Involvement of three ABRE-binding factors in the gametophytic self-incompatibility reaction in pear

Abstract

Self-incompatibility (SI) facilitates the rejection of pollen by self S-RNase. It is believed that a large number of genes are responsive to SI reactions; however, little is known about the transcriptional regulation of these genes. Herein, we explored the role of ABRE-binding factor (ABF) in gametophytic self-incompatibility (GSI). Phylogenetic analysis showed that eight ABF genes in pear clustered with five ABF genes in Arabidopsis. Of these ABF genes, PbABF.E.1 and PbABF.E.2 were expressed in all tissues, and PbABF.B was expressed in most tissues. These three ABF genes were also detected in the self- and cross-pollinated styles. Additionally, RNA-Seq analysis revealed 11,476 genes that were differentially expressed between the self- and cross-pollinated styles at 24, 48, and/or 72 h after pollination. Of these differentially expressed genes (DEGs), 278 were differentially expressed between the self- and cross-pollinated styles at any stage and thus are responsive to the GSI reaction. Notably, abscisic acid-responsive elements were detected in the promoter sequences of the 1213 DEGs including the six genes negatively correlated with pollen tube growth. The dual-luciferase assay showed that the promoter of these six genes was activated by PbABF.B, PbABF.E.1, and/or PbABF.E.2. Therefore, PbABF.B, PbABF.E.1, and PbABF.E.2 were involved in the GSI reaction by mediating the expression of genes responsive to the GSI reaction.