Plant Biology- Please also explain why! 1. You make a transgenic plant containin
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Question
Plant Biology- Please also explain why!
1. You make a transgenic plant containing a chimeric gene consisting of the 35S promoter fused with the gene encoding expansin (35S:EXP). The 35S promoter is active at a high level in most cells of the plant. Therefore, the plant will overproduce expansin throughout the plant, including the stem. You use stem segments that were frozen and thawed from non-transgenic and transgenic 35S:EXP plants in experiments to measure stem segment extension. Which stem segment would exhibit more cell wall extension in pH 7.0 buffer? Which stem segment would exhibit more cell wall extension in pH 4.5 buffer? Explain your answer.
2. You identify a protein designated X that you believe colocalizes with both CesA and microtubules. Protein X is not required for CesA catalytic activity, and it is able to bind microtubules. Design an experiment to determine if protein X colocalizes with both CesA and microtubules. Suggest a role for protein X in cell wall biosynthesis if it colocalizes with CesA and microtubules.
Explanation / Answer
1. Genetic transformation aims to introduce gene with desirable trait into plant for a particular purpose and geographical location(s). According to need, the gene is transferred with specific promoter to obligate its expression either all the time or at particular time and tissue. A variety of diverse promoters are convenient that regulate the degree of expression of a transgene, obtained from various sources. The specificity of a promoter is crucial in controlling expression of transgene in target tissue or in whole plant. Among the different plant promoters, the constitutive promoter, like CaMV 35S is most commonly used in plant genetic transformation particularly in dicots. However, the risk involved in the use of constitutive promoter is its release into the environment through horizontal gene transfer causing adverse effects on non-target organisms and eco-system. Therefore, the importance of inducible promoter is to increase the expression of genes in a particular tissue or at specific developmental stage(s). Genetic engineered crops sometimes raise problem to biosafety concern when selectable marker gene is used that causes adverse effects on organisms. So, it is the responsibility of researchers to develop a baseline for the acceptance of risk free transgenic crop to the consumers.
2. Cellulose synthesis in the developing xylem vessels of Arabidopsis requires three members of the cellulose synthase (CesA) gene family. In young vessels, these three proteins localize within the cell, whereas in older vessels, all three CesA proteins colocalize with bands of cortical microtubules that mark the sites of secondary cell wall deposition. In the absence of one subunit, however, the remaining two subunits are retained in the cell, demonstrating that all three CesA proteins are required to assemble a functional complex. CesA proteins with altered catalytic activity localize normally, suggesting that cellulose synthase activity is not required for this localization. Cortical microtubule arrays are required continually to maintain normal CesA protein localization. By contrast, actin microfilaments do not colocalize with the CesA proteins and are unlikely to play a direct role in their localization. Green fluorescent protein-tagged CesA reveals a novel process in which the structure and/or local environment of the cellulose synthase complex is altered rapidly.
Phylogenetic analyses of cellulose synthase (CesA) and cellulose synthase-like (Csl) families from the cellulose synthase gene superfamily were used to reconstruct their evolutionary origins and selection histories. Counterintuitively, genes encoding primary cell wall CesAs have undergone extensive expansion and diversification following an ancestral duplication from a secondary cell wall-associated CesA. Selection pressure across entire CesA and Csl clades appears to be low, but this conceals considerable variation within individual clades. Genes in the CslF clade are of particular interest because some mediate the synthesis of (1,3;1,4)-?-glucan, a polysaccharide characteristic of the evolutionarily successful grasses that is not widely distributed elsewhere in the plant kingdom. The phylogeny suggests that duplication of either CslF6 and/or CslF7 produced the ancestor of a highly conserved cluster of CslF genes that remain located in syntenic regions of all the grass genomes examined. A CslF6-specific insert encoding approximately 55 amino acid residues has subsequently been incorporated into the gene, or possibly lost from other CslFs, and the CslF7 clade has undergone a significant long-term shift in selection pressure. Homology modeling and molecular dynamics of the CslF6 protein were used to define the three-dimensional dispositions of individual amino acids that are subject to strong ongoing selection, together with the position of the conserved 55-amino acid insert that is known to influence the amounts and fine structures of (1,3;1,4)-?-glucans synthesized. These wall polysaccharides are attracting renewed interest because of their central roles as sources of dietary fiber in human health and for the generation of renewable liquid biofuels.