Sweet Sorghum Originated through Selection of Dry, a Plant-Specific NAC Transcription Factor Gene.

Sorghum (Sorghum bicolor) is the fifth most popular crop worldwide and a C4 model plant. Domesticated sorghum comes in many forms, including sweet cultivars with juicy stems and grain sorghum with dry, pithy stems at maturity. The Dry locus, which controls the pithy/juicy stem trait, was discovered over a century ago. Here, we found that Dry gene encodes a plant-specific NAC transcription factor. Dry was either deleted or acquired loss-of-function mutations in sweet sorghum, resulting in cell collapse and altered secondary cell wall composition in the stem. Twenty-three Dry ancestral haplotypes, all with dry, pithy stems, were found among wild sorghum and wild sorghum relatives. Two of the haplotypes were detected in domesticated landraces, with four additional dry haplotypes with juicy stems detected in improved lines. These results imply that selection for Dry gene mutations was a major step leading to the origin of sweet sorghum. The Dry gene is conserved in major cereals; fine-tuning its regulatory network could provide a molecular tool to control crop stem texture.

Sorghum breeding in the genomic era: opportunities and challenges.

KEY MESSAGE: The importance and potential of the multi-purpose crop sorghum in global food security have not yet been fully exploited, and the integration of the state-of-art genomics and high-throughput technologies into breeding practice is required. Sorghum, a historically vital staple food source and currently the fifth most important major cereal, is emerging as a crop with diverse end-uses as food, feed, fuel and forage and a model for functional genetics and genomics of tropical grasses. Rapid development in high-throughput experimental and data processing technologies has significantly speeded up sorghum genomic researches in the past few years. The genomes of three sorghum lines are available, thousands of genetic stocks accessible and various genetic populations, including NAM, MAGIC, and mutagenised populations released. Functional and comparative genomics have elucidated key genetic loci and genes controlling agronomical and adaptive traits. However, the knowledge gained has far away from being translated into real breeding practices. We argue that the way forward is to take a genome-based approach for tailored designing of sorghum as a multi-functional crop combining excellent agricultural traits for various end uses. In this review, we update the new concepts and innovation systems in crop breeding and summarise recent advances in sorghum genomic researches, especially the genome-wide dissection of variations in genes and alleles for agronomically important traits. Future directions and opportunities for sorghum breeding are highlighted to stimulate discussion amongst sorghum academic and industrial communities.

Genomic footprints of sorghum domestication and breeding selection for multiple end uses.

Domestication and diversification have had profound effects on crop genomes. Originating in Africa and subsequently spreading to different continents, sorghum (Sorghum bicolor) has experienced multiple onsets of domestication and intensive breeding selection for various end uses. However, how these processes have shaped sorghum genomes is not fully understood. In the present study, population genomics analyses were performed on a worldwide collection of 445 sorghum accessions, covering wild sorghum and four end-use subpopulations with diverse agronomic traits. Frequent genetic exchanges were found among various subpopulations, and strong selective sweeps affected 14.68% (∼107.5 Mb) of the sorghum genome, including 3649, 4287, and 3888 genes during sorghum domestication, improvement of grain sorghum, and improvement of sweet sorghum, respectively. Eight different models of haplotype changes in domestication genes from wild sorghum to landraces and improved sorghum were observed, and Sh1- and SbTB1-type genes were representative of two prominent models, one of soft selection or multiple origins and one of hard selection or an early single domestication event. We also demonstrated that the Dry gene, which regulates stem juiciness, was unconsciously selected during the improvement of grain sorghum. Taken together, these findings provide new genomic insights into sorghum domestication and breeding selection, and will facilitate further dissection of the domestication and molecular breeding of sorghum.

[Effects of high temperature and hydrogen cyanamide on dormant nectarine's floral bud respiratory metabolism].

Taking 3-year old potted 'Shuguang' nectarine (Prunus persica var. nectariana cv. Shuguang) as test material, this paper studied the effects of high temperature (50 degrees C, HT) and hydrogen cyanamide (HC) on the floral bud respiratory metabolism of the tree during its natural dormancy. Both HT and HC could break the natural dormancy of the tree, and lead to a significant decrease in the respiratory metabolism of floral buds for several hours. The main respiratory pathways, tricarboxylic acid cycle (TCA) and pentose phosphate pathway (PPP), were affected. For the buds not received dormancy-breaking treatments, both the TCA and the PPP decreased, while treating with HT and HC induced a rapid recovery of PPP after the early respiratory attenuation. HT also induced the recovery of TCA, but HC did not show this effect in 96 hours. Therefore, respiratory attenuation and the following PPP activation could be the important part in the floral bud respiratory mechanism of HT- and HC-induced dormancy release.

[Transcriptional levels of AQPs genes in peach floral buds during dormancy].

Taking the floral buds of 10 years old field-cultivated and 3 years old potted nectarine (Prunus persica var. nectarine cv. Shuguang) as test materials, and by the method of real-time quantitative PCR, this paper studied the expressions of the AQPs genes deltaTIP1 and PIP1; 1 during dormancy and dormancy-release (September 15, 2009-January 15, 2010) and the transcriptional levels of the genes under low temperature stress. Within the period of dormancy and dormancy-release, the transcriptional level of PIP1; 1 presented a persistent increasing trend, and the high level expression of PIP1; 1 in January could be related to the efflux of water through cytoplasma membrane and vacuolar membrane, which protected the bud cells from ice crystal injuries. The contents of soluble sugar, soluble protein, and proline in the bud cells all peaked in January, which prevented the excessive water loss from the cells. After 2 weeks of low temperature treatment, the PIP1; 1 had a high level expression, indicating that it was a cold-induced gene. The transcriptional level of deltaTIP1 fluctuated during dormancy, and increased significantly during dormancy-release, which might be induced by the dormancy-release signals in buds and the resumption of plant activity. After 2 weeks of low temperature treatment, the expression level of deltaTIP1 had no increase, indicating that deltaTIP1 was not a cold-induced gene.