Influence of the tobacco mosaic virus 30-kDa movement protein on carbon metabolism and photosynthate partitioning in transgenic tobacco plants

Abstract

Abstract. Transgenic tobacco (Nicotiana tabacum L.)plants expressing the 30-kDa movement protein of tobacco mosaic virus (TMV-MP) were employed to investigate the influence of a localized change in mesophyllbundle sheath plasmodesmal size exclusion limit on photosynthetic performance and on carbon metabolism and allocation. Under conditions of saturating irradiance, tobacco plants expressing the TMV-MP were found to have higher photosynthetic CO2-response curves compared with vector control plants. However, this difference was significant only in the presence of elevated CO2 levels. Photosynthetic measurements made in the greenhouse, under endogenous growth conditions, revealed that there was little difference between TMV-MP-expressing and control tobacco plants. However, analysis of carbon metabolites within source leaves where a TMV-MP-induced increase in plasmodesmal size exclusion limit had recently taken place established that the levels of sucrose, glucose, fructose and starch were considerably elevated above those present in equivalent control leaves. Although expression of the TMV-MP did not alter total plant biomass, it reduced carbon allocation to the lower region of the stem and roots. This difference in biomass distribution was clearly evident in the lower root-to-shoot ratios for the TMV-MP transgenic plants. Microinjection (dye-coupling) studies established that the TMV-MP-associated reduction in photosynthate delivery (allocation) to the roots was not due to a direct effect on root cortical plasmodesmata. Rather, this change appeared to result from an alteration in phloem transport from young source leaves in which the TMV-MP had yet to exert its influence over plasmodesmal size exclusion limits. These results are discussed in terms of the rate-limiting steps involved in sucrose movement into the phloem.

Comparative studies of compatible and incompatible pepper-Tobamovirus interactions and the evaluation of effects of 24-epibrassinolide

“…Altered carbohydrate metabolism and partitioning was observed also in transgenic tobacco plants overexpressing the movement protein coding gene of Tobacco mosaic virus. Contents of sucrose, glucose, fructose, and starch were elevated in source leaves of transgenic tobacco plants (Lucas et al 1993). The accumulated monosaccharides may be necessary as a source of carbon and energy for defense responses.…”

Influence of Environmental Stress on Biomass Partitioning in Transgenic Tobacco Plants Expressing the Movement Protein of Tobacco Mosaic Virus

“…We chose one line of transgenic tobacco plant for the present experiments, since previous studies with a number of independent transformed lines clearly established that expression of the TMV-MP reduces biomass partitioning to roots and alters carbon allocation in a11 of these transgenic plants (Lucas et al, 1993;Balachandran et al, 1995;Olesinski et al, 1995). Seeds were germinated on a soil mixture and 4-week-old seedlings were transplanted into plastic pots containing sand.…”

“…Although the root-to-shoot ratio was increased by N or P deficiencies, the TMV-MP-induced alteration in biomass partitioning was not overcome. Transgenic tobacco (Nicotiana tabacum) plants expressing the MP of TMV exhibit an increase in sugar and starch levels within mature leaves, as well as a reduction in partitioning of biomass to roots, when compared with vector control plants (Lucas et al, 1993; Balachandran et al, 1995; Olesinski et al, 1995). The mechanism(s) through which the TMV-MP affects carbon allocation and biomass partitioning in transgenic tobacco plants has yet to be elucidated.…”

The Rubisco Small Subunit Is Involved in Tobamovirus Movement and Tm-22-Mediated Extreme Resistance

“…Consistent with this hypothesis, TMV MP does affect carbohydrate metabolism and photoassimilate translocation during TMV infection. Transgenic overexpression of TMV MP resulted in palegreen leaves, elevated carbohydrate accumulation, and reduced rates of photoassimilate export in source leaves (Lucas et al, 1993;Olesinski et al, 1995Olesinski et al, , 1996Almon et al, 1997). Furthermore, TMV MP induced alterations in carbon partitioning in the mesophyll and is involved in regulating photosynthesis.…”