Glutaredoxin Functions in Floral Development

Abstract

Glutaredoxins ({GRXs)} have thus far been associated mainly with redox-regulated processes participating in stress responses. However, {ROXY1}, encoding a {GRX}, has recently been shown to regulate petal primorida initiation and further petal morphogenesis in \emph{Arabidopsis} thaliana. {ROXY1} belongs to a land plant-specific class of {GRXs} that has a {CC-type} active site motif, which deviates from ubiquitously occurring {CPYC} and {CGFS} {GRXs.} Expression studies of yellow fluorescent protein-{ROXY1} fusion genes driven by the cauliflower mosaic virus {35S} promoter reveal a nucleocytoplasmic distribution of {ROXY1.} We demonstrate that nuclear localization of {ROXY1} is indispensable and thus crucial for its activity in flower development. Yeast two-hybrid screens identified {TGA} transcription factors as interacting proteins, which was confirmed by bimolecular fluorescence complementation experiments showing their nuclear interaction in planta. Overlapping expression patterns of {ROXY1} and {TGA} genes during flower development demonstrate that {ROXY1/TGA} protein interactions can occur in vivo and support their biological relevance in petal development. Deletion analysis of {ROXY1} demonstrates the importance of the C terminus for its functionality and for mediating {ROXY1/TGA} protein interactions. Phenotypic analysis of the roxy1-2 pan double mutant and an engineered chimeric repressor mutant from {PERIANTHIA} ({PAN)}, a floral {TGA} gene, supports a dual role of {ROXY1} in petal development. Together, our results show that the {ROXY1} protein functions in the nucleus, likely by modifying {PAN} posttranslationally and thereby regulating its activity in petal primordia initiation. Additionally, {ROXY1} affects later petal morphogenesis, probably by modulating other {TGA} factors that might act redundantly during differentiation of second whorl organs.