EjAP2-1, anAP2/ERFgene, is a novel regulator of fruit lignification induced by chilling injury, via interaction withEjMYBtranscription factors

Summary Lignin biosynthesis is regulated by many transcription factors, such as those of the MYB and NAC families. However, the roles of AP 2/ ERF transcription factors in lignin biosynthesis have been rarely investigated. Eighteen Ej AP 2/ ERF genes were isolated from loquat fruit ( Eriobotrya japonica ), which undergoes postharvest lignification during low temperature storage. Among these, expression of Ej AP 2‐1 , a transcriptional repressor, was negatively correlated with fruit lignification. The dual‐luciferase assay indicated that Ej AP 2‐1 could trans‐repress activities of promoters of lignin biosynthesis genes from both Arabidopsis and loquat. However, Ej AP 2‐1 did not interact with the target promoters ( Ej4 CL 1 ). Yeast two‐hybrid (Y2H) and bimolecular fluorescence complementation (Bi FC ) assays indicated protein–protein interactions between Ej AP 2‐1 and lignin biosynthesis‐related Ej MYB 1 and Ej MYB 2. Furthermore, repression effects on the Ej4 CL 1 promoter were observed with the combination of Ej AP 2‐1 and Ej MYB 1 or Ej MYB 2, while Ej AP 2‐1 with the EAR motif mutated ( mEjAP 2‐1) lost such repression, although mEjAP 2‐1 still interacted with Ej MYB protein. Based on these results, it is proposed that Ej AP 2‐1 is an indirect transcriptional repressor on lignin biosynthesis, and the repression effects were manifested by EAR motifs and were conducted via protein–protein interaction with EjMYBs.