Exploring broader roles of the plant immune regulator SRFR1 in plant development and defense
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] Tomato plants are attacked by different pathogens, such as the bacterium Pseudomonas syringae pv. tomato that causes tomato speck disease, and herbivores such as Spodoptera exigua caterpillar, which feeds on tomato leaves and fruit, causing tremendous damage. SRFR1 is a nucleocytoplasmic adaptor protein that negatively regulates the plant immune system and has been researched in Arabidopsis plants. Experimental evidence showed that a SRFR1 mutant was able to resist both Pseudomonas syringae pv. tomato strain DC3000 infection and Spodoptera exigua caterpillar herbivory in Arabidopsis plants. The latter occurs because srfr1 can upregulate the JA/ET pathway and suppress the SA pathway during caterpillar feeding, but it is unknown if JA upregulation resulted from chemicals in saliva or caterpillar wounding. In this research, I first measured the morphological differences between the srfr1-1 mutant plant and wild-type RLD to investigate if there are any significant differences between these lines. Results showed that srfr1- 1 leaves are significantly shorter and narrower than those of RLD, but there is no difference between these two lines in petiole length or serration. Also, I mechanically wounded leaves to explore the role of SRFR1 in response to this abiotic stress. The results show that both wild type RLD and srfr1-1 plants respond with similarly decreased growth after manual wounding. This may suggest that JA upregulation in the insect experiments occurred because of the chemical substances in insect saliva or their continuous feeding. In order to extend the Arabidopsis research to Solanum lycopersicum, the main host for Pseudomonas syringae pv. tomato, several steps have been accomplished toward designing an RNAi construct of SRFR1 to generate SRFR1 silenced mutant lines. The full genomic SRFR1 gene was sequenced from the S. lycopersicum cv Rio Grande and its identity to the reference line S. lycopersicum cv Heinz SRFR1 was confirmed. Partial SlSRFR1 cDNAs were cloned into vectors that will be introduced into
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