Molecular Adaptation of Plants to the Environment: Changes in Root Architecture and In

Molecular adaptation of plants to the environment: changes in root architecture and in ion and protein homeostasis

Dudy Bar-Zvi, Doron Shkolnik-Inbar, Guy Adler and Petra Peharec-Stefanic– Ben Gurion University of the Negev, Israel

Plants respond to changes in the environment by physiological, biochemical, molecular and developmental changes leading to adaptation to the altered conditions. This reponse includes global changes in the profile of expressed genes and proteins.

Mutants of the ABSCISIC ACID INENSITIVE (ABI) 4 gene,encoding an AP2-domain transcription factor, were isolated by screening of Arabidopsis seedlings germinating in the presence inhibitory chemicals such as ABA, sucrose or NaCl. ABI4, was assumed to play role mainly in seed maturation and germination. We show that ABI4 is also expressed in roots of mature plants. We have recently shown that ABI4 modulate the ABA and cytokinin inhibition of lateral root formation by inhibiting the polar transport of auxin (Shkolnik-Inbar and Bar-Zvi (2010) Plant Cell 22, 3560–3573). We have also further studied the effects of ABI4 on plant performance under salinity. abi4 mutants display increased salt tolerance also at mature stages. Overexpressing ABI4 resulted in enhanced sensitivity to NaCl. Upon exposure to salt, the abi4 mutants accumulated reduced levels of sodium, compared with WT plants. The ABI4-target gene whose change in expression results in enhancing salt-tolerance of the abi4 mutants was identified. We have shown by chromatin immunoprecipitation (ChIP) that ABI4 binds in planta the promoter of this gene. The ABI4 DNA-binding sites on the promoter were characterized using electrophoretic mobility shift assay (EMSA) of WT and mutated sequences. This study demonstrates that ABI4 has a central role in the modulation of root development and root activities in response to abiotic stresses.

Abiotic stressesalso lead to changes in the protein profiles within plant cells. This includes hundreds of proteins that are either increased or decreased. Controlled protein degradation is thus required to eliminate proteins whose levels should be reduced under stress conditions, and to remove proteins that are irreversibly damaged due to the stress conditions. The Ubiquitin-Proteasome System (UPS) is the central mechanism for controlled protein degradation in the cytosol and nucleus. In this pathway, proteins that are designated for degradation are first tagged with short oligomer of ubiquitin. The resulting ubiquitinated proteins are than being degraded by the proteasome. We have identified a number of mutants in genes encoding ubiquitin-ligases that display increased drought sensitivity. These mutants as well as plants overexpressing these genes were studied. We have used yeast-2-hybrid screening to identify potential targets of these enzymes.