Assistant Professor Tuskegee University Tuskegee, Alabama
Body of Abstract: The SCR, a transcription factor, plays a vital role in numerous developmental phenomena in Arabidopsis thaliana. The confirmed functions of SCR include the radial patterning of axial organs, the development of endodermis and normal shoot gravitropism. The SCR gene is expressed in endodermis of shoots, as well as endodermis and quiescent center of roots, and the bundle sheath of leaves. Notably, scr mutant plants exhibit shoot agravitropism, abnormal radial pattern in both shoots and roots and short root phenotype. To expand our knowledge about SCR gene function, to identify the location of SCR expression pattern/level driven by 35S promoter in Arabidopsis thaliana and to examine the broader effects of SCR gene missexpression in scr mutant and WS plants transgenic lines with different domains of SCR expression were generated. Hypocotyls of two lines 35S::GFP::SCR/scr1(st1) and 35S::SCR/scr1(D7) showed gravitropic response similar to WS plants while one 35S::SCR/WS (35S) line plant hypocotyls showed complete agravitropism. The cross-section analysis revealed that st1 and D7 have not rescued their normal radial pattern. Both contain only two ground tissue layers. However, the 35S continue to have normal radial pattern with three ground tissue layers. The analysis of amyloplast sedimentation in 35S, st1 and D7 demonstrated that presence and location of amyloplast in 35S are comparable to those in WS, whereas st1 and D7 exhibit similarities to scr1. These findings provide evidence supporting our hypothesis that normal radial pattern is not essential for normal gravitropic responses. Furthermore, they suggest the presence of at least one amyloplast- independent pathway for gravity sensing in the hypocotyl.