M. Bellucci et al., Accumulation of maize gamma-zein and gamma-zein: KDEL to high levels in tobacco leaves and differential increase of BiP synthesis in transformants, THEOR A GEN, 101(5-6), 2000, pp. 796-804
gene constructs (pROK.TG1L and pROK.TG1LK) were utilized to achieve accumul
ation of maize gamma -zein to high levels in tobacco (Nicotiana tabacum L.)
leaves. Both the chimaeric genes contained the gamma -zein-coding region p
receded by the 5'untranslated leader from the coat protein mRNA of TMV, but
one of them (pROK.TG1LK) was modified in its protein-coding region by the
addition of the ER retention signal KDEL. The accumulation of gamma -zein a
nd gamma -zein:KDEL in leaves was compared with heterologous protein accumu
lation in tobacco plants previously transformed with a gamma -zein cDNA har
bouring a native 5'UTR. Replacement of gamma -zein 5'UTR with the TMV leade
r dramatically increased gamma -zein production. Furthermore, gamma -zein:
KDEL-expressing plants, on average, accumulated twice as much foreign prote
in in their leaves as pROK.TG1L plants. The twofold increase in the level o
f gamma -zein:KDEL can probably be attributed to an improvement in the mech
anism for ER retention of zeins in the transgenic cells. Transformants also
showed increased production of BiP, though to a lesser extent in gamma -ze
in:KDEL-expressing plants compared with pROK.TG1L plants. it is therefore l
ikely that gamma -zein:KDEL retention is made less dependent on the chapero
ne assistance of BiP by the presence of the KDEL signal on the gamma -zein
mutant.