DISSECTION OF MOLECULAR MECHANISMS OF ABIOTIC STRESS TOLERANCE IN ARABIDOPSIS THALIANA
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Plants, due to their sessility nature, must cope with different environmental stresses during their lifetime. Elucidation of the molecular mechanisms of abiotic stress responses in plants is important for agricultural production, food security, and global sustainability. For my dissertation research, we employed forward genetic analysis to study genes essential for different abiotic stresses in Arabidopsis thaliana. Here we report the identification and characterization of two genes ROA1 (REGULATOR OF ABA RESPONSE 1) and RSA4 (SHORT ROOT IN SALT MEDIUM 4), that are critical for cold stress and salt stress responses, respectively. ROA1 is a splicing factor, belonging to U1 snRNPs (small nuclear ribonucleoproteins). A previous study in our laboratory revealed its regulatory roles in ABA responses. Here, we characterized its role in plant cold stress responses, especially its role in chilling stress tolerance. The roa1 mutants are hypersensitive to chilling stress and moderate sensitive to freezing stress. Overexpressing ROA1 led to improved chilling tolerance. These results suggest that ROA1 positively regulates plant cold tolerance. RNA sequencing data revealed that ROA1 controls the proper splicing of many genes with diverse functions. IP-Mass analysis together with BiFC analysis showed that ROA1 interacts with other U1 snRNPs such as U1-70K and PRP40A. Loss-of-function of one of the ROA1 splicing targets, AtDi19-4 (Drought-responsive family protein 19-4), is hypersensitive to chilling stress. Ectopic expression of AtDi19-4 can partially restore the roa1 mutant phenotype, suggesting it is critical for ROA1 function under cold stress. Together these results indicate that ROA1 is critical for alternative splicing of genes under cold and cold stress tolerance in plants.We identified the rsa4 mutant in a forward genetic screening. RSA4 encodes a cellulose synthase for primary cell wall synthesis. rsa4 mutants are sensitive to salt stress and drought stress. The rsa4 mutants over accumulate reactive oxygen species (ROS). We also observed that the integrity of the cuticle in the rsa4 mutant plants is compromised. These results can at least partially explain why mutations in RSA4 result in increased sensitivity to salt and drought stress conditions.