Original information
Original link:
http://doi.org/10.1111/nph.20175
Outline of Research
A recent study by Qi Xiaoquan's research team from the Institute of Botany, Chinese Academy of Sciences, published in New Phytologist, found that the ancestral genes of the genus Osa, OSC3 and OSC9, encode lupine alcohol synthase and gramina felin alcohol synthase, respectively. OsOSC10 encodes the enzyme xyloxyplugone synthase, which catalyzes the formation of the substrate 2,3-oxidoxysqualene to xylemberone. The expression of OsOSC10 gene was closely related to the grain size of rice, which was another triterpene cyclase with important biological functions found in rice after gram felmet alcohol synthase. This study provides new insights into the biological function and product diversity of the Osais OSC family.
Background:
2,3-氧化鲨烯环化酶(OSCs)是三萜类化合物合成途径中的关键酶。 在水稻粳稻品种中花11基因组中共有12个OSCs基因(OsOSC1-OsOSC12)。 漆小泉研究团队的前期研究揭示,OsOSC6的催化产物为β-amyrin和α-amyrin(Sun et al., 2013);粳稻品种中OsOSC7(OsOSC7j)的催化产物为帕克醇;而籼稻品种中OsOSC7(OsOSC7i)的催化产物为籼稻醇(Xue et al., 2018a);OsOSC11的催化产物为异乔木萜醇(Xue et al., 2012);OsOSC12基因编码禾谷绒毡醇合酶,该基因在水稻花粉发育中发挥着重要的作用(Xue et al., 2018b)。 然而,迄今为止,关于OsOSC1、OsOSC3、OsOSC4、OsOSC9和OsOSC10的具体功能尚属未知。
Findings:
1 OSC gene annotation in the genus Oryza
The rice variety Nakahua 11 (Oryza sativa L. ssp. japonica cv. Zhonghua11, ZH11) was used as the bait sequence, and the candidate OSC gene sequences in 63 rice varieties were obtained by genome-wide alignment. Then, 723 OSC gene sequences were successfully identified by manual annotation. Collineearity analysis showed that OSC1-OSC4 were located on chromosome 2 of rice. OSC7-OSC11 were located on chromosome 11 of rice. In most rice varieties, OSC6 is located on chromosome 6, while in N22, African cultivated rice (O. glaberrima), O. glumipatula, O. glaberrima, O. glumipatula. longistaminata) and southern wild rice (O. longistaminata) and southern wild rice. meridionalis), one copy is on chromosome 6 and the other is on chromosome 5 (Figure 1). In addition, with the exception of O. Except for the inversion of the collinearity of OSC12 in brachyantha, the arrangement of other OSC genes in the collinearity interval was basically the same (Fig. 1), indicating that the number and position of OSC genes were relatively conserved during the evolution of the genus Oryza, and there was no significant rearrangement or loss.
Fig.1 Collinear analysis of OSC gene in rice genus
2 OSC1、OSC3、OSC4、OSC9和OSC10催化功能分析
In order to explore the catalytic function of OSC1, OSC3, OSC4 and OSC9, representative gene sequences were selected from rice varieties with complete gene coding sequences for synthesis. Heterologous expression analysis of yeast showed that OSC1, 3, 4 and 9 could not use 2,3-oxidized squalene as substrate to form triterpene backbone compounds. Since these genes have complete coding sequences in the selected rice varieties, but their encoded proteins cannot catalyze the generation of triterpene scaffold compounds from 2,3-oxidized squalene, it is speculated that the function of these genes may have been lost during the evolution of rice, so the researchers reconstructed the ancestral sequences of the related genes and found that the ancestral genes of OSC3 and OSC9 encoded lupine alcohol synthase and graminated felin alcohol synthase, respectively (Fig. 2 a-d). In addition, by expressing the OsOSC10 gene in yeast, it was found that the catalytic product of OsOSC10 was xyloxyplugone (Fig. 2 e&f).
图2 ancOSC3、ancOSC9和OsOSC10催化功能分析
3 Evolutionary analysis of OSC genes in Oryza
The OSC gene in Oryza was clustered into three main branches: Oryza OSC12 and the OSC gene of dicots were clustered into one branch; Oryza OSC3, OSC4, OSC6, OSC8, OSC9, OSC10 and OSC11 are clustered into a single branch; Oryza OSC1, OSC2, and OSC7 are clustered into another branch. Further analysis showed that Oryza OSC2 originated from Pl02g02760 in Pharus latifolius. Oryza OSC8 originated from Pl06g02320 in the protograss plant Pharus latifolius; Oryza OSC3, OSC4 and OSC11 originated from Pl02g02770 in Pharus latifolius; Oryza OSC12 originates from Pl08g16820 in the protograss genus Pharus latifolius (Figure 3). For Oryza OSC1, OSC6, OSC7, OSC9 and OSC10, although the corresponding OSC gene was not found in Pharus latifolius, a grass-based basal crop, it was found in T. latifolius. urartu and S. Homologous genes of these genes were present in bicolor (Figure 3), suggesting that Oryza OSC1, OSC6, OSC7, OSC9, and OSC10 may have been produced during the evolution of grasses through gene replication events or other evolutionary processes.
Fig.3 Evolutionary analysis of OSC genes in Oryza
4 Biological function of OsOSC10 gene
OsOSC10 was mainly expressed in rice grains (Fig. 4a). Compared with the wild-type material, the expression level of OsOSC10 gene in the transgenic material was significantly changed. GC-MS was used to detect the content of xyloxylerone in the bark of each transgenic material, and it was found that compared with the wild type, the content of xyloxyleone in the grain bark of the mutant material was significantly reduced. However, the content of xyloxylerone in the grain bark of the overexpression material was significantly increased (Fig. 4 b&c), which indicated that OsOSC10 may affect the grain development process of rice.
Phenotypic analysis of transgenic materials showed that the grain width of OsOSC10 overexpressing material increased significantly, while that of mutant material decreased significantly (Fig. 4 d&e). Scanning electron microscopy (SEM) analysis showed that the number of cells in the OsOSC10 overexpressing material was significantly increased, while the number of cells in the mutant material was decreased (Fig. 4 f&g). Transcriptome analysis showed that the expression levels of multiple lipid transporters were significantly increased in the overexpression materials (Fig. 4 h), indicating that OsOSC10 may affect the accumulation of storage materials in the glume shell by regulating the expression of lipid transporter-related genes, thereby affecting the cell proliferation process and ultimately affecting the size of rice grains (Fig. 4 i).
Fig.4 Mechanism of OsOSC10 affecting grain size in rice
conclusion
In this study, the catalytic products of OSC3 and OSC9 ancestral genes in the genus Oryzae were successfully identified by reconstructing the ancestral sequences of OSC genes, respectively. The catalytic product of the OsOSC10 gene is xylembolone, which is involved in grain development in rice (Fig. 5). The results of this study open up a new perspective for in-depth exploration of the biological function and product diversity of Osais genes.
Fig.5 OSC genes and their functions in oryzae
Journal Introduction
New Phytologist is an internationally renowned journal focused on publishing outstanding original research in plant science and its applications. The journal is published by the New Phytologist Foundation and is currently edited by Alistair M. Hetherington. It was founded in 1902 and is currently published as a semi-monthly publication. The journal covers a wide range of topics, from intracellular processes to global environmental change, and can be divided into physiology and development, environment, evolution, and transformative plant biotechnology. The latest impact factor of the journal is 8.3, the 5-year average impact factor is 10.2, and the JCI citation index is 2.13, which is classified as a top journal in Q1 in the field of plant science.
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