1. The most easy way is to send to a company to do that for you. They will check rice codon usage, and replace rare codons in Candida tropicalis with rice codons. We used GenScript for our codon optimization [ http://www.genscript.com/codon-opt.html?src=google&gclid=CjwKEAjwsMu5BRD7t57R1P2HwBgSJABrtj-RCqlgV-8M_SHuNDflp74rPjGgZ4tYT33uHbzx3j5QoxoCzCzw_wcB ]
2. Do you know whether this yeast gene (in native form) express well in rice?
Some native bacterial genes express as well as its optimized version in plants. No need for optimization.