PvALF and FUS3 activate expression from the phaseolin promoter by different mechanisms

Abstract

Transcription from the phaseolin (phas) promoter requires two major events: chromatin remodeling, mediated by PvALF, a B3 domain factor, and activation by an ABA-induced signal transduction cascade. Expression from phas is normally seed-specific, but high levels of expression in leaves can be obtained by ectopic expression of PvALF. Here, the system was used to compare the ability of PvALF and Arabidopsis FUS3, another B3 domain transcription factor that lacks the N-terminal activation and B1 domain present in PvALF, to activate phas expression in vegetative tissues. When compared to PvALF-mediated phas activation in the presence of ABA, a delay in phas activation was observed in the presence of both FUS3 and ABA in vegetative tissue. Significant differences in histone modifications at the phas promoter were mediated by FUS3 and PvALF, suggesting that they function through different epigenetic mechanisms. The relationship between PvALF and ABI5, a bZIP transcription factor, in mediating phas expression was also evaluated. Interestingly, over-expression of ABI5 rendered phas expression ABA-independent in the presence of PvALF. Changes in phas activity in different regions within seed embryos were demonstrated using abi5 mutants. Our results show that (1) redundant factors, such as PvALF and FUS3, employ different mechanisms to regulate their common target gene (phas); (2) ABI5, and possibly other redundant bZIP factors, act downstream of ABA in modulating phas expression in the presence of PvALF.

Toward the identification and regulation of the Arabidopsis thaliana ABI3 regulon

“…Therefore, our data do not support the other theoretical possibility that all motif containing promoters are bound by ABI3 and only a fraction becomes selectively activated. If selective promoter binding of ABI3 is a consequence of chromatin remodeling as described for the binding of PsABI3—the Pisum homologue—to the psp54 promoter (95) or if ABI3 binding mediates changes of chromatin structure as described for PvALF—the Phaseolus ABI3 homologue—and stabilizes its own interaction (9,96), is still a matter of debate. …”

Direct targets of the transcription factors ABA-Insensitive(ABI)4 and ABI5 reveal synergistic action by ABI4 and several bZIP ABA response factors

“…Many seed specific genes are repressed during vegetative growth by chromatin remodeling that is dependent on PICKLE (Li et al 2005), BRAHMA (Tang et al 2008), Polycomb group proteins (Makarevich et al 2006), trihelix repressors (Gao et al 2009) and other factors. Previous studies have demonstrated that ectopic expression of B3 domain proteins such as the bean ABI3 homolog (PvALF) and, to a lesser extent, Arabidopsis FUS3 can modify chromatin structure to potentiate expression of seed genes in vegetative tissues upon subsequent induction by ABA (Li et al 1999; Ng and Hall 2008). In addition, ABI3 (or its monocot ortholog VP1) and ABI5 (or its rice homolog TRAB1) display direct and synergistic interactions in two-hybrid analyses in yeast and in transient reporter activation assays in rice protoplasts, consistent with a role for ABI3 in induction as well as potentiation (Finkelstein et al 2005; Gampala et al 2002; Nakamura et al 2001).…”

“…In addition, ABI3 (or its monocot ortholog VP1) and ABI5 (or its rice homolog TRAB1) display direct and synergistic interactions in two-hybrid analyses in yeast and in transient reporter activation assays in rice protoplasts, consistent with a role for ABI3 in induction as well as potentiation (Finkelstein et al 2005; Gampala et al 2002; Nakamura et al 2001). Although ectopic ABI5 expression is not sufficient to activate several seed-specific promoters, partly due to the limited activation potential of ABI5 (Bensmihen et al 2004), co-expression with PvALF renders phaseolin induction ABA-independent (Ng and Hall 2008). Our ectopic ABI5 expression lines lacked overexpressed ABI3 or similar seed transcription factors, and therefore may not have supported the vegetative induction of some genuine ABI5 targets.…”

A novelabi5allele reveals the importance of the conserved Ala in the C3 domain for regulation of downstream genes and salt tolerance during germination inArabidopsis

“…We also speculate that chromatin modification of the Em6 promoter is important for the regulation by ABI5 and ABI3. The seed-specific phaseolin promoter is repressed by histone modification, and PvALF, a Phaseolus vulgaris ABI3 ortholog, is involved in the chromatin remodeling to bring the phaseolin promoter to the potentiated state, which is followed by activation by ABA 37 , 51 , 52 . Since ABI3 and ABI5 interact with each other and the A214G mutation reduced this interaction, ABI5 may also participate in chromatin remodeling with ABI3.…”

“…All abi5 alleles reported to date encode premature proteins terminated in front of the bZIP domain, or are obtained from T-DNA insertion lines—except abi5-3 , which has a small rearrangement adjacent to the 5′ splice site of the final exon 12 , 17 , 36 , 37 . In the present study, we report the first abi5 recessive allele ( abi5-9 ) that encodes a full-length ABI5 protein with one amino acid substitution in the conserved alanine (A214G) of the C3 domain.…”