Signal transduction networks are very complex and comprised of many interconnecting pathways. Scaffold proteins in signal integration are emerging as dominant components of signal transduction mechanisms. Several lines of evidence indicate that RACK1 (Receptor for Activated C Kinase) family of protein can play a major role in coordinating different signal transduction pathways by acting as a scaffold protein. Though RACK1s in other organisms have been studied extensively, much less is known about RACKs in plants. The repertoire of RACK1 interacting proteins now includes almost 50 physical interactors and is steadily growing. Although RACK1A from Arabidopsis appears to play a major role in environmental stress response related signal transduction pathways, the molecular mechanisms of RACK1A mediated stress signaling responses are not known. Key preliminary observations indicate that all three family members are capable of interacting with each other and the potential sumoylation site within RACK1 play a major role in the regulation of sub-cellular localization. Promoter::GUS reporter studies reveal that RACK1 genes are ubiquitously expressed and all three genes are expressed in the guard cells, an observation consistent with water-stress resistance phenotype observed in rack1A mutants. In order to better understand RACK1A mediated signal transduction pathways, RACK1 interactors will be identified with a split ubiquitin based cDNA library screen system. Also, the physiological basis of RACK1 dimerization events will be characterized and its sub-cellular localization and tissue specific expression pattern will be determined. As almost identical RACK1 sequences are conserved in wide range of crop plants including rice, tomato, and tobacco; the research will offer an opportunity to enhance agricultural productivity and sustainability by the molecular knowledge gained from this research. Deeper understanding of different stress signal transduction pathways and their interconnectedness will be instrumental in engineering signal transduction mechanisms for crop improvement. Moreover, the research will primarily be undertaken at Howard University, a major university for African-American students. The project is structured to ensure effective participation of minority undergraduate students and introduce them to potential careers in science.
