Promoter cloning and activities analysis of JmLFY, a key gene for flowering in Juglans mandshurica

Abstract

Juglans mandshurica (Manchurian walnut) is a precious timber and woody grain and oil species in Northeast China. The heterodichogamous characteristic phenomenon resulted in the non-synchronous flowering and development of male and female flowers, which limited the mating and the yield and quality of fruits. LFY is a core gene in the flowering regulatory networks, which has been cloned in J. mandshurica, and the function has also been verified preliminarily. In this study, the JmLFY promoter sequence with different lengths of 5′-deletion (pLFY1-pLFY6) were cloned and conducted bioinformatics analysis, the promoter activities were analyzed by detecting their driving activity to GUS gene in the tobacco plants that transformed with different promoter sequence stably or transiently. After that, the interaction between JmSOC1 and JmLFY gene promoter was also analyzed via yeast single-hybrid. The results showed that the promoter sequence contains core cis-acting elements essential for eukaryotic promoters, hormone response elements, defense- and stress-responsive elements, flowering-related elements, etc. Transgenic tobacco plants with pLFY1 were obtained by Agrobacterium infection using the pCAMBIA1301 expression vector, and the GUS gene driven by the JmLFY promoter was detected to express in the leaf, stem, flower, and root of the transformed tobacco plant, which indicated that the obtained JmLFY promoter had driving activity. GUS histochemical staining and enzyme activity detection showed that promoter fragments with different lengths had promoter activity and could respond to the induction of long photoperiod, low temperature, salicylic acid (SA), IAA, GA3, and methyl jasmonate (MeJA). The core regulatory region of JmLFY gene promoter in J. mandshurica was between −657 bp and −1,904 bp. Point-to-point validation of yeast single-hybrid confirmed the interaction between JmSOC1 and JmLFY gene promoter, which indicated that JmLFY gene is the downstream target of JmSOC1. These results reveal relevant factors affecting JmLFY gene expression and clarify the molecular mechanism of JmLFY gene regulation in the flower developmental partially, which will provide a theoretical basis for regulating the flowering time by regulating JmLFY gene expression in J. mandshurica.