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The Involvement of Zinc-Finger Proteins in the Abiotic Stress-Response Network of Arabidopsis thaliana
Biochemistry and Molecular Biology
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Even though plants have many defense and acclimation mechanisms, environmental stresses are still the major cause for crop loss worldwide. All environmental stresses together are estimated to reduce average yields of major crop plants by more than 50% worldwide, whereas yield loss caused by pathogens is estimated at 10-20%. According to USDA, the US loses about $17-19 billion in yield because of environmental stress every year. Increasing abiotic threats such as ozone and drought that accompany global warming force us to understand and manipulate the stress response mechanisms of plants. The regulation of stress responses in plants involves many different factors such as kinases, transcription factors, signaling molecules, and repressors. Recent studies emphasized the importance of repressors in the stress response and defense activation of plants. Some of these repressors are members of the C2H2 zinc finger gene family and contain ERF-associated amphiphilic repression (EAR) domain. Recent studies performed with certain zinc finger family members revealed that some of them are key elements of the stress response pathway of Arabidopsis. In our study, we investigated involvement of three zinc finger proteins in the stress response of Arabidopsis: Zat7, Zat10 and Zat12. Although previous studies have suggested that EAR motif-containing C2H2-type zinc finger proteins are involved in the stress response network of Arabidopsis, it was not clear whether the EAR motif is involved in this function. Our data showes that transgenic plants constitutively expressing Zat7 had enhanced tolerance to salinity. Deletion or mutation of the EAR motif of Zat7 abolished this tolerance. Moreover, a yeast-two hybrid analysis revealed that the EAR motif plays role in protein-protein interaction. Our research with Zat10, another EAR motif-containing C2H2-type zinc finger protein, suggested that Zat10 acts as both a positive and a negative regulator of plant defenses, Recent studies suggested that Zat10 and Zat12 act in a coordinated manner in response to cold stress in Arabidopsis. To analyze the relationship between Zat10 and Zat12 during cold stress, we obtained a Zat10/Zat12 double knockout line. This line showed enhanced sensitivity to cold when compared to wild type, Zat10-knockout or Zat12-knockout plants. Our data suggests that there are at least two different cold stress response pathways in Arabidopsis. One pathway involves Zat10 and the other one involves Zat12. These pathways are linked to each other but act at different time points during the cold stress response. More than 25% of plant genes encode proteins with unknown functions. Although research has suggested that they might play important roles in plants, their function remains unknown. To begin the characterization of these proteins, we choose 41 genes that are up-regulated in response to endogenous oxidative stress. These were stress screened by both over-expressing them in Arabidopsis and in yeast that lacks reactive oxygen species (ROS) scavenging ability. More than 70% of the proteins enhanced the tolerance of transgenic plants to oxidative stress whereas 90% of the proteins did not enhance the tolerance of transgenic plants to other stresses tested. All proteins but one didn't change the response of the yeast to oxidative stress. This study suggested that these proteins are highly specific to plant oxidative stress response pathway. Our study showed that the stress response network of Arabidopsis is highly complex and possibly contains unknown members and pathways that require further investigation. We have also demonstrated that EAR motif containing zinc-finger proteins are key members of stress response network of Arabidopsis and at least some of them act through their EAR motif.