Abstract: 【Objective】 Guzmania is a trendy flower. Its flower formation and bracts discoloration process are often accompanied by green fade. To analyze the reason which bract’s green fade, it is necessary to isolate key genes and explore molecular mechanism of chlorophyll biosynthesis and degradation metabolism in the process of bracts discoloration. 【Method】 By cDNA library construction and EST sequencing batch, two key enzyme genes in chlorophyll biosynthesis pathway, including glutamyl-tRNA synthetase (GTS) and Uroporphyrinogen-Ⅲ synthase (UROS), were obtained. By homology cloning technology, a key enzyme gene in chlorophyll degradation pathway, pheophytin pheophorbide hydrolase gene (PPH), was obtained. Through measuring chlorophyll content using light transmittance measurement method, flavonoid content using HPLC method and analyzing gene expression pattern of key genes in chlorophyll metabolism using real-time quantitative PCR method, the molecular mechanism which green fade in discoloration bracts was studied. 【Result】 GTS obtained has 1 140 bp (GenBank: KP144289) in cDNA sequence, which compiles a 171 amino acid protein sequence, and has GlnRS-cataytic core and Nt-trans superfamily conservative regions; UROS obtained has 613 bp (GenBank: KP144288) in cDNA sequence, which compiles a 188 amino acid protein sequence, and has HemD and HemD Superfamily conservative regions; PPH obtained has 266 bp (GenBank: KP723523) in cDNA sequence, which compiles a 88 amino acid protein sequence, and has Abhydrolase-6 conservative region. Through measuring chlorophyll, flavonoid content and studying the expression level of key genes in chlorophyll metabolism, it could know that bract discoloration process accompanied by significant reduction of chlorophyll content and significant increase of flavonoid content. Furthermore, the expression level of chlorophyll biosynthesis key enzyme’s encoding genes, GTS and UROS, were also decreased obviously. As for the chlorophyll degradation key enzyme’s encoding gene, PPH, its expression level increased significantly at the beginning of bracts discoloration, then reduced to close to the lowest level, which in accord with green leaves, after finishing of discoloration. As for the control material, green leaf had the highest chlorophyll content and the lowest flavonoid content. Furthermore, the expression amount of chlorophyll biosynthesis related genes were the highest, while that of degrade related genes was the lowest. This was consistent with colorful plants in chlorophyll and flavonoid pigment change trend. 【Conclusion】 We obtained biosynthesis key enzymes genes, GTS, UROS, and degradation key enzyme gene, PPH, in chlorophyll metabolism pathway from Guzmania. The reason that bracts’ green fade was due to reduction of chlorophyll content, and accompanied by increase of flavonoid content. The reduction of chlorophyll content was due to chlorophyll’s biosynthesis reduced and degradation increased significantly. PPH played a key role in chlorophyll degradation process. The results will provide a basis for researching pigment change of view bract plants.

Key words:  Guzmania Ruiz&Pav, chlorophyll, glutamyl-tRNA synthetase, uroporphyrinogen-III synthase, pheophytin pheophorbide hydrolase/pheophytinase