PCR (polymerase chain reaction) is a widely used method for amplifying DNA sequences. PCR can be used to amplify DNA from a variety of sources, including genomic DNA, cDNA, and synthetic DNA. However, PCR can be time-consuming and expensive, and it can be difficult to obtain high yields of the amplified DNA.

Cell-free protein expression is a method of producing proteins from genes in a cell-free system. This method does not require the use of living cells, making it a good option for genes that are difficult to express in cells or for genes that produce toxic proteins.

Cell-free protein expression is a relatively new method that is becoming increasingly popular. Ultimately, the best way to amplify the coding sequence of a gene of interest for expression purposes will depend on the specific gene and the desired application.

Good plasmids are the pBin19 vector, a broad-host-range plasmid that can be used in a variety of plant species. The pCAMBIA1301 vector is a binary vector that is specifically designed for plant transformation. The pGreenII vector is a plant-specific vector that can be used to express genes in a variety of plant tissues.

Agrobacterium tumefaciens, Arabidopsis thaliana, Nicotiana tabacum (tobacco)are all good hosts for the plants.

You can run your partial protein sequence in a Blast search to see whether other plants (many of which are of course fully sequenced) have the same gene. By analyzing the relatedness of those genes you can use the sequence from close relative species for your PCR or you can design redundant primers that would amplify the gene from a broad range of plants and see if that works.

Alternately you can design primers from the protein sequence you have and try to do inverse PCR to get adjacent DNA and sequence that so you have actual DNA sequence of your gene of interest.