Ha-Young Jang

The Camelina aquaporin CsPIP2;1 is regulated by phosphorylation at Ser273, but not at Ser277, of the C-terminus and is involved in salt- and drought-stress responses

Aquaporin (AQP) proteins are involved in water homeostasis in cells at all taxonomic levels of life. Phosphorylation of some AQPs has been proposed to regulate water permeability via gating of the channel itself. We analyzed plasma membrane intrinsic proteins (PIP) from Camelina and characterized their biological functions under both stressful and favorable conditions. A three-dimensional theoretical model of the Camelina AQP proteins was built by homology modeling which could prove useful in further functional characterization of AQPs. CsPIP2;1 was strongly and constitutively expressed in roots and leaves of Camelina, suggesting that this gene is related to maintenance of homeostasis during salt and drought stresses. CsPIP2s exhibited water channel activity in Xenopus oocytes. We then examined the roles of CsPIP2;1 phosphorylation at Ser273 and Ser277 in the regulation of water permeability using phosphorylation mutants. A single deletion strain of CsPIP2;1 was generated to serve as the primary host for testing AQP expression constructs. A Ser277 to alanine mutation (to prevent phosphorylation) did not change CsPIP2;1 water permeability while a Ser273 mutation to alanine did affect water permeability. Furthermore, a CsPIP2;1 point mutation when ectopically expressed in yeast resulted in lower growth in salt and drought conditions compared with controls, and confirmation of Ser273 as the phosphorylation site. Our results support the idea that post-translational modifications in the Ser273 regulatory domains of the C-terminus fine tune water flux through CsPIP2;1.

Overexpression of Jatropha aquaporin genes, JcPIP1 and JcPIP2, does not alter response to salt and drought stresses in transgenic arabidopsis

The heterologous expression of PIP1 and PIP2 in plants is a useful strategy for engineering plants, altered to enhance salt and drought tolerance. In order to further understand the functions of JcPIP1 and JcPIP2 under salt and drought stresses, we generated transgenic Arabidopsis plants overexpressing JcPIP1 or JcPIP2. Transgenic plants did not exhibit improved tolerance against salt and drought stresses compared to WT (Col-0) in seed germination and root elongation. However, results have shown that the total plant growth exhibited improved total plant and rosette leaf growth. The relative water contents (RWC) results showed that, overall, lines have a higher RWC under salt stress than drought stress. However, the transcript levels of several salt stress-responsive genes led us to propose that the unchanged growth of transgenic Arabidopsis plants under salt and drought stresses is due, at least in part, to modulation of the expression of the salt stress-responsive genes by JcPIP1 or JcPIP2. Taken together, these results suggest that overexpression of JcPIP1 and JcPIP2 in Arabidopsis was not altered response to salt and drought stresses.