Date Published: March 6, 2019
Publisher: Public Library of Science
Author(s): Claire Guérin, Jane Roche, Vincent Allard, Catherine Ravel, Said Mouzeyar, Mohamed Fouad Bouzidi, Maoteng Li.
The NAC family is one of the largest plant-specific transcription factor families, and some of its members are known to play major roles in plant development and response to biotic and abiotic stresses. Here, we inventoried 488 NAC members in bread wheat (Triticum aestivum). Using the recent release of the wheat genome (IWGS RefSeq v1.0), we studied duplication events focusing on genomic regions from 4B-4D-5A chromosomes as an example of the family expansion and neofunctionalization of TaNAC members. Differentially expressed TaNAC genes in organs and in response to abiotic stresses were identified using publicly available RNAseq data. Expression profiling of 23 selected candidate TaNAC genes was studied in leaf and grain from two bread wheat genotypes at two developmental stages in field drought conditions and revealed insights into their specific and/or overlapping expression patterns. This study showed that, of the 23 TaNAC genes, seven have a leaf-specific expression and five have a grain-specific expression. In addition, the grain-specific genes profiles in response to drought depend on the genotype. These genes may be considered as potential candidates for further functional validation and could present an interest for crop improvement programs in response to climate change. Globally, the present study provides new insights into evolution, divergence and functional analysis of NAC gene family in bread wheat.
As sessile organisms, plants have developed diverse strategies to modulate their development and growth according to environmental signals such as day/night alternation or daily temperature variations . At the molecular and cellular levels, the early mechanisms of response to these stimuli include signal perception by receptors, followed by signalling cascades involving changes in membrane permeability, protein phosphorylations by protein kinases or regulations of the target protein expression by transcription factors (TFs) . About 6–8% of the plant genome is allocated to the coding of more than 1,500 TFs  of which 45% belong to plant-specific families . Among more than 80 TF families, AP2/EREBP, bZIP, MYB/MYC, NAC and WRKY families are known to be strongly involved in the response to biotic or abiotic stresses in plants [5–16]. The NAC (NAM (No Apical Meristem)–ATAF (Arabidopsis Transcription Activation Factor)–CUC (Cup-shaped Cotyledons)) family is one of the largest groups of plant specific TFs, and has been described in several plant species. In the model plants, Arabidopsis and rice, this family includes 117 and 151 members, respectively . NAC family members have also been reported in Brachypodium distachyon (118 members) , soybean (101 genes) , maize (157 members) , durum wheat (168 members) , and more recently in Fragaria × ananassa fruits (112 members) .
The sequence availability of the whole bread wheat genome and expression data among different wheat genotypes, organs, and conditions are rich resources for systematic analysis of gene transcriptional regulation. Particularly, these data provide useful information for the identification of candidate genes involved in wheat development and its stress response.
In conclusion, we performed a comprehensive study of NAC TFs in the bread wheat genome (T. aestivum), cultivar Chinese Spring. We identified a high quality set of 361 TaNAC genes in common with those described in Borrill et al. . We provided evidences as to how small scale duplications and retroposition contributed to the expansion of this family of genes. Finally, the expression patterns of 23 TaNAC genes in two organs at two stages under drought in the field, combined with our study of duplication events, revealed a functional diversification of this gene family’s members. Further functional characterizations of five grain specific TaNAC genes are in process to identify their role in the wheat grain development and in abiotic stress responses.