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Light is one of the environmental signals that regulate the development of shoot architecture. Molecular mechanisms regulating shoot branching by light signals have not been investigated in detail. Analyses of light signaling mutants defective in branching provide insight into the molecular events associated with the phenomenon. It is well documented that phytochrome B (phyB) mutant plants display constitutive shade avoidance responses, including increased plant height and enhanced apical dominance. We investigated the phyB-1 mutant sorghum (Sorghum bicolor) and analyzed the expression of the sorghum Teosinte Branched1 gene (SbTB1), which encodes a putative transcription factor that suppresses bud outgrowth, and the sorghum dormancy-associated gene (SbDRM1), a marker of bud dormancy. Buds are formed in the leaf axils of phyB-1; however, they enter into dormancy soon after their formation. The dormant state of phyB-1 buds is confirmed by the high level of expression of the SbDRM1 gene. The level of SbTB1 mRNA is higher in the buds of phyB-1 compared to wild type, suggesting that phyB mediates the growth of axillary shoots in response to light signals in part by regulating the mRNA abundance of SbTB1. These results are confirmed by growing wild-type seedlings with supplemental far-red light that induces shade avoidance responses. We hypothesize that active phyB (Pfr) suppresses the expression of the SbTB1 gene, thereby inducing bud outgrowth, whereas environmental conditions that inactivate phyB allow increased expression of SbTB1, thereby suppressing bud outgrowth.

Black pericarp sorghum has notable value due to the biosynthesis of 3-deoxyanthocyanidins (3-DOAs), a rare class of bioactive polyphenols valued as antioxidant food additives and as bioactive compounds with cytotoxicity to human cancer cells. A metabolic and transcriptomic study was conducted to ascertain the cellular events leading to the activation of 3-DOA biosynthesis in black sorghum pericarp. Prolonged exposure of pericarp during grain maturation to high-fluence ultraviolet (UV) light resulted in elevated levels of reactive oxygen species (ROS) and the activation of 3-DOA biosynthesis in pericarp tissues. In conjunction with 3-DOA biosynthesis was the transcriptional activation of specific family members of early and late flavonoid biosynthesis pathway genes as well as the downstream activation of defense-related pathways. Promoter analysis of genes highly correlated with 3-DOA biosynthesis in black pericarp were enriched in MYB and HHO5/ARR-B motifs. Light microscopy studies of black pericarp tissues suggest that 3-DOAs are predominantly localized in the epicarp and are associated with the cell wall. A working model of UV-induced 3-DOA biosynthesis in black pericarp is proposed that shares features of plant immunity associated with pathogen attack or mechanical wounding. The present model depicts ROS accumulation, the transcriptional activation of receptor kinases and transcription factors (TFs) including NAC, WRKY, bHLH, AP2, and C2H2 Zinc finger domain. This study identified key biosynthetic and regulatory genes of 3-DOA accumulation in black pericarp and provided a deeper understanding of the gene networks and cellular events controlling this tissue-and genotype-specific trait.

Biofuels produced from non-food lignocellulosic feedstocks have the potential to replace a significant percentage of fossil fuels via high yield potential and suitability for cultivation on marginal lands. Commercialization of dedicated lignocellulosic crops into single biofuels, however, is hampered by conversion technology costs and decreasing oil prices. Integrated biorefinery approaches, where value-added chemicals are produced in conjunction with biofuels, offer significant potential towards overcoming this economic disadvantage. In this study, candidate lignocellulosic feedstocks were evaluated for their potential biomass and silica yields. Feedstock entries included pearl millet-napiergrass (“PMN”; Pennisetum glaucum [L.] R. Br. × P. purpureum Schumach.), napiergrass (P. purpureum Schumach.), annual sorghum (Sorghum bicolor [L.] Moench), pearl millet (P. glaucum [L.] R. Br.), perennial sorghum (Sorghum spp.), switchgrass (Panicum virgatum L.), sunn hemp (Crotalaria juncea L.), giant miscanthus (Miscanthus × giganteus J.M. Greef and Deuter), and energy cane (Saccharum spp.). Replicated plots were planted at three locations and characterized for biomass yield, chemical composition including hemicellulose, cellulose, acid detergent lignin (ADL), neutral detergent fiber (NDF), crude protein (CP), and silica concentration. The PMN, napiergrass, energy cane, and sunn hemp had the highest biomass yields. They were superior candidates for ethanol production due to high cellulose and hemicellulose content. They also had high silica yield except for sunn hemp. Silica yield among feedstock entries ranged from 41 to 3249 kg ha−1. Based on high bioethanol and biosilica yield potential, PMN, napiergrass, and energy cane are the most promising biorefinery feedstock candidates for improving biofuel profitability.

While rhizome formation is intimately associated with perennialism and the derived benefit of sustainability, the introduction of this trait into temperate-zone adapted Sorghum cultivars requires precise knowledge of the genetics conditioning this trait in order to minimize the risk of weediness (e.g., Johnsongrass, S. halepense) while maximizing the productivity of perennial sorghum. As an incremental step towards dissecting the genetics of perennialism, a segregating F4 heterogeneous inbred family derived from a cross between S. bicolor and S. propinquum was phenotyped in both field and greenhouse environments for traits related to over-wintering and rhizome formation. An unseasonably cold winter in 2011 provided high selection pressure, and hence 74.8 % of the population did not survive. This severe selection pressure for cold tolerance allowed the resolution of two previously unidentified over-wintering quantitative trait locus (QTL) and more powerful correlation models than previously reported. Conflicting with previous reports, a maximum of 33 % of over-wintering variation could be explained by above-ground shoot formation from rhizomes; however, every over-wintering plant exhibited rhizome growth. Thus, while rhizome formation is required for over-wintering, other factors also determine survival in this interspecific population. The fine mapping of a previously reported rhizome QTL on sorghum chromosome SBI-01 was conducted by targeting this genomic region with additional simple sequence repeat markers. Fine mapping reduced the 2-LOD rhizome QTL interval from ~59 to ~14.5 Mb, which represents a 75 % reduction in physical distance and a 53 % reduction in the number of putative genes in the locus.

Asexual reproduction through seeds, or apomixis, is a process that holds much promise for agricultural advances. However, the molecular mechanisms underlying apomixis are currently poorly understood. To identify genes related to female gametophyte development in apomictic ovaries of buffelgrass (Pennisetum ciliare (L.) Link), Suppression Subtractive Hybridization of ovary cDNA with leaf cDNA was performed. Through macroarray screening of subtracted cDNAs two genes were identified, Pca21 and Pca24, that showed differential expression between apomictic and sexual ovaries. Sequence analysis showed that both Pca21 and Pca24 are novel genes not previously characterized in plants. Pca21 shows homology to two wheat genes that are also expressed during reproductive development. Pca24 has similarity to coiled-coil-helix-coiled-coil-helix (CHCH) domain containing proteins from maize and sugarcane. Northern blot analysis revealed that both of these genes are expressed throughout female gametophyte development in apomictic ovaries. In situ hybridizations localized the transcript of these two genes to the developing embryo sacs in the apomictic ovaries. Based on the expression patterns it was concluded that Pca21 and Pca24 likely play a role during apomictic development in buffelgrass.

Sorghum [Sorghum bicolor (L.) Moench] breeders have long recognized the importance of exotic germplasm and noncultivated sorghum races as sources of valuable genes for genetic improvement. The genus Sorghum consists of 25 species classified as five sections: Eu-sorghum, Chaetosorghum, Heterosorghum, Para-sorghum, and Stiposorghum Species outside the Eu-sorghum section are sources of important genes for sorghum improvement, including those for insect and disease resistance, but these have not been used because of the failure of these species to cross with sorghum. An understanding of the biological nature of the incompatibility system(s) that prevent hybridization and/or seed development is necessary for the successful hybridization and introgression between sorghum and divergent Sorghum species. The objectives of this study were to determine the reason(s) for reproductive isolation between Sorghum species. The current study utilized 14 alien Sorghum species and established that pollen–pistil incompatibilities are the primary reasons that hybrids with sorghum are not obtained. The alien pollen tubes showed major inhibition of growth in sorghum pistils and seldom grew beyond the stigma. Pollen tubes of only three species grew into the ovary of sorghum. Fertilization and subsequent embryo development were not common. Seeds with developing embryos aborted before maturation, apparently because of breakdown of the endosperm.

The fraction of photosynthetically active radiation a canopy intercepts (fiPAR) drives canopy level photosynthesis. There is currently no universal, repeatable fiPAR sensor deployment method. We show variability of fiPAR measurements by three sensor deployment methods, including two 1 by 1 m and one 3 by 1 m method. The deployment method biased measurements (P = 0.005) under buffelgrass (Pennisetum ciliare L) canopies. These effects were less evident in ‘Alamo’ switchgrass (Panicum virgatum L) and miscanthus (Miscanthus x giganteus). Canopies of these two species showed deployment method x nutrient addition interaction effects (P = 0.02), apparently driven by nutrient effects on leaf area index (LAI). We highlight potential implications of using the different deployment methods via an exercise in the application of Beer's law. As actual LAI increased, effect of deployment method on fiPAR measurements tended to diminish, suggesting in high LAI systems a universal deployment method is not as critical as it is in low LAI systems.

Hybridization within sorghum [Sorghum bicolor (L.) Moench] has been the primary means of creating genetic diversity for improvement. While considerable variation exists within S. bicolor, traits such as biotic stress tolerance could be improved if secondary and tertiary germplasm pools were accessible through hybridization. Sorghum germplasm possessing the inhibition of alien pollen (iap) allele has enhanced the ability to make successful wide hybridizations between secondary and tertiary gene pools. However, the range of this efficacy has not been tested. Pollen from Miscanthus Andersson, Pennisetum Rich., Sorghastrum Nash, and Zea L. was transferred to the stigmas of S. bicolor lines Tx3361 (with the iap allele) and ATx623 (without the iap allele). Pollen of all genera exhibited tube growth, but the frequencies of germination and growth rates varied among species and accessions within a genus. Significantly more pollen germinated and grew into the pistils of Tx3361 than ATx623. Pollen grains were noticeably more numerous on stigmas of Tx3361, implying that factors within Tx3361 may also affect pollen adhesion. The results indicate that the potential for intergeneric hybridization of S. bicolor via Tx3361 will vary based on the individual species and accessions within a species that are used as pollinators.

St. Augustinegrass is one of the most important warm season turfgrasses in the southern United States because of its shade tolerance. Most cultivars are diploids (2n = 2x = 18) and are susceptible to various diseases and insects. Polyploid cultivars in the species have some resistance to pests, but most lack cold tolerance. In this study, eight polyploid genotypes were crossed with six diploid cultivars to transfer pest resistance to the diploids. Because interploid crosses often result in aborted seed, it was necessary to use in vitro techniques. Using embryo rescue, 268 plants were recovered from 2,463 emasculated and pollinated florets (10.88% crossability). Because of the heterogeneous nature of the species, these purported hybrids could not be verified by phenotype. DNA markers were used for hybrid identification. A subset of 25 plants from crosses between the aneuploid cultivar Floratam (2n = 4x = 32) and five diploid cultivars were analyzed using 144 expressed sequence tags-simple sequence repeats (EST-SSRs) developed from buffelgrass cDNA sequence data. Chi-square tests for paternal-specific markers revealed that all analyzed progeny were true F₁ hybrids and none originated from self-fertilization or unintended outcrossing. In addition to identifying DNA polymorphism, the EST-SSRs revealed that genetic variation exists among all analyzed cultivars and is not partitioned between ploidy levels. The findings demonstrate that these embryo rescue techniques will enable the entire spectrum of St. Augustinegrass genetic variation to be better used through the recovery of interploid hybrids.

Wild Australian Sorghum species are a tertiary gene pool to grain sorghum [Sorghum bicolor (L.) Moench], and they are of interest to breeders because of their resistance to important insects and pathogens. However, strong reproductive barriers have prevented hybridization between S. bicolor and these wild species. The purpose of this study was to determine if the recessive iap allele (dominant allele Iap = inhibition of alien pollen) would reduce or eliminate the pollen–pistil incompatibilities that prevent hybridization between S. bicolor and divergent Sorghum species. Cytoplasmic male-sterile S. bicolor plants, homozygous for the iap allele, were pollinated with three divergent Sorghum species, S. angustum Blake, S. nitidum (Vahl) Pers., and S. macrospermum Garber. The pollen of these three wild species readily germinated and the pollen tubes grew to the base of the S. bicolor ovary within 2 h after pollination. Hybrid embryos were detected in the S. bicolor florets 13 to 20 d post-pollination. Sorghum bicolor × S. angustum and S. bicolor × S. nitidum hybrids were obtained using embryo rescue followed by in vitro culture techniques and hybrids between S. bicolor and S. macrospermum were obtained by simply germinating the hybrid seed. These hybrids were confirmed by their morphological and cytological traits. These findings clearly demonstrate that the recessive iap allele circumvents pollen–pistil incompatibilities in the genus Sorghum and permits hybrids to be made between S. bicolor and species of the tertiary gene pool.