CONSTANS is a photoperiod regulated activator of flowering in sorghum.

Shanshan Yang,Daryl T Morishige,John E Mullet,Brock D Weers

doi:10.1186/1471-2229-14-148

Abstract

BackgroundSorghum genotypes used for grain production in temperate regions are photoperiod insensitive and flower early avoiding adverse environments during the reproductive phase. In contrast, energy sorghum hybrids are highly photoperiod sensitive with extended vegetative phases in long days, resulting in enhanced biomass accumulation. SbPRR37 and SbGHD7 contribute to photoperiod sensitivity in sorghum by repressing expression of SbEHD1 and FT-like genes, thereby delaying flowering in long days with minimal influence in short days (PNAS_108:16469-16474, 2011; Plant Genome_in press, 2014). The GIGANTEA (GI)-CONSTANS (CO)-FLOWERING LOCUS T (FT) pathway regulates flowering time in Arabidopsis and the grasses (J Exp Bot_62:2453-2463, 2011). In long day flowering plants, such as Arabidopsis and barley, CONSTANS activates FT expression and flowering in long days. In rice, a short day flowering plant, Hd1, the ortholog of CONSTANS, activates flowering in short days and represses flowering in long days.ResultsQuantitative trait loci (QTL) that modify flowering time in sorghum were identified by screening Recombinant Inbred Lines (RILs) derived from BTx642 and Tx7000 in long days, short days, and under field conditions. Analysis of the flowering time QTL on SBI-10 revealed that BTx642 encodes a recessive CONSTANS allele containing a His106Tyr substitution in B-box 2 known to inactivate CONSTANS in Arabidopsis thaliana. Genetic analysis characterized sorghum CONSTANS as a floral activator that promotes flowering by inducing the expression of EARLY HEADING DATE 1 (SbEHD1) and sorghum orthologs of the maize FT genes ZCN8 (SbCN8) and ZCN12 (SbCN12). The floral repressor PSEUDORESPONSE REGULATOR PROTEIN 37 (PRR37) inhibits sorghum CONSTANS activity and flowering in long days.ConclusionSorghum CONSTANS is an activator of flowering that is repressed post-transcriptionally in long days by the floral inhibitor PRR37, contributing to photoperiod sensitive flowering in Sorghum bicolor, a short day plant.

Highlights

Sorghum genotypes used for grain production in temperate regions are photoperiod insensitive and flower early avoiding adverse environments during the reproductive phase
Identification of flowering time Quantitative trait loci (QTL) Flowering time QTL were mapped in a Recombinant Inbred Lines (RILs) population derived from a cross of BTx642 and Tx7000, genotypes used in U.S grain sorghum breeding programs as sources of drought tolerance [37]
Flowering time QTL were mapped in this population by phenotyping the RIL population for days to half pollen shed in greenhouses in 14 h long days (LD), 10 h short days (SD), and under field conditions where day length increases following plant emergence in mid-April from 12.6 h to 14.3 h in July

Summary

Introduction

Sorghum genotypes used for grain production in temperate regions are photoperiod insensitive and flower early avoiding adverse environments during the reproductive phase. Energy sorghum hybrids are highly photoperiod sensitive with extended vegetative phases in long days, resulting in enhanced biomass accumulation. SbPRR37 and SbGHD7 contribute to photoperiod sensitivity in sorghum by repressing expression of SbEHD1 and FT-like genes, thereby delaying flowering in long days with minimal influence in short days (PNAS_108:16469-16474, 2011; Plant Genome_in press, 2014). Grain sorghum is generally selected for early flowering (60–80 days) to enhance grain yield stability by avoiding drought, adverse temperatures, and insect pressure during the reproductive phase. Energy sorghum hybrids are designed with high photoperiod sensitivity in order to delay flowering and extend the duration of vegetative growth, resulting in more than 2-fold increases in biomass production [3,4]. The stage of plant development, signals from photoperiod, temperature, gibberellins and other factors are integrated to regulate flowering time in sorghum [5]

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Conclusion