Brassinosteroid signaling positively regulates abscisic acid biosynthesis in response to chilling stress in tomato.

Brassinosteroids (BRs) and abscisic acid (ABA) are essential regulators of plant growth and stress tolerance. Although the antagonistic interaction of BRs and ABA is proposed to ensure the balance between growth and defense in model plants, the crosstalk between BRs and ABA in response to chilling in tomato (Solanum lycopersicum), a warm-climate horticultural crop, is unclear. Here, we determined that overexpression of the BR biosynthesis gene DWARF (DWF) or the key BR signaling gene BRASSINAZOLE-RESISTANT1 (BZR1) increases ABA levels in response to chilling stress via positively regulating the expression of the ABA biosynthesis gene 9-CIS-EPOXYCAROTENOID DIOXYGENASE1 (NCED1). BR-induced chilling tolerance was mostly dependent on ABA biosynthesis. Chilling stress or high BR levels decreased the abundance of BRASSINOSTEROID-INSENSITIVE2 (BIN2), a negative regulator of BR signaling. Moreover, we observed that chilling stress increases BR levels and results in the accumulation of BZR1. BIN2 negatively regulated both the accumulation of BZR1 protein and chilling tolerance by suppressing ABA biosynthesis. Our results demonstrate that BR signaling positively regulates chilling tolerance via ABA biosynthesis in tomato. The study has implications in production of warm-climate crops in horticulture.

Rht23 (5Dq') likely encodes a Q homeologue with pleiotropic effects on plant height and spike compactness.

The domesticated gene Q on wheat chromosome 5A (5AQ) encodes an AP2 transcription factor. The 5AQ was originated from a G to A mutation in exon 8 and/or C to T transition in exon 10 and resulted in free-threshing and subcompact spike characters of bread wheat. The Q homeoalleles on 5B and 5D are either a pseudogene or expressed at a low level. Our previous study identified a mutant, named NAUH164, by EMS treatment of wheat variety Sumai 3. The mutant exhibits compact spike and dwarfness, and the mutated locus Rht23 was mapped to the distal of the long arm of chromosome 5D, where 5Dq was located. To investigate the relationship of Rht23 and 5Dq, sequences and expression patterns of 5Dq from Sumai 3 and NAUH164 were compared. The two genotypes had a G3147A single nucleotide polymorphism (SNP), which was predicted to be located within the miR172 binding site of 5Dq. Based on this SNP, an SNP marker was developed and linkage analysis using a (NAUH164 × Alondra's) RIL population showed the marker was co-segregated with the Rht23 mutant traits. The qRT-PCR and Northern blot showed that in NAUH164, the expression of 5Dq was significantly up-regulated, and consistently, the expression of Ta-miR172 was down-regulated in leaves, stems and spikes. Our results demonstrated that point mutation in the miR172 binding site of the 5Dq likely increased its transcript level via a reduction in miRNA-dependent degradation, and this resulted in pleiotropic effects on spike compactness and plant dwarfness.