APETALA2/ethylene response factor (AP2/ERF) transcription factor (TF) is a superfamily in plant kingdom, which has been reported to be involved in regulation of plant growth and development, fruit ripening, defense response, and metabolism. As the final response gene in ethylene signaling pathway, AP2/ERF TF could feedback modulate phytohormone biosynthesis, including ethylene, cytokinin, gibberellin, and abscisic acid. Moreover, AP2/ERF TF also participates in response to the signals of auxin, cytokinin, abscisic acid, and jasmonate. Thus, this superfamily is key regulator for connecting the phytohormonal signals. In this review, based on the evidence of structural and functional studies, we discussed the multiple regulator roles of AP2/ERF TF in angiosperm, and then constructed the network model of AP2/ERF TF in response to various phytohormonal signals and regulatory mechanism of the cross-talk.

Peach is a typical climacteric fruit that releases ethylene during fruit ripening. Several studies have been conducted on the transcriptional regulation of ethylene biosynthesis in peach fruit. Herein, an ethylene response factor, PpERF.A16, which was induced by exogenous ethylene, could enhance ethylene biosynthesis by directly inducing the expression of1-aminocyclopropane-1-carboxylic acid synthase(PpACS1) and1-aminocyclopropane-1-carboxylic acid oxidase(PpACO1) genes. Moreover, the NAM/ATAF1/2/CUC2 (NAC) transcription factor (TF)PpNAC.A59was coexpressed withPpERF.A16in all tested peach cultivars. Interestingly, PpNAC.A59 can directly interact with the promoter ofPpERF.A16to induce its expression but not enhanceLUCactivity driven by any promoter ofPpACS1orPpACO1. Thus, PpNAC.A59 can indirectly mediate ethylene biosynthesis via the NAC-ERF signaling cascade to induce the expression of bothPpACS1andPpACO1. These results enrich the genetic network of fruit ripening in peach and provide new insight into the ripening mechanism of other perennial fruits.

Self-incompatibility (SI) is a widespread genetically determined system in flowering plants that prevents self-fertilization to promote gene flow and limit inbreeding. S-RNase-based SI is characterized by the arrest of pollen tube growth through the pistil. Arrested pollen tubes show disrupted polarized growth and swollen tips, but the underlying molecular mechanism is largely unknown. Here, we demonstrate that the swelling at the tips of incompatible pollen tubes in pear (Pyrus bretschneideri, Pbr) is mediated by the SI-induced acetylation of the soluble inorganic pyrophosphatase (PPA). PbrPPA5. Acetylation at Lys-42 of PbrPPA5 by the acetyltransferase GCN5-related N-acetyltransferase 1 (GNAT1) drives accumulation of PbrPPA5 in the nucleus, where it binds to the transcription factor PbrbZIP77, forming a transcriptional repression complex that inhibits the expression of the pectin methylesterase (PME) gene PbrPME44. The function of PbrPPA5 as a transcriptional repressor does not require its pyrophosphatase activity. Downregulating PbrPME44 resulted in increased levels of methyl esterified pectins in growing pollen tubes, leading to swelling at their tips. These observations suggest a mechanism for PbrPPA5-driven swelling at the tips of pollen tubes during the SI response. The targets of PbrPPA5 include genes encoding cell wall-modifying enzymes, which are essential for building a continuous sustainable mechanical structure for pollen tube growth.

Background: Pear fruit exhibit a single sigmoid pattern during development, while peach and strawberry fruits exhibit a double sigmoid pattern. However, little is known about the differences between these two patterns. Results: In this study, fruit weights were measured and paraffin sections were made from fruitlet to maturated pear, peach, and strawberry samples. Results revealed that both single and double sigmoid patterns resulted from cell expansion, but not cell division. Comparative transcriptome analyses were conducted among pear, peach, and strawberry fruits at five fruit enlargement stages. Comparing the genes involved in these intervals among peaches and strawberries, 836 genes were found to be associated with all three fruit enlargement stages in pears (Model I). Of these genes, 25 were located within the quantitative trait locus (QTL) regions related to fruit weight and 90 were involved in cell development. Moreover, 649 genes were associated with the middle enlargement stage, but not early or late enlargement in pears (Model II). Additionally, 22 genes were located within the QTL regions related to fruit weight and 63 were involved in cell development. Lastly, dual-luciferase assays revealed that the screened bHLH transcription factors induced the expression of cell expansion-related genes, suggesting that the two models explain the single sigmoid pattern. Conclusions: Single sigmoid patterns are coordinately mediated by Models I and II, thus, a potential gene regulation network for the single sigmoid pattern was proposed. These results enhance our understanding of the molecular regulation of fruit size in Rosaceae.