Bioscience Methods 2024, Vol.15, No.6, 289-301 http://bioscipublisher.com/index.php/bm 292 cis-polyisoprene. The interplay between the MVA and MEP pathways in H. brasiliensis highlights the complexity of isoprenoid biosynthesis and its regulation (Chuntai et al., 2017). Subcellular compartmentalization plays a significant role in the biosynthesis of rubber in H. brasiliensis. The separation of the MVA pathway in the cytosol and the MEP pathway in the plastids allows for the distinct regulation and coordination of isoprenoid biosynthesis. This compartmentalization ensures the efficient production of IPP and DMAPP, which are essential for the synthesis of cis-polyisoprene. Additionally, the expression of FPS genes in different tissues and their regulation by environmental factors further influence rubber biosynthesis in H. brasiliensis (Chuntai et al., 2017). By understanding the biochemical pathways and the role of key enzymes in rubber biosynthesis, researchers can develop strategies to enhance rubber production in bothEucommia ulmoides andHevea brasiliensis. 4 Molecular Regulation of Rubber Biosynthesis 4.1 Gene expression and regulation inEucommia ulmoides Eucommia ulmoides exhibits high expression levels of multiple genes involved in stress responses and the biosynthesis of secondary metabolites, which may contribute to its significant environmental adaptability. This includes the expansion of gene families related to farnesyl diphosphate synthases (FPSs) and rubber elongation factors, which are crucial for the biosynthesis of trans-polyisoprene, the primary component of Eu-rubber (Wuyun et al., 2017) (Figure 1). Additionally, the NAC transcription factor family in E. ulmoides, which is involved in various stress responses and secondary metabolite synthesis, shows differential expression across various tissues, indicating their potential role in rubber biosynthesis (Zhang et al., 2023). Several key transcription factors (TFs) involved in regulating the metabolism of Brazilian CPI have been identified, including WRKY, MADS, NAC, and MYB. These TFs regulate the expression of synthase genes related to natural rubber biosynthesis (Wang et al., 2013; Li et al., 2016; Cao et al., 2017; Wang et al., 2017). The expression of EuFPS1 in Eucommia is transcriptionally activated by EuWRKY30, and overexpression of EuWRKY30 significantly increases the expression level of EuFPS1, thereby promoting the biosynthesis of TPI (Zhang et al., 2024). In E. ulmoides, enzymes involved in the chlorogenic acid biosynthesis pathway are preferentially expressed in the leaves rather than in the bark. This suggests a tissue-specific regulation of secondary metabolite biosynthesis, which may be linked to the plant's overall metabolic strategy and adaptation mechanisms (Li et al., 2020). 4.2 Gene expression and regulation inHevea brasiliensis In Hevea brasiliensis, long noncoding RNAs (lncRNAs) and microRNAs exhibit differential expression across various clones, indicating their regulatory roles in rubber biosynthesis. These noncoding RNAs are involved in complex regulatory networks that control the expression of genes associated with latex production and stress responses (Liu et al., 2018). Hevea brasiliensis has undergone an expansion of genes related to rubber biosynthesis, particularly those encoding rubber particle membrane proteins (RPMPs) such as rubber elongation factor (REF) and small rubber particle protein (SRPP). These genes are highly expressed in latex, underscoring their critical role in the production of cis-polyisoprene, the main component of natural rubber (Chow et al., 2007). Additionally, farnesyl pyrophosphate synthase (FPS) genes in H. brasiliensis are highly expressed in latex and are upregulated in response to tapping and hormonal treatments, further highlighting their importance in rubber biosynthesis (Chuntai et al., 2017). The transcription profiles of rubber biosynthesis-related genes in H. brasiliensis are highly tissue-specific. For instance, the TGA transcription factors, particularly HbTGA1, regulate the expression of multiple rubber biosynthesis genes in latex. These transcription factors bind to the promoters of key biosynthetic genes and modulate their activity in response to stress signals such as jasmonate and salicylic acid, indicating a sophisticated level of transcriptional regulation (Guo et al., 2022). This tissue-specific and alternative transcriptional regulation ensures the efficient production of natural rubber in the appropriate cellular context.
RkJQdWJsaXNoZXIy MjQ4ODYzNA==