The gender of higher plants has been demonstrated in monoecious and androgyne (Oryza sativa and triticum), monoecious but androgyne (Zea mays and Ricinus communis), and dioecism plants (poplar and Cannabis sativa). Most of these higher plants are monoecious, since dioecism accounts for only 5% of the flowering higher plants (Lionakis, 1985). The evolutionary process initiated with monoecism and androgyne, evolved to monoecism but androgyne, and subsequently resulted in dioecism. In addition, flowers also evolved from bisexual to unisexual presentation (Durand and Durand, 1984; Irish and Nelson, 1989; Meng et al., 1995).
The chinese bayberry (Morella rubra, former name Myrica rubra) is a subtropical evergreen tree native to China and other Asian countries (Chen et al., 2004; Jia et al., 2015; Xie et al., 2011). Chinese bayberry is planted as an important fruit crop in China, and mainly cultivated in Zhejiang, Fujian, and Jiangsu provinces (Zhang et al., 2009). In 2015, the planting area for chinese bayberry consisted of ≈230,000 hm2 in China. Chinese bayberry (2n = 16) belongs to the Myricaceae family, is usually dioecious, and is wind pollinated (Erickson and Hamrick, 2003; González-Pérez et al., 2009; Stokes, 1997). In addition, only a few individuals are monoecious (Jiao et al., 2013), although this phenomenon is very rare. The male and female populations of chinese bayberry have similar genetic diversity in terms of the average number of alleles and level of heterozygosity, but were clearly separated by genetic structure analysis due to two markers associated with sex type (Jia et al., 2015). In our previous studies on the chinese bayberry, we found one monoecious mutant in ‘Fugong-1’. This mutant was stable for a few years across continuous generations in different locations (Lin et al., 2013, 2016). The gender-decision system of plants is complex and various, and is affected by sex chromosomes, sex determination genes, gene balance, and the environment (Delph, 2003). SRAP (sequence-related amplified polymorphism) identification showed that ‘Fugong-1’ was as close as 95.7% to its monoecious mutant based on genetic distance (Lin et al., 2013). However, which resulted in this phenomenon was not clear.
In recent years, transcriptome sequencing technology using RNA-seq, which is based on next-generation sequencing, has been widely used in a range of research fields and can provide a quick and convenient method to establish the basic platform of plant molecular studies without the need for corresponding sequenced genome information as a reference (Biao et al., 2015; Brautigam et al., 2011; Dubey et al., 2011; Merianne et al., 2014; Parchman et al., 2010; Shi et al., 2011; Wang et al., 2010; Wu et al., 2010). Feng et al. (2012) obtained 41,239 unigenes from three different ripened fruits by using RNA-seq. The authors also developed a visual network of genetic dynamic changes within the chinese bayberry during fruit development and during the ripening stages using interactive pathways analyses. Yang et al. (2015) revealed key insights into stamen and pistil development in wheat (Triticum aestivum L.) by identifying 206 DEGs that were highly correlated with their development. These genes included WM27B, DL, YAB1, YABBY4, WM5, CER1, and WBLH1, which had been previously implicated in flower development.
In this study, we used ‘Fugong-1’ chinese bayberry and its monoecious mutant inflorescence in three different developing stages as our targets and sequenced their transcriptome using RNA-seq technology. By using inflorescence transcriptomes at different developing stages in these varieties, we aimed to identify the genes related to gender development. This study also provides important data for further studies on the sex types of the chinese bayberry.
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