The Simultaneous Repression of CCR and CAD, TWO Enzymes of the Lignin Essay

The Simultaneous Repression of CCR and CAD, TWO Enzymes of the Lignin Biosynthetic Pathway, Results in Sterility and Dwarfism i - Essay Example Later on, understanding pathways may be used in the laboratory synthesis of these compounds. Moreover, the induction, as well as repression, of their production in plants through anthropogenic intervention to promote optimal plant growth and/or fruit bearing may be conducted. This is important as many secondary metabolites are already used by humans. In the case of lignins, genes CCR and CAD have been identified as the encoders for the last and specific steps for monolignol biosynthesis, the first part of lignin pathway. Because of the complex nature of biochemical production, regulation of a certain pathway may affect other pathways as well. Such effects may be great enough to cause changes in phenotype. In the case of monolignol biosynthesis in tobacco, the silencing of both CCR and CAD genes resulted not only to a reduction of lignin production but to a decrease in plant size as well. The recent study by Thevenin et al. (2011) looked into the effects of silencing monolignol-specif ic CAD and CCR genes in Arabidopsis thaliana. The plant contains two CCR genes, but only one, CCR 1, is specific for lignification. The mutant lines for this gene, irx4, ccr1s and ccr1g, are dwarves, have a reduced amount of lignin (25-35%), and have a modified set of phenolic metabolites. On the other hand, A. thaliana contains nine CAD genes, two of which, CAD C and CAD D, are involved in lignin biosynthesis. CAD C and CAD D double mutants, unlike CCR 1 mutants, has a normal size and 40% amount of lignin. The effects on leaf and flower morphology, lignin structure and content, amount of sugar, and other metabolites were observed. RESULTS Identification and Phenotyping of the ccc Triple Mutant After crossing ccr 1 g mutant with cad c and cad d double mutant, and producing ccc mutant, the absence of CCR 1, CAD C, and CAD D expression in ccc mutants was verified using RT-PCR. 1. Leaf Morphology The growth of wild type, ccc, cad c, cad d, and ccr 1 g from plantlets to senescence were observed at greenhouse conditions. At 30 days, the absence of CCR 1 caused the leaves to change its morphology from rosette to pointed and rolled. The decrease in leaf size was also noted most noticeably among ccc plantlets (5-fold shorter), and less prominently in ccr 1 g (3-fold shorter. On the other hand, the absence of both cad c and cad d expression did not cause any decrease in leaf size. 2. Flower Morphology More changes were observed in the flowers. Similar to leaves, the mature floral stem is smaller in ccc than in ccr 1 g mutants. However, when compared to the wild type, the triple mutant senesced later, despite its first inflorescence being prematurely shriveled. In addition, male flowers are sterile. Despite possessing normal pollens, the anthers were unable to release them. As a result, more than 50% of ccc mutants were not able to undergo seed germination. The ccc triple mutant possesses non-dehiscent anthers Initial flower development and stamen filament elongation we re similar in ccc and wild-type A. thaliana. However, ccc anthers, despite containing pollens whose sizes germinating capability (through Alexander and aniline blue staining) were similar to that of wild-type, did not dehisce as what normally happens. Probably, the absence of lignified secondary thickening observed among ccc plants may have caused the non-dehiscent of anthers. The ccr 1 g plants, on the other hand, have few