The document discusses using phosphomannose isomerase (PMI) as a selectable marker gene for plant transformation. PMI allows the use of mannose as a carbon source, conferring an advantage for transformed cells. Commonly used antibiotic resistance markers are undesirable for commercial crops. PMI shows potential as an alternative selectable marker since it occurs naturally in some plants and mannose is non-toxic. Further research is needed to optimize PMI expression for reliable selection in more plant species.