Cis-regulated additively expressed genes play a fundamental role in the formation of triploid loquat (Eriobotrya japonica (Thunb.) Lindl.) Heterosis

Advances in Research on the Mechanism of Heterosis in Plants

Heterosis is a common biological phenomenon in nature. It substantially contributes to the biomass yield and grain yield of plants. Moreover, this phenomenon results in high economic returns in agricultural production. However, the utilization of heterosis far exceeds the level of theoretical research on this phenomenon. In this review, the recent progress in research on heterosis in plants was reviewed from the aspects of classical genetics, parental genetic distance, quantitative trait loci, transcriptomes, proteomes, epigenetics (DNA methylation, histone modification, and small RNA), and hormone regulation. A regulatory network of various heterosis-related genes under the action of different regulatory factors was summarized. This review lays a foundation for the in-depth study of the molecular and physiological aspects of this phenomenon to promote its effects on increasing the yield of agricultural production.

Genotyping of polyploid plants using quantitative PCR: application in the breeding of white-fleshed triploid loquats (Eriobotrya japonica)

BACKGROUND

Ploidy manipulation is effective in seedless loquat breeding, in which flesh color is a key agronomic and economic trait. Few techniques are currently available for detecting the genotypes of polyploids in plants, but this ability is essential for most genetic research and molecular breeding.

RESULTS

We developed a system for genotyping by quantitative PCR (qPCR) that allowed flesh color genotyping in multiple tetraploid and triploid loquat varieties (lines). The analysis of 13 different ratios of DNA mixtures between two homozygous diploids (AA and aa) showed that the proportion of allele A has a high correlation (R² = 0.9992) with parameter b [b = a₁/(a₁ + a₂)], which is derived from the two normalized allele signals (a₁ and a₂) provided by qPCR. Cluster analysis and variance analysis from simulating triploid and tetraploid hybrids provided completely correct allelic configurations. Four genotypes (AAA, AAa, Aaa, aaa) were found in triploid loquats, and four (AAAA, AAAa, AAaa, Aaaa; absence of aaaa homozygotes) were found in tetraploid loquats. DNA markers analysis showed that the segregation of flesh color in all F₁ hybrids conformed to Mendel's law. When tetraploid B431 was the female parent, more white-fleshed triploids occurred among the progeny.

CONCLUSIONS

qPCR can detect the flesh color genotypes of loquat polyploids and provides an alternative method for analyzing polyploid genotype and breeding, dose effects and allele-specific expression.

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

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.

Chromatin dynamics during interphase and cell division: similarities and differences between model and crop plants

Genetic information in the cell nucleus controls organismal development and responses to the environment, and finally ensures its own transmission to the next generations. To achieve so many different tasks, the genetic information is associated with structural and regulatory proteins, which orchestrate nuclear functions in time and space. Furthermore, plant life strategies require chromatin plasticity to allow a rapid adaptation to abiotic and biotic stresses. Here, we summarize current knowledge on the organization of plant chromatin and dynamics of chromosomes during interphase and mitotic and meiotic cell divisions for model and crop plants differing as to genome size, ploidy, and amount of genomic resources available. The existing data indicate that chromatin changes accompany most (if not all) cellular processes and that there are both shared and unique themes in the chromatin structure and global chromosome dynamics among species. Ongoing efforts to understand the molecular mechanisms involved in chromatin organization and remodeling have, together with the latest genome editing tools, potential to unlock crop genomes for innovative breeding strategies and improvements of various traits.