Rice tillering is a multigenic trait that influences grain yield, but its regulation molecular module is poorly understood. Here we report that OsMADS57 interacts with OsTB1 (TEOSINTE BRANCHED1) and targets D14 (Dwarf14) to control the outgrowth of axillary buds in rice. An activation-tagged mutant osmads57-1 and OsMADS57-overexpression lines showed increased tillers, whereas OsMADS57 antisense lines had fewer tillers. OsMIR444a-overexpressing lines exhibited suppressed OsMADS57 expression and tillering. Furthermore, osmads57-1 was insensitive to strigolactone treatment to inhibit axillary bud outgrowth, and OsMADS57’s function in tillering was dependent on D14. D14 expression was downregulated in osmads57-1, but upregulated in antisense and OsMIR444a-overexpressing lines. OsMADS57 bound to the CArG motif [C(A/T)TTAAAAAG] in the promoter and directly suppressed D14 expression. Interaction of OsMADS57 with OsTB1 reduced OsMADS57 inhibition of D14 transcription. Therefore, OsMIR444a-regulated OsMADS57, together with OsTB1, target D14 to control tillering. This regulation mechanism could have important application in rice molecular breeding programs focused on high grain yield.

ORCID ID: 0000-0003-4364-778x (K.C.).Brassinosteroids (BRs) regulate many physiological processes during plant development, including flowering. However, little is known about the components of BR signaling that mediate flowering. Here, we report that BRASSINAZOLE-RESISTANT1 (BZR1), the conformation of which is altered by a cyclophilin (CYP20-2), binds cis-elements in the FLOWERING LOCUS D (FLD) promoter to regulate flowering. Both bzr1-1D and fld-4 showed delayed flowering. Electrophoretic mobility shift assay and chromatin immunoprecipitation revealed that BZR1 bound to a putative BR response cis-element and suppressed the expression of FLD. Overexpression of FLD partially rescued the late flowering of pBZR1:mBZR1 Pro234-Leu -CFP (mx3). Yeast two-hybrid and pull-down assays demonstrated that BZR1 interacts with CYP20-2. Arabidopsis thaliana CYP20-2 had greater peptidyl-prolyl cis-trans isomerase activity than did wheat (Triticum aestivum) CYP20-2. Fourier transform infrared spectroscopy revealed conformation changes in BZR1, dependent on interaction with CYP20-2. Due to differences in activity and substrate preference between CYP20-2 proteins from wheat and Arabidopsis, At-CYP20-2-overexpressing lines showed earlier flowering, whereas Ta CYP20-2 lines flowered later. Immunoblot and chromatin immunoprecipitation assays showed that histone H3 trimethyl Lys4 and H3 acetylation levels were negatively correlated with the transcription of FLD (a putative histone demethylase) in various lines. Therefore, a conformational change of BZR1 mediated by CYP20-2 causes altered flowering through modulation of FLD expression.

Vernalization, the requirement of plants for long-term exposure to low environmental temperature for flowering, is an epigenetic phenomenon. Histone modification regulation has been revealed in vernalization, but is limited to key genes. Now, we know that VRN1 is epigenetically critical for monocots. Genome-wide analysis is still unavailable, however. We performed chromatin immunoprecipitation-sequencing for H3K4me3/H3K27me3 in Brachypodium distachyon to obtain a global view of histone modifications in vernalization on a genome-wide scale and for different pathways/genes. Our data showed that H3K4me3 and H3K27me3 play distinct roles in vernalization. Unlike H3K4me3, H3K27me3 exhibited regional regulation, showed main regulation targets in vernalization and contributed to epigenetic memory. For genes in four flowering regulation pathways, only FT2 (functional ortholog of VRN3 in B. distachyon) and VRN1 showed coordinated changes in H3K4me3/H3K27me3. The epigenetic response at VRN3 was weaker under short-day than under long-day conditions. VRN3 was revealed as an epigenetic regulation point integrating vernalization and day length signals. We globally identified genes maintaining vernalization-induced epigenetic changes. Most of these genes showed dose-dependent vernalization responses, revealing a quantitative 'recording system' for vernalization. Our studies shed light on the epigenetic role of VRN3 and H3K4me3/H3K27me3 in vernalization and reveal genes underlying epigenetic memory, laying the foundation for further study.