GRAVITY IS ONE OF THE IMPORTANT MECHANICAL FORCES THAT IS CRITICAL REGULATOR OF PLANT DIRECTIONAL GROWTH PATTERNS THROUGH REPROGRAMMING OF GENE EXPRESSION PATTERNS AND THROUGH DEFINING THE SUBCELLULAR LOCATION OF PROTEINS SUCH AS THE PINFORMED3 AUXIN EFFLUX CARRIER. PLANTS HAVE MULTIPLE SENSORY SYSTEMS THAT RESPOND TO MECHANICAL FORCES INCLUDING GRAVITY TOUCH AND TENSION AT THE CELL TISSUE AND WHOLE-ORGANISM LEVEL. STIMULI INCLUDING GRAVITY TOUCH AND PHYSICAL STRESSES CREATED BY LOCAL CELL EXPANSION AND SUPRACELLULAR PATTERNS OF STRESS CREATED BY CHANGING TISSUE SHAPES IN DEVELOPMENT HAVE SHORT-TERM EFFECTS SUCH AS CREATION OF CELLULAR CALCIUM TRANSIENTS AND TISSUE-WIDE WAVES OVER SECONDS AND MINUTES AND LONG-TERM EFFECTS SUCH AS REORGANIZATION OF THE MICROTUBULE CYTOSKELETON AND ALTERATION OF THE SUBCELLULAR LOCATION OF PROTEINS SUCH AS THE AUXIN EFFLUX CARRIERS THAT OCCUR OVER 2-4 HOURS. THE MOLECULAR COMPONENTS OF GRAVITATIONAL PERCEPTION MECHANISMS AND OF THE SHORT-TERM AND LONG-TERM RESPONSES OF PLANT CELLS AND TISSUES TO MECHANICAL STIMULI OF ALL TYPES ARE ALMOST ENTIRELY UNKNOWN. BOTH ION CHANNELS AND RECEPTOR KINASES HAVE BEEN DEMONSTRATED TO PARTICIPATE IN STIMULUS PERCEPTION OR TRANSDUCTION LEADING TO THE FAST RESPONSES TO PLANT MECHANICAL CHALLENGES. THEY MAY ALSO BE INVOLVED IN REGULATING AUXIN EFFLUX AND THE ORIENTATION AND SEVERING RATE OF THE MICROTUBULE CYTOSKELETON OVER LONGER TIME PERIODS. NASA GENELAB OPENS ACCESS TO RAW DATA DERIVED FROM RESEARCH CONDUCTED ABOARD IN THE INTERNATIONAL SPACE STATION. WE PROPOSE TO UTILIZE THE GENELAB PLANT DATASETS TO SCREEN FOR NOVEL COMPONENTS FUNCTIONING IN PLANT GRAVITY SENSING AND RESPONSE AND IN OTHER RELATED TYPES OF MECHANOPERCEPTION TO CHARACTERIZE THEIR MOLECULAR CELLULAR AND DEVELOPMENTAL FUNCTIONS. OUR PROPOSAL IS BASED ON THE HYPOTHESIS THAT IN SPACE PLANTS MAY REGULATE THEIR OWN GRAVITY SENSORY AND MECHANICAL RESPONSE SYSTEMS AT THE GENE EXPRESSION LEVEL SO AS TO ACCOMMODATE AND HABITUATE TO THE MICROGRAVITY ENVIRONMENT. IN SUPPORT OF THIS HYPOTHESIS OUR PRELIMINARY ANALYSES OF ONE OF THE ARABIDOPSIS DATASETS IN THE GENELAB DATABASE PROVIDE EVIDENCE OF SUBSTANTIAL REGULATORY RESPONSES TO THE SPACE ENVIRONMENT AT THE RNA LEVEL. AMONG OUR PRELIMINARY FINDINGS ARE AN ALTERED EXPRESSION OF MANY ION CHANNEL GENES AND DECREASED EXPRESSION OF CELL WALL-ASSOCIATED GENES. WE WILL FURTHER PROCESS ADDITIONAL RAW DATASETS DERIVED BOTH FROM ARABIDOPSIS AND FERN FROM TWO INDEPENDENT LABORATORIES TO SELECT PUTATIVE TRANSMEMBRANE PROTEINS WITH SIGNIFICANT DIFFERENTIAL EXPRESSION BETWEEN SPACE AND GROUND USING THE AVAILABLE TRANSCRIPTOMIC AND PROTEOMIC DATA. WITH GENE AND PROTEIN LISTS SO DERIVED WE WILL COLLECT NULL MUTANT MATERIALS AVAILABLE AS T-DNA INSERTION LINES FROM PUBLIC COLLECTIONS AND ALSO WILL GENERATE ADDITIONAL KNOCKOUT LINES THROUGH MUTAGENIZING THE TARGET GENES WITH A WELL-TESTED CRISPR/CAS9 SYSTEM NOW IN USE IN OUR LABORATORY. FUNCTIONAL ANALYSIS OF THE MUTANTS WILL BE PERFORMED IN DETAIL USING THE STATE-OF-ART LASER-SCANNING CONFOCAL MICROSCOPY TO ASSESS THE EFFECTS OF THE MUTANTS ON RAPID MECHANICAL RESPONSES SUCH AS CHANGES IN CYTOPLASMIC CALCIUM LEVELS WHICH WILL BE DONE BY INTEGRATING SENSITIVE CALCIUM REPORTERS INTO MUTANT PLANT BACKGROUNDS; AND ON SLOWER CELLULAR RESPONSES SUCH AS PIN1 RELOCALIZATION AND MICROTUBULE CYTOSKELETON REARRANGEMENT AS WELL AS WHOLE PLANT RESPONSES OF ROOT GROWTH AND WAVING AND PHYLLOTACTIC PATTERN ALTERATIONS. THESE STUDIES IF SUCCESSFUL WILL IDENTIFY THE FUNCTIONAL COMPONENTS OF THE GRAVITY AND MECHANICAL RESPONSE PATHWAYS OF PLANTS AND THEREFORE WILL AID IN UNDERSTANDING THE MOLECULAR MECHANISMS AND PROTEIN COMPONENTS OF PLANT GRAVITY AND MECHANICAL STRESS RESPONSE. THIS BROADENED KNOWLEDGE OF PLANT GROWTH MECHANISMS ON EARTH AND IN SPACE WILL BE OF DIRECT BENEFIT TO HUMANS TRAVELING ON EXTENDED SPACE MISSIONS WHERE LONGTERM PLANT GROWTH IN MICROGRAVITY CONDITIONS WILL BE ESSENTIAL.