Identification of transcriptional networks controlling leaf sheath growth in Sorghum bicolor.

OBJECTIVES: The objective of this data set was to identify transcriptional networks that control elongation of seedling leaf sheaths in the C4 grass Sorghum bicolor. One motivation was that leaf sheaths are a primary constituent of stems in grass seedlings; therefore, genes that control growth of this organ are important contributors to successful transition from the seedling stage to the mature plant stage and, ultimately, crop success. Since diurnal rhythms contribute to regulation of signaling networks responsible for growth, a time course representing the late afternoon and early evening was anticipated to pinpoint important control genes for stem growth. Ultimately, the expected outcome was discovery of transcript networks that integrate internal and external signals to fine tune leaf sheath growth and, consequently, plant height. DATA DESCRIPTION: The data set is RNAseq profiling of upper leaf sheaths collected from wild type Sorghum bicolor (BTx623 line) plants at four-hour intervals from 12.5 h after dawn to 20 h after dawn. Global transcript levels in leaves were determined by deep sequencing of mRNA from four individual seedlings at each time point. This data set contains sequences representing the spectrum of mRNAs from individual genes. This data set enables detection of significant changes in gene-level expression caused by the progression of the day from late afternoon to the middle of the night. This data set is useful to identify gene expression networks regulating growth in the leaf sheath, an organ that is a major contributor to the sorghum seedling stem and defines seedling height.

Sorghum bicolor INDETERMINATE1 is a conserved primary regulator of flowering.

Introduction: A fundamental developmental switch for plants is transition from vegetative to floral growth, which integrates external and internal signals. INDETERMINATE1 (Id1) family proteins are zinc finger transcription factors that activate flowering in grasses regardless of photoperiod. Mutations in maize Id1 and rice Id1 (RID1) cause very late flowering. RID1 promotes expression of the flowering activator genes Early Heading Date1 (Ehd1) and Heading date 1 (Hd1), a rice homolog of CONSTANS (CO). Methods and results: Mapping of two recessive late flowering mutants from a pedigreed sorghum EMS mutant library identified two distinct mutations in the Sorghum bicolor Id1 (SbId1) homolog, mutant alleles named sbid1-1 and sbid1-2. The weaker sbid1-1 allele caused a 35 day delay in reaching boot stage in the field, but its effect was limited to 6 days under greenhouse conditions. The strong sbid1-2 allele delayed boot stage by more than 60 days in the field and under greenhouse conditions. When sbid1-1 and sbid1-2 were combined, the delayed flowering phenotype remained and resembled that of sbid1-2, confirming late flowering was due to loss of SbId1 function. Evaluation of major flowering time regulatory gene expression in sbid1-2 showed that SbId1 is needed for expression of floral activators, like SbCO and SbCN8, and repressors, like SbPRR37 and SbGhd7. Discussion: These results demonstrate a conserved role for SbId1 in promotion of flowering in sorghum, where it appears to be critical to allow expression of most major flowering regulatory genes.