The Sorghum Photoperiod Sensitivity Gene, Ma3, Encodes a Phytochrome B

Abstract

The Ma, gene is one of six genes that regulate the photoperiodic sensitivity of flowering in sorghum (Sorghum bicolor [L.] Moench).The masR mutation of this gene causes a phenotype that is similar to plants that are known to lack phytochrome B, and masR sorghum lacks a 123-kD phytochrome that predominates in light-grown plants and that is present in non-magR plants. A population segregating for Ma, and masR was created and used to identify two randomly amplified polymorphic DNA markers linked to Ma,. These two markers were cloned and mapped in a recombinant inbred population as restriction fragment length polymorphisms. cDNA clones of PHYA and PHYC were cloned and sequenced from a cDNA library prepared from green sorghum leaves. Using a genome-walking technique, a 7941 -bp partia1 sequence of PHYB was determined from genomic DNA from masR sorghum. PHYA, PHYB, and P H Y C all mapped to the same linkage group. The Ma,-linked markers mapped with PHYB more than 121 centimorgans from PHYA and PHYC. A frameshift mutation resulting in a premature stop codon was found in the PHYB sequence from magR sorghum. Therefore, we conclude that the Ma, locus in sorghum is a PHYB gene that encodes a 123-kD phytochrome.The transition from vegetative to reproductive growth is the result of the activation of genes responsible for inflorescence and floral organ formation. These genes, which control apex identity and floral organ morphogenesis, are strictly regulated, since their improper expression results in abnormal flowers and inflorescences (Okamuro et al., 1993;Veit et al., 1993). The initial activation of these genes is usually the result of environmental cues that indicate an appropriate time to flower. The mechanisms by which environmental factors activate inflorescence and floral organ production are complex and many genes are known to be involved in the transduction of environmental signals that regulate flowering (Bernier et al., 1993; Coupland, 1995).Of all of the environmental factors that are sensed by plants, daylength is probably the most important in inducing flowering. The phenomenon whereby daylength regulates flowering is referred to as photoperiodism. An understanding of the effect of daylength on reproductive development has agronomic importance because the ability to alter flowering time allows the cultivation of a species in environments that differ greatly from the one in which it originally evolved. Our understanding of photoperiodism has historically relied upon a physiological examination of the phenomenon. Recently, genetic analysis of floral induction has provided new insights into this process. In the LD plant Arabidopsis thaliana a series of genes has been recognized that influences flowering time, and these genes have been categorized into six phenotypic groups based on earliness or lateness in flowering in response to short days, long days, and vernalization; (Coupland, 1995). The existence of these separate phenotypic classes suggests the existence of severa1 pathways that regulate photoperiod sens...

Targeted Analysis of Orthologous Phytochrome A Regions of the Sorghum, Maize, and Rice Genomes using Comparative Gene-Island Sequencing

“…A BAC clone (ZmPHYA) containing an 80-kb region of the maize (Zea mays) genome was identified by hybridization with a sorghum PHYA cDNA clone (Childs et al, 1997). A 100-kb BAC clone (OsPHYA) containing the rice (Oryza sativa) PHYA ortholog was similarly identified by screening a rice cv Teqing BAC library (Zhang et al, 1996) with the sorghum PHYA cDNA clone.…”

“…Sorghum BAC sbb3766 was identified by screening an ordered library of 13,440 BAC clones (Woo et al, 1994) with a sorghum PHYA cDNA clone (Childs et al, 1997). The sequence of sorghum BAC sbb3766 consists of 152,439 bp (accession no.…”

“…U56729; Childs et al, 1997). Large-scale isolation of sbb3766 BAC DNA was carried out using the Maxi-prep kit (Qiagen USA, Valencia, CA), according to the instructions provided by the manufacturer for low copy number plasmids.…”

Transcriptome Profiling of Tiller Buds Provides New Insights into PhyB Regulation of Tillering and Indeterminate Growth in Sorghum

“…This set of phenotypes is known as the "shade avoidance syndrome" [(SAS); Smith and Whitelam, 1997)]. PhyB-deficient plants in diverse species constitutively display the SAS (Reed et al, 1993;Childs et al, 1997;Kebrom et al, 2006;Finlayson et al, 2010). The early flowering and stem elongation responses have been investigated in-depth and are mediated in part by changes in the level or action of most of the major plant hormones (Carabelli et al, 1993;Finlayson et al, 1999;Morelli and Ruberti, 2000;Cerdán and Chory, 2003;Carabelli et al, 2007;Sheehan et al, 2007;de Lucas et al, 2008;Kim et al, 2008;Tao et al, 2008).…”

A Photoperiod-Insensitive Barley Line Contains a Light-Labile Phytochrome B1

“…The hy3 mutant in Arabidopsis , the ma 3 R mutant in sorghum (Childs et al, 1992), the ein mutant in Brassica rapa (Devlin et al, 1992), and the lh mutant in cucumber (Lopez-Juez et al, 1992) all flower early and lack a light-stable phyB protein. In Arabidopsis and sorghum it has been shown that the mutation is located in the PHYB gene Childs et al, 1997). The goal of our study is to establish the nature of the mutation in BMDR-1 and to determine whether the failure to respond to photoperiod might also be due to a lack of a functional phyB.…”