Functional Identification of EjGIF1 in Arabidopsis and Preliminary Analysis of Its Regulatory Mechanisms in the Formation of Triploid Loquat Leaf Heterosis.

Chao Liu,Lingli Wang,Guolu Liang,Renwei Huang

doi:10.3389/fpls.2020.612055

Abstract

Although several results have been obtained in triploid loquat heterosis (i.e., leaf size of triploid loquat) studies in the past years, the underlying mechanisms of the heterosis are still largely unknown, especially the regulation effects of one specific gene on the corresponding morphology heterosis. In this study, we sought to further illustrate the regulatory mechanisms of one specific gene on the leaf size heterosis of triploid loquats. A leaf size development-related gene (EjGIF1) and its promoter were successfully cloned. Ectopic expression of EjGIF1 in Arabidopsis showed that the leaf size of transgenic plantlets was larger than that of WTs, and the transgenic plantlets had more leaves than WTs. Quantitative Reverse Transcription PCR (qRT-PCR) showed that the expression level of EjGIF1 showed an AHP expression pattern in most of the hybrids, and this was consistent with our previous phenotype observations. Structure analysis of EjGIF1 promoter showed that there were significantly more light-responsive elements than other elements. To further ascertain the regulatory mechanisms of EjGIF1 on triploid loquat heterosis, the methylation levels of EjGIF1 promoter in different ploidy loquats were analyzed by using bisulfite sequencing. Surprisingly, the total methylation levels of EjGIF1 promoter in triploid showed a decreasing trend compared with the mid-parent value (MPV), and this was also consistent with the qRT-PCR results of EjGIF1. Taken together, our results suggested that EjGIF1 played an important role in promoting leaf size development of loquat, and demethylation of EjGIF1 promoter in triploid loquats caused EjGIF1 to exhibit over-dominance expression pattern and then further to promote leaf heterosis formation. In conclusion, EjGIF1 played an important role in the formation of triploid loquat leaf size heterosis.

Highlights

Heterosis, or hybrid vigor, is a common phenomenon in many diploid or polyploid organisms, which means the biomass, resistance ability, yield, and some other agronomic traits in hybrids are greater than that of the parents (Hofmann, 2012)
The same with the traditional taxonomy, our results showed that EjGIF1 was separated from the other GIF1 proteins clearly, and EjGIF1 was clustered into Rosaceae and was closest to Malus × domestica (Figure 1B)
Studies on leaf development are mainly focused on the model plants, grasses, or herbaceous plants, such as Arabidopsis, barley, Brassica napus etc., and there are relatively few studies on the leaf development of woody plants (Mizukami and Fischer, 2000; Osnato et al, 2010; Liu et al, 2012; Dkhar and Pareek, 2014)

Summary

Introduction

Hybrid vigor, is a common phenomenon in many diploid or polyploid organisms, which means the biomass, resistance ability, yield, and some other agronomic traits in hybrids are greater than that of the parents (Hofmann, 2012). Study on triploid loquat, Liu et al (2018a) analyzed the leaf transcriptomes of the triploid loquats and their parents in two cross combinations and identified that 94.56 and 86.97% transcripts were expressed additively in the two cross combinations, respectively, and only 5.44 and 13.03% genes expressed non-additively. These results indicated that additively expressed genes may play a fundamental role in the formation of triploid loquats

Methods

Results

Conclusion