A review for molecular biology of Morella rubra

Abstract：Red bayberry（Morella rubra）, is an economically important, subtropical evergreen fruit tree in southern China. The fruit has bright color and high nutritional value which make it popular with the domestic and foreign consumers. The fruit is not only eaten fresh, dried and canned, but is also widely used for making wine and juice. With the development of red bayberry market, more and more problems have emerged. Firstly, the breeding cycle of red bayberry is long, and the breeding method mainly depends on the natural variation and bud mutation. Secondly, red bayberry is not strongly resistant and is easily affected by environmental factors. For example, too much rain in early spring will affect pollen dispersal and reduce the fruit-setting rate. In addition, red bayberry are not covered by the exocarp, and the edible part is soft and easy to be damaged by machinery. Storage and transportation of the fruit after harvest are also unfavorable factors in the production and industrial development of red bayberry. The above problems will seriously inhibit the future development of the red bayberry industry. These problems are closely related to the genetic characteristics of red bayberry. Therefore, it is significant that explore the inherent determinants of the genetic characteristics of red bayberry. The old process of red bayberry breeding was slow and the cycle was long. The genomes are fundamental to molecular biology, genetics and breeding research on Morella species. The completion of red bayberry genome sequencing marks the shift from phenotypic studies to genotype studies, from single-gene studies to genome-wide association analysis. This paper reviews the following three aspects in red bayberry molecular biology: 1. The genetic diversity research progress of red bayberry. DNA molecular marker is a comparatively ideal genetic markers developed after the shape marker, cellular marker and biochemical marker. Alarge number of previous studies about DNA molecular marker in bayberry have provided reliable auxiliary materials for the genetic breeding and molecular research of red bayberry and laid a foundation for the follow-up research. 2. The genome research progress of red bayberry. The publication of the whole genome sequencing results of red bayberry will help us to understand the structure and function of red bayberry, which is a great guiding significance to explore the origin and evolution of red bayberry, clone the important functional genes, and accelerate the process of molecular breeding. At the same time, the genome sequence of red bayberry can be used as a reference for other Myricaceae plants’genome sequencing (The Myricaceae is a small, sub-cosmopolitan family of about 50 species) to accelerate the process of genetic breeding of other plants. 3. The sex differentiation mechanism of red bayberry. In order to explain the phenomenon of male flowers in the female trees of red bayberry and find the genes that determine the sexual differentiation of bayberry, Jia combined with the whole genome sequencing information of red bayberry, sequenced the two mixing pools of 100 female red bayberry and 100 male red bayberry, and resequenced the three female and three male red bayberry respectively, and found that: there is a Female specific region (FSR) with a length of about 59 kb on chromosome (No.8) of red bayberry. It is deduced that the sex determination mechanism of red bayberry is Z/W type. FSR segment contained seven predicted genes, four gene (MrASP2, MrCPS2, MrSAUR2 and MrFT2) in FSR segment were associated with sexual determination. The researchers believe that the expression level of FSR region gene determines the final direction of sex differentiation of red bayberry. When the gene expression level of FSR region is induced by environmental factors, male flowers of female red bayberry will appear. This study reveals the genetic basis of sex determination of red bayberry and is helpful to the further development of genetic breeding of red bayberry. Finally, we prospected the future development direction of molecular biology research. Future red bayberry molecular biology research mainly revolves around the following aspects：firstly, making full use of the rich information resources of genome-wide of red bayberry, developing and applying new experimental methods, analyzing all the gene function of red bayberry genome at the genome or system level comprehensively, studying the gene expression and its regulation mode to reveal the growth, environmental response interaction molecular network, metabolism and other molecular mechanisms of red bayberry. The gene expression and its regulation pattern were studied to reveal the molecular mechanism of red bayberry growth, development, the environmental response, interaction molecular network and metabolism and so on. Secondly, in the actual production, the red bayberry resistance is poor, so producing with excellent properties such as cold resistance, drought resistance to meet the needs of production is urgent. Therefore, it will also be one of the research directions in the related research fields to study the physiological mechanism of red bayberry under stress, explore anti-stress genes, and obtain transgenic red bayberry with promotion prospects. This could provide new materials for the cultivation, processing and development of medical care products of red bayberry.This study was aimed at providing more scientific references for the breeding and exploitation of red bayberry.