INDETERMINATE DOMAIN-DELLA protein interactions orchestrate gibberellin-mediated cell elongation in wheat and barley
DELLA proteins are members of the GRAS-domain family of transcriptional regulators and modulate transcriptional activity through protein-protein interactions with at least 15 different classes of transcription factor. The plant hormone gibberellin (GA) regulates a range of growth and development responses including promoting cell elongation, by triggering the degradation of DELLA proteins. More than 70% of modern wheat (Triticum aestivum L.) varieties carry alleles encoding DELLA proteins that are resistant to GA-mediated degradation. These alleles result in constitutive growth repression in stem tissues and confer a semi-dwarf growth habit associated with improved lodging resistance. However, these alleles also have negative pleiotropic effects such as reduced nitrogen use efficiency and weak early vigour that restrict their utility in some environments. A detailed understanding of the mechanisms by which DELLA proteins regulate growth and development will be necessary to dissect these responses and develop targeted strategies to breed improved crop varieties. We identified the orthologous C2H2 Zinc-finger transcription factors INDETERMINATE DOMAIN 5 (IDD5) in wheat and SEMI-DWARF3 (SDW3) in barley (Hordeum vulgare) as positive regulators of stem and leaf expansion. Both IDD5 and SDW3 physically interact with DELLA proteins and are epistatic to these genes. We propose a mechanism by which IDD proteins integrate GA signals to modulate downstream gene transcriptional activity through a protein complex dual activation and repression activities. Changes in GA biosynthesis gene expression levels suggest that part of this response involves GA homeostasis. Plants carrying null mutations in IDD5 and SDW3 exhibit a GA-insensitive semi-dwarf growth habit comparable to the Rht-D1b 'Green Revolution' allele and have potential as novel dwarfing alleles in cereal breeding programmes. Overall design: RNA-seq was conducted on Cadenza, idd5 and Rht-D1b genotypes. Seven days after sowing, half of the plants were treated with 100 µM GA3 and the other half with water. Eight hours after the treatment leaf sheath tissue between the grain and the top of the coleoptile was harvested and flash-frozen in liquid nitrogen. Four biological replicates for each genotype and treatment were used. The trimmed paired-end reads were mapped to wheat IWGSC RefSeq v2.1 genome assembly. The raw mapped reads were counted and converted to TPM's (transcripts per million). The raw data (.fastq) and TPM values for all expressed genes are included in this submission.