root uv-b sensitive Mutants Are Suppressed by Specific Mutations in ASPARTATE AMINOTRANSFERASE2 and by Exogenous Vitamin B6

Abstract

Vitamin B6 (vitB6) serves as an essential cofactor for more than 140 enzymes. Pyridoxal 5'-phosphate (PLP), active cofactor form of vitB6, can be photolytically destroyed by trace amounts of ultraviolet-B (UV-B). How sun-exposed organisms cope with PLP photosensitivity and modulate vitB6 homeostasis is currently unknown. We previously reported on two Arabidopsis mutants, rus1 and rus2, that are hypersensitive to trace amounts of UV-B light. We performed mutagenesis screens for second-site suppressors of the rus mutant phenotype and identified mutations in the ASPARTATE AMINOTRANSFERASE2 (ASP2) gene. ASP2 encodes for cytosolic aspartate aminotransferase (AAT), a PLP-dependent enzyme that plays a key role in carbon and nitrogen metabolism. Genetic analyses have shown that specific amino acid substitutions in ASP2 override the phenotypes of rus1 and rus2 single mutants as well as rus1 rus2 double mutant. These substitutions, all shown to reside at specific positions in the PLP-binding pocket, resulted in no PLP binding. Additional asp2 mutants that abolish AAT enzymatic activity, but which alter amino acids outside of the PLP-binding pocket, fail to suppress the rus phenotype. Furthermore, exogenously adding vitB6 in growth media can rescue both rus1 and rus2. Our data suggest that AAT plays a role in vitB6 homeostasis in Arabidopsis.

Consequences of a Deficit in Vitamin B6 Biosynthesis de Novo for Hormone Homeostasis and Root Development in Arabidopsis

“…2002; González et al, 2007), and the short-root phenotype of the rus (for root ultraviolet B-sensitive) mutants (Tong et al, 2008;Leasure et al, 2009) appears to be suppressed by mutations in the PLP-binding site of Asp aminotransferase as well as by pyridoxine supplementation (Leasure et al, 2011). The rus mutants have defects in polar auxin transport (Ge et al, 2010;Yu et al, 2013) and may provide an interesting link to this study.…”

Illumination of Arabidopsis roots induces immediate burst of ROS production

“…15 Besides visible light, roots are very sensitive also to UV-B light with root apex being the most sensitive part of plant roots. [16][17][18][19] Recent study has reported that UVR8 protein is the UV-B receptor both in roots and shoots. 20 In Figure 2, the generation of hydrogen peroxide stained by DAB in the root apex region after 60 min of both white and blue light illumination.…”

The UVR8 UV-B Photoreceptor: Perception, Signaling and Response

“…There are several examples in the literature that tempts one to speculate that plant UV-B signaling may proceed via several routes. These include peak induction of gene expression and production of UV-absorbing pigments in response to distinct wavelengths within the UV-B range and responses that still occur in cop1 and uvr8 seedlings where the UVR8-mediated UV-B signaling pathway is abolished (Ulm et al 2004, Brown and Jenkins 2008, Kalbina et al 2008, Safrany et al 2008, Gardner et al 2009, Shinkle et al 2010, Leasure et al 2011, Lang-Mladek et al 2012. A recent report also indicated that pyrimidine dimers formed under UV-B in DNA may signal to stress-activated MAP kinase signaling (Gonzalez Besteiro and Ulm 2013).…”