A Pivotal Role of the Basic Leucine Zipper Transcription Factor bZIP53 in the Regulation ofArabidopsisSeed Maturation Gene Expression Based on Heterodimerization and Protein Complex Formation

Abstract

Transcription of Arabidopsis thaliana seed maturation (MAT) genes is controlled by members of several transcription factor families, such as basic leucine zippers (bZIPs), B3s, MYBs, and DOFs. In this work, we identify Arabidopsis bZIP53 as a novel transcriptional regulator of MAT genes. bZIP53 expression in developing seeds precedes and overlaps that of its target genes. Gain-and loss-of-function approaches indicate a correlation between the amount of bZIP53 protein and MAT gene expression. Specific in vivo and in vitro binding of bZIP53 protein to a G-box element in the albumin 2S2 promoter is demonstrated. Importantly, heterodimerization with bZIP10 or bZIP25, previously described bZIP regulators of MAT gene expression, significantly enhances DNA binding activity and produces a synergistic increase in target gene activation. Fulllevel target gene activation is strongly correlated with the ratio of the correspondent bZIP heterodimerization partners. Whereas bZIP53 does not interact with ABI3, a crucial transcriptional regulator in Arabidopsis seeds, ternary complex formation between the bZIP heterodimers and ABI3 increases the expression of MAT genes in planta. We therefore propose that heterodimers containing bZIP53 participate in enhanceosome formation to produce a dramatic increase in MAT gene transcription.

Heterodimers of the Arabidopsis Transcription Factors bZIP1 and bZIP53 Reprogram Amino Acid Metabolism during Low Energy Stress

“…Furthermore, distinct differences in the function of bZIP1 and bZIP53 become obvious when these plants were studied under a normal day/night cycle. As confirmed by immunoblot analysis, high-level expression of bZIP1 did not lead to obvious phenotypic changes, whereas medium-level expression of bZIP53 resulted in significantly reduced plant growth (Alonso et al, 2009). These findings indicate pronounced differences in bZIP1 and bZIP53 function.…”

“…Whereas Pro35S:bZIP1 plants grew normally under standard day-night cycles, Pro35S:bZIP53 plants showed a dwarf growth phenotype that depended on the expression level of the transgene (Alonso et al, 2009). Prolonged cultivation of the bZIP overexpressing lines in the dark resulted in an obvious phenotype ( Figure 1C).…”

The Arabidopsis transcription factor bZIP11 activates auxin-mediated transcription by recruiting the histone acetylation machinery

“…As bZIP11 and -44 showed the strongest activation potential on the GH3.3 promoter in protoplasts, we focused on these TFs applying stably transformed gain-of-function plants. Because constitutive ectopic expression of bZIP11-related bZIPs strongly interferes with plant growth 44,45 , we expressed the bZIPs as HA-tagged versions using a b-estradiol (Est)-inducible expression system (XVE) 46 . Quantitative real-time PCR (qRT-PCR) analysis revealed that GH3.3 induction correlated with an early increase of the bZIP11 regulator, which becomes detectable by immunoblot after 2 h of Est treatment (Fig.…”

“…Hence, these data suggest that bZIPs are not only involved in recruiting the acetylation machinery during auxin-induced transcription. As GREs frequently act as quantitative cis-elements in a wide array of stimulus-induced gene expressions 36,44,54,55 , it is tempting to speculate that GREmediated recruitment of SAGA complexes has a broader impact on gene regulation. Interestingly, the recruitment properties of the bZIPs for specific adapter proteins differ.…”

“…In this respect, the Arabidopsis group C members bZIP10 and -25 also interact with the ADA2b protein, as it has been shown for the closely homologous maize bZIP O2 (refs 29,30). Interestingly, recent publications implicate seedspecific gene regulation with histone acetylation and show that O2 and bZIP10 or bZIP25 (At3g54620) exert related functions in regulation of seed storage protein genes in maize and Arabidopsis 30,44 . Hence, these data suggest that bZIPs are not only involved in recruiting the acetylation machinery during auxin-induced transcription.…”