The regulation of Hsp33's chaperone function is highly sophisticated. On a transcriptional level, Hsp33 is under heat shock control. This increases the concentration of Hsp33 under heat and oxidative stress, a process that favors dimerization, a critical step in Hsp33's activation reaction. On a posttranslational level, Hsp33 is redox regulated. Dimerization of disulfide-bonded Hsp33 monomers leads to the formation of two extended, putative substrate binding sites. These sites might explain Hsp33's high and promiscuous affinity for unstructured protein folding intermediates.

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The two homologous genes, NIA1 and NIA2, encode nitrate reductases in Arabidopsis, which govern the reduction of nitrate to nitrite. This step is the rate-limiting step of the nitrate assimilation and utilization. Therefore, the regulation of NIA1 and NIA2 is important for plant development and growth. Although they are similar in sequence and structure, their regulations are different. Genetic analysis uncovers that NIA1, rather than NIA2, plays a predominant role in adopting to ABA stress. Although both long-term stress conditions can cause an improvement in NIA1 levels, a decrease in NIA1 levels under short-term treatments seems to be necessary for plants to switch from the growth status into the adopting status. Interestingly, the downregulation of the NR is distinct under different stress conditions. Under ABA treatment, the NR proteins are degraded via a 26S-proteasome dependent manner, while the transcriptional regulation is the main manner to rapidly reduce the NIA1 levels under nitrogen deficiency and NaCl stress conditions. These results indicate that under stress conditions, the regulation of NIA1 is complex, and it plays a key role in regulating the balance between growth and adaptation.

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