36 (7 NF-YA, 17 NF-YB, and 12 NF-YC) [29]; in Brassica napus 33 (14 NF-YA, 14 NF-YB, 5 NF-YC) [30]; in Setaria italica 39 (10 NF-YA, 15 NF-YB and 14 NF-YC) [31]; in Glycine max 68 (21 NF-YA, 32 NF-YB, 15 NF-YC) [32]; in Prunus mume 29 [33]; in Ricinus communis 25 (6 NF-YA, 12 NF-YB and 7 NF-YC) [34]; in Citrus sinensis and C. clemantia 22 (6 NF-YA, 11 NF-YB, 5 NF-YC) [35] were characterised
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