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The nascent polypeptide-associated (NAC) complex was described in yeast as a heterodimer composed of two subunits, &#945; and &#946;, and was shown to bind to the nascent polypeptides newly emerging from the ribosomes. NAC function was widely described in yeast and several information are also available about its role in plants. The knock down of individual NAC subunit(s) led usually to a higher sensitivity to stress. In <i>Arabidopsis thaliana</i> genome, there are five genes encoding NAC&#945; subunit, and two genes encoding NAC&#946;. Double homozygous mutant in both genes coding for NAC&#946; was acquired, which showed a delayed development compared to the wild type, had abnormal number of flower organs, shorter siliques and greatly reduced seed set. Both <i>NAC&#946;</i> genes were characterized in more detail&#8212;the phenotype of the double homozygous mutant was complemented by a functional NAC&#946; copy. Then, both <i>NAC&#946;</i> genes were localized to nuclei and cytoplasm and their promoters were active in many organs (leaves, cauline leaves, flowers, pollen grains, and siliques together with seeds). Since flowers were the most affected organs by <i>nac&#946;</i> mutation, the flower buds&#8217; transcriptome was identified by RNA sequencing, and their proteome by gel-free approach. The differential expression analyses of transcriptomic and proteomic datasets suggest the involvement of NAC&#946; subunits in stress responses, male gametophyte development, and photosynthesis.