maintain them in the transgenic plant. Their removal may provide some advantages if the
plant is to be used for another round of transformation because the same selectable marker
gene, if effective, can be used repeatedly. If the safety of the selectable marker to health or
environment is a concern, then it may be useful to have a method to remove it from the plant
before commercialization. Furthermore, it would be essential to remove the selectable
marker gene if it altered plant growth and differentiation. In rare cases, the transformation
frequency may be high enough to recover transgenic plants through screening techniques
Figure 9.11.The green fluorescent protein has been useful for marking whole plants using a
35 S-GFP construct and plant parts such as pollen using a GFP under the control of a pollen-specific
promoter (LAT59) from tomato: (a) 867ms, 200under blue light; (b) 1.7ms, 200under white
light. The arrows in (a) show GFP fluorescence of pollen cells. (Photos courtesy of H. S. Moon
and Neal Stewart.) See color insert.
Figure 9.10.Confocal laser-scanning microscopy of leaf mesophyll cells transiently expressing pep-
tides fused to green fluorescent protein (green image) and yellow fluorescent protein (red image).
Green fluorescent protein is fused to the HDEL tetrapeptide (spGFP-HDEL) to achieve ER retention
and thus reveals the cortical ER network in leaf cells. The proximity of the Golgi to the ER network is
revealed by the yellow fluorescent protein fused to a Golgi glycosylation enzyme (ST-YFP). (Bar¼
10:m.) [Reprinted from Brandizzi et al. (2004), with permission.] See color insert.
234 MARKER GENES AND PROMOTERS