A., Walling L. photosynthetic machinery was reduced following the viruliferous whitefly and nonviruliferous whitefly treatments and Oligomycin could possibly be due to reallocation Oligomycin of resources for defense protein synthesis. Signaling-Related Responses Genes encoding two calcium-dependent protein casein kinases and a protein kinase were significantly affected by the wounding treatments. Protein kinases regulated by calcium (Ca 2+ ) play important roles in eukaryotic signal transduction ( Rutschmann et?al. 2002 ). Calcium levels are modulated in response to various signals including light, mechanical manipulation, pathogens, abiotic stress, and hormones ( Sanders et?al. 1999 , Evans et?al. 2001 , Rudd and Franklin-Tong 2001 ), and calcium-dependent protein kinases perform physiological functions in plants from modulating hormone responses, regulating guard cells and stomatal movements, Oligomycin carbon and nitrogen metabolism, mediating abiotic stresses, and pathogen defense (reviewed in Cheng et?al. 2002 ). Influx of calcium ions and the activity of a protein kinase both are required for the JA-pathway induction, systemin-triggered depolarization of the plasma membrane and alkalization of the extracellular space ( Felix and Boller 1995 , Moyen and Johannes 1996 , Moyen et?al. 1998 , Schaller and Oecking 1999 , Schaller and Frasson 2001 ). Schenk et?al. (2000) demonstrated that em A. thaliana /em treated with ethylene upregulated a protein kinase nearly fivefold and expression of casein kinase I in regulation of membrane binding ( Yu and Roth 2002 ). Here, both viruliferous and nonviruliferous whitefly treatments significantly increased signal transduction associated with mediating the host plant response to disease and wounding, suggesting that tomato plants detected the subtle signals from whitefly feeding, and responded to viral pathogen attack. An altered response to gravity (ARG1) protein gene ( Chen et?al. 1998 ) was significantly upregulated in the viruliferous whitefly treatment, compared with the nonviruliferous or the nonwounded treatment. No significant differences were observed between nonviruliferous whitefly feeding and nonwounded plant Oligomycin treatments. AGR1 BCL2L8 encodes a putative transmembrane protein, whose amino acid sequence shares some homology with bacterial transporters ( Chen et?al. 1998 ). The high, increased expression (8.24-fold) of this protein in the virus-infected treatment, although speculative, suggests that this type of transporter may be important in transmembrane interactions with virus particles or viralCprotein complexes that aid in aspects of viral infection and/or spread in the plant. It would be interesting to test for direct interaction between ARG1 and the PepGMV-Di proteins. Cell Wall and Growth-Related Responses In the cell wall and growth-related response category, a putative xyloglucan endotransglycosylase (XET) gene was significantly upregulated in both the whitefly treatments compared with the nonwounded treatment. XETs cleave and link xyloglucan chains resulting in increasing plasticity and elasticity of cell walls for cell growth ( Catal et?al. 2001 , Thompson and Fry 2001 ). They are also induced in response to various developmental and environmental factors such as mechanical stimuli, temperature changes, light, ( Malinowski and Filipecki 2002 ) wounding, and pathogen infection ( Maleck et?al. 2000 , Schenk et?al. 2000 ). Whitefly feeding activity and stylet penetration of the spaces between the cell wall and plasma membrane may be aided by induction of this gene, affecting the plasticity of the cell wall, and allowing for easier penetration of the plant tissue by the insect stylets ( Moran et?al. 2002 ). Hui et?al. (2003) determined that two XET genes were upregulated over twofold and threefold in em N. attenuata /em after em M. sexta /em larvae feeding for 24?h. This suggests that increasing the elasticity of cell walls is not unique to whitefly feeding but rather that it may be a feature associated with insect herbivore feeding in general. Abiotic-Related Responses A gene encoding glucosyltransferase was significantly upregulated in the virus treatment, compared with the nonwounded treatments, and increased expression of glucosyltransferase was observed in the nonviruliferous treatment, compared with the nonwounded plants. Glucosyl-transferases are involved in processes catalyzing transfer of glucose used for synthesis of oligosaccharides, polysaccharides, and other carbohydrates ( Malinowski and Filipecki 2002 ). This suggests that begomovirus infection was associated with the transfer of resources within the plant to aid in the production of compounds responding to begomoviral pathogen infection. A dehydration-induced protein gene was significantly upregulated in the viruliferous whitefly treatment compared with both the nonviruliferous whitefly and nonwounded treatments. These proteins are expressed in response to low temperature stress. In addition, a heat shock protein gene was also significantly expressed in the virus treatment, compared with both the.