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Molecular Mechanism of Plant Color Change
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Alterations in certain biochemical components may lead to significant changes in yield or quality of many animals and plants which are used as human food and medical resources. With the advance of modern biology, it has become a new trend to explore the regularity of productivities of metabolic pathways and their influencing factors. As water-soluble pigments produced broadly by plants, anthocyanins have been favorably taken as part of both food and medicine. However, research about molecular regulation of the anthocyanin pathway was still at its infancy until a recent breakthrough. A research group (led by Dr. Yingqing Lu) from the Institute of Botany, Chinese Academy of Sciences, has focused on the transcriptional regulation of the anthocyanin pathway for several years. Researchers of the group lately found that two (MYB, bHLH) of the three transcriptional factors (TFs) could bind at specific sites to the 5' DNA of the target genes; the spatial orientations of the binding sites and the interactions between the TF proteins largely controlled the expression levels of the enzymes involved in anthocyanin synthesis. They showed that the regulatory mechanism by the three regulators was much the same across angiosperms, and there was little evidence supporting separate regulatory mechanisms for the same metabolic pathway. Being part of the flavonoid metabolic network, the proanthocyanin pathway was shown to be regulated also as one unit, similar to the case of the anthocyanin pathway.

This progress was achieved owning to applications of multidisciplinary approaches and detailed mutation analysis. The researchers adopted bioinformatic approaches to first propose the hypothesis for the binding sites (cis elements). Carefully designed point mutations were then tested via in vitro analysis and in vivo experiments. The fine structure of the cis elements were gradually revealed through recurrent tests in multiple experiments. By analyzing the real-time expression levels of the enzymes and their regulators in the common morning glory and testing other known anthocyanin genes across angiosperms, the researchers found the structures for the cis elements recognized by anthocyanin MYB and bHLH as ANCNNCC and CACN (A/C/T) (G/T), respectively. They suggest that a metabolic network can be regulated by different transcriptional factors in different tissues, and the mere interaction between transcription factors and cis elements can be key to the variation of metabolites.

This breakthrough shed some light on the regulatory mechanisms concerning MYB and bHLH, which belong to the largest transcriptional factor families in plants, respectively. In the past, not only the extreme variation of the cis elements in the promoter regions of the enzymes was difficult to analyze, but also the highly redundant regulation by multiple transcriptional factors on the common target genes had led to wrong conclusions. These issues were well solved in the new study. Since the combinational regulation formed by MYB, bHLH, and WDR also exists in several other biological processes, the new advance will promote future research in regulations of these biological systems.

The new results have been published in Journal of Experimental Botany (66 (13): 3775-3789). The work was supported by funds from the National Natural Science Foundation of China (91331116, 31070263) and Chinese Academy of Sciences (KSCX2-YW-N-043).

Article link:

http://jxb.oxfordjournals.org/content/66/13/3775.full.pdf.html

 

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