| Scope and method of study. The objective of this study was to investigate plasmodesmata (PD)-mediated intercellular protein traffic between symplasmically-isolated sieve element (SE)-companion cell (CC) complex and surrounding cells, and between mesophyll (MC) and epidermis (EP) in plants. The fusion protein between Cucumber Mosaic Virus 3a movement protein (3a MP) and green fluorescent protein (GFP) was used as a probe to study protein traffic. The protein was expressed in CC or MC under the control of tissue-specific promoters in transgenic tobacco and Arabidopsis plants. Intercellular protein traffic across specific cellular interfaces and during plant development was analyzed by confocal laser scanning microscopy.;Findings and conclusions. Signal-directed protein traffic between the SE-CC complex and surrounding cells and between MC and EP was discovered. 3a MP:GFP expressed in CC under CC-specific promoters trafficked out the SE-CC complex in all organs at all developmental stages examined in tobacco and Arabidopsis. The movement of 3a MP:GFP was more extensive in tobacco than in Arabidopsis. 3a MP:GFP expressed in MC under an MC-specific promoter trafficked from MC to EP in tobacco source leaves. Our findings suggest that regulated intercellular protein traffic may be one of the mechanisms to establish communication between symplasmic domains, as well as between differentiated tissues. |
