The transcript elongation factor FACT affects Arabidopsis vegetative and reproductive development and genetically interacts with HUB1/2

Abstract

SUMMARYThe facilitates chromatin transcription (FACT) complex, consisting of the SSRP1 and SPT16 proteins, is a histone chaperone that assists the progression of transcribing RNA polymerase on chromatin templates by destabilizing nucleosomes. Here, we examined plants that harbour mutations in the genes encoding the subunits of Arabidopsis FACT. These experiments revealed that (i) SSRP1 is critical for plant viability, and (ii) plants with reduced amounts of SSRP1 and SPT16 display various defects in vegetative and reproductive development. Thus, mutant plants display an increased number of leaves and inflorescences, show early bolting, have abnormal flower and leaf architecture, and their seed production is severely affected. The early flowering of the mutant plants is associated with reduced expression of the floral repressor FLC in ssrp1 and spt16 plants. Compared to control plants, reduced amounts of FACT in mutant plants are detected at the FLC locus as well as at the locations of housekeeping genes (whose expression is not affected in the mutants), suggesting that expression of FLC is particularly sensitive to reduced FACT activity. Analysis of double mutants that are affected in the expression of both FACT subunits and factors catalysing the mono-ubiquitination of histone H2B (HUB1/2) demonstrates that they genetically interact to regulate various developmental processes (i.e. branching, leaf venation pattern, silique development) but independently regulate the growth of leaves and the induction of flowering.

Comparison of the genetic determinism of two key phenological traits, flowering and maturity dates, in three Prunus species: peach, apricot and sweet cherry

“…Accumulation of PIF3 in the nucleus in dark requires COP1, and red and far-red light induce rapid degradation of the PIF3 protein (Bauer et al, 2004). Mutant plants, with reduced amounts of FACT subunit SPT16, have a reduced expression of the floral repressor FLC and bloom early (Lolas et al, 2010).…”

Flickin’ the ubiquitin switch

“…51 Unexpectedly, the results of double mutant analysis suggest that HUB1 and SSRP1/ SPT16 have independent effects on flowering, despite both regulating levels of the FLC gene, which encodes a MADS-box repressor. 46 FACT and H2B ubiquitylation do, however, appear to affect certain phenotypes (leaf shape and venation, silque size) through the same pathway (Fig. 4).…”

“…Ubiquitylation and deubiquitylation of H2B are important at multiple stages of development in Arabidopsis. 16,[41][42][43][44][45][46][47] Mutations in the plant orthologues of dBre1, HUB1 and HUB2, cause a reduction in seed dormancy and plant size, as well as other pleiotropic phenotypes. 16,42 Four independent studies later found that mutant alleles of hub1 and hub2 give rise to an early-flowering phenotype.…”

“…16,[42][43][44][45][46] The FACT (FAcilitates Chromatin Transcription) complex is a transcription elongation factor that also interacts synergistically with H2Bub1 in yeast and humans. 51 Unexpectedly, the results of double mutant analysis suggest that HUB1 and SSRP1/ SPT16 have independent effects on flowering, despite both regulating levels of the FLC gene, which encodes a MADS-box repressor.…”

“…4). 46 Requirement for deubiquitylation. Consistent with a reported role for both H2B ubiquitylation and deubiquitylation in transcriptional elongation, a recent study has demonstrated a requirement for the Arabidopsis H2B ubiquitin protease UBP26 (homologous to human USP31; Table 1) in driving expression of FLC.…”