KEY MESSAGE : bZIP TF network in pollen. Transcriptional control of gene expression represents an important mechanism guiding organisms through developmental processes and providing plasticity towards environmental stimuli. Because of their sessile nature, plants require effective gene regulation for rapid response to variation in environmental and developmental conditions. Transcription factors (TFs) provide such control ensuring correct gene expression in spatial and temporal manner. Our work reports the interaction network of six bZIP TFs expressed in Arabidopsis thaliana pollen and highlights the potential functional role for AtbZIP18 in pollen. AtbZIP18 was shown to interact with three other pollen-expressed bZIP TFs-AtbZIP34, AtbZIP52, and AtbZIP61 in yeast two-hybrid assays. AtbZIP18 transcripts are highly expressed in pollen, and at the subcellular level, an AtbZIP18-GFP fusion protein was located in the nucleus and cytoplasm/ER. To address the role of AtbZIP18 in the male gametophyte, we performed phenotypic analysis of a T-DNA knockout allele, which showed slightly reduced transmission through the male gametophyte. Some of the phenotype defects in atbzip18 pollen, although observed at low penetrance, were similar to those seen at higher frequency in the T-DNA knockout of the interacting partner, AtbZIP34. To gain deeper insight into the regulatory role of AtbZIP18, we analysed atbzip18/- pollen microarray data. Our results point towards a potential repressive role for AtbZIP18 and its functional redundancy with AtbZIP34 in pollen.

Laboratory of Cell Biology Institute of Experimental Botany AS CR v v i Rozvojová 263 165 02 Prague 6 Czech Republic Laboratory of Pavel Jungwirth Institute of Organic Chemistry and Biochemistry AS CR v v i Flemingovo nám 2 166 10 Prague 6 Czech Republic

Laboratory of Hormonal Regulations in Plants Institute of Experimental Botany AS CR v v i Rozvojová 263 165 02 Prague 6 Czech Republic

Laboratory of Pollen Biology Institute of Experimental Botany AS CR v v i Rozvojová 263 165 02 Prague 6 Czech Republic

Laboratory of Pollen Biology Institute of Experimental Botany AS CR v v i Rozvojová 263 165 02 Prague 6 Czech Republic Department of Physiology Faculty of Science Charles University Prague Viničná 7 128 44 Prague 2 Czech Republic Institute of Physiology AS CR v v i Vídeňská 1083 142 20 Prague 4 Czech Republic National Institute of Mental Health Topolová 748 250 67 Klecany Czech Republic

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