Characterization of transgenic tobacco plants carrying small subunit ADPglucose pyrophosphorylase cDNAs from sweet potato

In order to test a possibility of forming an active ADPglucose pyrophosphor ylase (AGPase) by homotetrameric composition of single subunit in plant, tr ansgenic tobacco plants were generated with two previously isolated cDNAs ( sTL1 and sTL2) encoding the small subunit of sweet potato AGPase. Transform ation was carried out with a mixture of the binary vectors, pMBP1-sTL1 and -sTL2, under the control of CaMV 35S promoter. The PCR analysis of the rand omly selected fifteen transgenic plants showed that ten transgenic lines we re transformed by sTL1 and seven lines by sTL2. Only two transgenic lines w ere transformed with sTL1 and sTL2. The integrated sTL1 and/or sTL2 were ac tively transcribed. The steady-state transcript levels of the transgenic pl ants were higher than those of nontransgenic plants. The sTL1-transformed l ines showed higher transcript levels than sTL2-transformed lines did althou gh the transcript levels were variable among transgenic lines. Despite the differential expression of AGPase mRNA between nontransgenic and transgenic plants, there was no significant difference in the activities of AGPase, i ndicating no sweet potato AGPase activity in transgenic tobacco plants. The immunoblot analysis of the small subunit polypeptide showed that the prote in levels remained unchanged in transgenic plants. The overexpressed transc ripts of sweet potato AGPase small subunit in tobacco plants do not seem to produce an active form of AGPase.