Abstract
NAC [no apical meristem (NAM), Arabidopsis transcription activation factor [ATAF1/2] and cup-shaped cotyledon (CUC2)] proteins is one of the largest groups of plant specific transcription factors and plays a crucial role in plant growth, development, and adaption to the environment. Currently, no information is known about the NAC family in cassava. In this study, 96 NAC genes (MeNACs) were identified from the cassava genome. Phylogenetic analysis of the NACs from cassava and Arabidopsis showed that MeNAC proteins can be clustered into 16 subgroups. Gene structure analysis found that the number of introns of MeNAC genes varied from 0 to 5, with the majority of MeNAC genes containing two introns, indicating a small gene structure diversity of cassava NAC genes. Conserved motif analysis revealed that all of the identified MeNACs had the conserved NAC domain and/or NAM domain. Global expression analysis suggested that MeNAC genes exhibited different expression profiles in different tissues between wild subspecies and cultivated varieties, indicating their involvement in the functional diversity of different accessions. Transcriptome analysis demonstrated that MeNACs had a widely transcriptional response to drought stress and that they had differential expression profiles in different accessions, implying their contribution to drought stress resistance in cassava. Finally, the expression of twelve MeNAC genes was analyzed under osmotic, salt, cold, ABA, and H2O2 treatments, indicating that cassava NACs may represent convergence points of different signaling pathways. Taken together, this work found some excellent tissue-specific and abiotic stress-responsive candidate MeNAC genes, which would provide a solid foundation for functional investigation of the NAC family, crop improvement and improved understanding of signal transduction in plants. These data bring new insight on the complexity of the transcriptional control of MeNAC genes and support the hypothesis that NACs play an important role in plant growth, development, and adaption of environment.
Highlights
The NAC family (NAM, no apical meristem; ATAF, Arabidopsis transcription activation factor; and CUC, cup-shaped cotyledon) is one of the largest groups of plant-specific transcription factors [1, 2, 3, 4]
There is abundant evidence indicating that NAC proteins play crucial roles in various aspects of plant growth and development, and adaption to the environment [14, 15], including maintenance of the shoot apical meristem [1, 16], cell division and expansion [17], nutrient remobilization [18], flower formation [19], lateral root development [20, 21], leaf senescence [22, 23, 24, 25, 26, 27], secondary cell wall biosynthesis [3, 28], fiber development [29], seed development [30], and response to pathogen infection [9, 12, 31, 32, 33, 34] and abiotic stresses [15, 26, 33, 35, 36, 37, 38, 39]
Conserved domain analysis further confirmed that all of the NACs contain the NAC domain or NAM domain at the N-terminus that are the basic characteristics of NAC family
Summary
The NAC family (NAM, no apical meristem; ATAF, Arabidopsis transcription activation factor; and CUC, cup-shaped cotyledon) is one of the largest groups of plant-specific transcription factors [1, 2, 3, 4]. We identified 96 NAC genes from cassava and carried out detailed studies of their phylogeny, conserved motifs, gene structure, expression profiles in various tissues, and response to drought, osmotic, salt cold stresses and signaling of ABA and H2O2.
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