The NF-Y Transcription Factor Family in Watermelon: Re-Characterization, Assembly of ClNF-Y Complexes, Hormone- and Pathogen-Inducible Expression and Putative Functions in Disease Resistance.

Nuclear factor Y (NF-Y) is a heterotrimeric transcription factor that binds to the CCAAT -element in the promoters of target genes and plays critical roles in plant growth, development, and stress responses. In the present study, we aimed to re-characterize the family in watermelon, examine the assembly of ClNF-Y complexes, and explore their possible involvement in disease resistance. A total of 25 genes (7 , 10 , and 8 ) were identified in the watermelon genome. The family was comprehensively characterized in terms of gene and protein structures, phylogenetic relationships, and evolution events. Different types of -elements responsible for plant growth and development, phytohormones, and/or stress responses were identified in the promoters of the genes. ClNF-YAs and ClNF-YCs were mainly localized in the nucleus, while most of the ClNF-YBs were localized in the cytoplasm of cells. ClNF-YB5, -YB6, -YB7, -YB8, -YB9, and -YB10 interacted with ClNF-YC2, -YC3, -YC4, -YC5, -YC6, -YC7, and -YC8, while ClNF-YB1 and -YB3 interacted with ClNF-YC1. A total of 37 putative ClNF-Y complexes were identified, e.g., ClNF-YA1, -YA2, -YA3, and -YA7 assembled into 13, 8, 8, and 8 ClNF-Y complexes with different ClNF-YB/-YC heterodimers. Most of the genes responded with distinct expression patterns to defense hormones such as salicylic acid, methyl jasmonate, abscisic acid, and ethylene precursor 1-aminocyclopropane-1-carboxylate, and to infection by the vascular infecting fungus f. sp. . Overexpression of , , , , and in transgenic Arabidopsis resulted in an earlier flowering phenotype. Overexpression of in Arabidopsis led to enhanced resistance while overexpression of and resulted in decreased resistance against . Similarly, overexpression of , , and strengthened resistance while overexpression of and attenuated resistance against pv. DC3000. The re-characterization of the family provides a basis from which to investigate the biological functions of genes in respect of growth, development, and stress response in watermelon, and the identification of the functions of some genes in disease resistance enables further exploration of the molecular mechanism of in the regulation of watermelon immunity against diverse pathogens.