Genetic Architecture of Novel Sources for Reproductive Cold Tolerance in Sorghum

Reproductive Cold Stress in Contrasting Sorghum Genotypes: Is Pollen Fertility Really the Crucial Trait?

The influence of cold stress during the reproductive phase can lead to substantial yield losses in sorghum. In order to extend cultivation into temperate regions, a better understanding of reproductive cold tolerance is essential for breeding progress. To further elucidate the mechanisms responsible for cold tolerance, a cold-tolerant and a cold-sensitive parental line, along with their reciprocal F1 hybrids, were subjected to cold stress at various stages of reproductive development, with a focus on pollen fertility and receptivity of female floral organs. For this purpose, pollen measurements were conducted using impedance flow cytometry, and the panicle harvest index was determined post-maturation. While existing literature primarily attributes reduced pollen fertility as the cause of decreased seed set, this study provides evidence that female floral organs might be more affected than previously assumed. We found that the onset of generative tissue formation until BBCH39 (flag leaf visible) is the most cold-sensitive developmental stage and that there is no predominance of maternal or paternal effects associated with the inheritance of cold tolerance in reciprocal F1 hybrids. These findings offer valuable insights for the development of cold-tolerant sorghum varieties to enable cultivation in colder regions and enhance yield stability in temperate climates. Further studies should aim at validating and expanding these findings from the limited number of representative genotypes analyzed in the present manuscript to global sorghum diversity.

Transcriptome Analysis Reveals the Pivotal Genes and Regulation Pathways Under Cold Stress and Identifies SbERF027, an AP2/ERF Gene That Confers Cold Tolerance in Sorghum

Low temperature at the seedling stage adversely affects sorghum growth and development and limits its geographical distribution. APETALA2/Ethylene-Responsive transcription factors (AP2/ERFs), one of the largest transcription factor families in plants, play essential roles in growth, development, and responses to abiotic stresses. However, the roles of AP2/ERF genes in cold tolerance in sorghum and the mechanisms underlying their effects remain largely unknown. Here, transcriptome sequencing (RNA-seq) was performed on the leaves of sorghum seedlings before and after cold treatment. Several candidate genes for cold tolerance and regulation pathways involved in "photosynthesis" under cold stress were identified via Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment. Additionally, the AP2/ERF family gene SbERF027, a novel regulator of cold tolerance, was functionally identified through a comprehensive analysis. The expression of SbERF027 was high in seedlings and panicles, and its expression was induced by low temperature; the cold-induced expression level of SbERF027 was markedly higher in cold-tolerant accession SZ7 than in cold-sensitive accession Z-5. SbERF027 was detected in the nucleus under both normal and cold stress conditions. In addition, the cold tolerance of SbERF027-overexpressing lines was higher than that of wild-type plants; while the cold tolerance of lines with SbERF027 silenced via virus-induced gene silencing (VIGS) was significantly lower than that of wild-type plants. Further research demonstrated that SNP-911 of the promoter was essential for enhancing cold tolerance by mediating SbERF027 expression. This study lays a theoretical foundation for dissecting the mechanism of cold tolerance in sorghum and has implications for the breeding and genetic improvement of cold-tolerant sorghum.

Decoding the genetic blueprint: regulation of key agricultural traits in sorghum

Sorghum, the fifth most important crop globally, thrives in challenging environments such as arid, saline-alkaline, and infertile regions. This remarkable crop, one of the earliest crops domesticated by humans, offers high biomass and stress-specific properties that render it suitable for a variety of uses including food, feed, bioenergy, and biomaterials. What's truly exciting is the extensive phenotypic variation in sorghum, particularly in traits related to growth, development, and stress resistance. This inherent adaptability makes sorghum a game-changer in agriculture. However, tapping into sorghum's full potential requires unraveling the complex genetic networks that govern its key agricultural traits. Understanding these genetic mechanisms is paramount for improving traits such as yield, quality, and tolerance to drought and saline-alkaline conditions. This review provides a comprehensive overview of functionally characterized genes and regulatory networks associated with plant and panicle architectures, as well as stress resistance in sorghum. Armed with this knowledge, we can develop more resilient and productive sorghum varieties through cutting-edge breeding techniques like genome-wide selection, gene editing, and synthetic biology. These approaches facilitate the identification and manipulation of specific genes responsible for desirable traits, ultimately enhancing agricultural performance and adaptability in sorghum.

Early exposure to phosphorus starvation induces genetically determined responses in Sorghum bicolor roots

KEY MESSAGE

We identified novel physiological and genetic responses to phosphorus starvation in sorghum diversity lines that augment current knowledge of breeding for climate-smart crops in Europe. Phosphorus (P) deficiency and finite P reserves for fertilizer production pose a threat to future global crop production. Understanding root system architecture (RSA) plasticity is central to breeding for P-efficient crops. Sorghum is regarded as a P-efficient and climate-smart crop with strong adaptability to different climatic regions of the world. Here we investigated early genetic responses of sorghum RSA to P deficiency in order to identified genotypes with interesting root phenotypes and responses under low P. A diverse set of sorghum lines (n = 285) was genotyped using DarTSeq generating 12,472 quality genome wide single-nucleotide polymorphisms. Root phenotyping was conducted in a paper-based hydroponic rhizotron system under controlled greenhouse conditions with low and optimal P nutrition, using 16 RSA traits to describe genetic and phenotypic variability at two time points. Genotypic and phenotypic P-response variations were observed for multiple root traits at 21 and 42 days after germination with high broad sense heritability (0.38-0.76). The classification of traits revealed four distinct sorghum RSA types, with genotypes clustering separately under both low and optimal P conditions, suggesting genetic control of root responses to P availability. Association studies identified quantitative trait loci in chromosomes Sb02, Sb03, Sb04, Sb06 and Sb09 linked with genes potentially involved in P transport and stress responses. The genetic dissection of key factors underlying RSA responses to P deficiency could enable early identification of P-efficient sorghum genotypes. Genotypes with interesting RSA traits for low P environments will be incorporated into current sorghum breeding programs for later growth stages and field-based evaluations.

Physiological and Biochemical Regulation Mechanism of Exogenous Hydrogen Peroxide in Alleviating NaCl Stress Toxicity in Tartary Buckwheat (Fagopyrum tataricum (L.) Gaertn)

We aimed to elucidate the physiological and biochemical mechanism by which exogenous hydrogen peroxide (H2O2) alleviates salt stress toxicity in Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn). Tartary buckwheat "Chuanqiao-2" under 150 mmol·L-1 salt (NaCl) stress was treated with 5 or 10 mmol·L-1 H2O2, and seedling growth, physiology and biochemistry, and related gene expression were studied. Treatment with 5 mmol·L-1 H2O2 significantly increased plant height (PH), fresh and dry weights of shoots (SFWs/SDWs) and roots (RFWs/RDWs), leaf length (LL) and area (LA), and relative water content (LRWC); increased chlorophyll a (Chl a) and b (Chl b) contents; improved fluorescence parameters; enhanced antioxidant enzyme activity and content; and reduced malondialdehyde (MDA) content. Expressions of all stress-related and enzyme-related genes were up-regulated. The F3'H gene (flavonoid synthesis pathway) exhibited similar up-regulation under 10 mmol·L-1 H2O2 treatment. Correlation and principal component analyses showed that 5 mmol·L-1 H2O2 could significantly alleviate the toxic effect of salt stress on Tartary buckwheat. Our results show that exogenous 5 mmol·L-1 H2O2 can alleviate the inhibitory or toxic effects of 150 mmol·L-1 NaCl stress on Tartary buckwheat by promoting growth, enhancing photosynthesis, improving enzymatic reactions, reducing membrane lipid peroxidation, and inducing the expression of related genes.

Genetic and genomic diversity in the sorghum gene bank collection of Uganda

BACKGROUND

The Plant Genetic Resources Centre at the Uganda National Gene Bank houses has over 3000 genetically diverse landraces and wild relatives of Sorghum bicolor accessions. This genetic diversity resource is untapped, under-utilized, and has not been systematically incorporated into sorghum breeding programs. In this study, we characterized the germplasm collection using whole-genome SNP markers (DArTseq). Discriminant analysis of principal components (DAPC) was implemented to study the racial ancestry of the accessions in comparison to a global sorghum diversity set and characterize the sub-groups present in the Ugandan (UG) germplasm.

RESULTS

Population structure and phylogenetic analysis revealed the presence of five subgroups among the Ugandan accessions. The samples from the highlands of the southwestern region were genetically distinct as compared to the rest of the population. This subset was predominated by the caudatum race and unique in comparison to the other sub-populations. In this study, we detected QTL for juvenile cold tolerance by genome-wide association studies (GWAS) resulting in the identification of 4 markers associated (-log10p > 3) to survival under cold stress under both field and climate chamber conditions, located on 3 chromosomes (02, 06, 09). To our best knowledge, the QTL on Sb09 with the strongest association was discovered for the first time.

CONCLUSION

This study demonstrates how genebank genomics can potentially facilitate effective and efficient usage of valuable, untapped germplasm collections for agronomic trait evaluation and subsequent allele mining. In face of adverse climate change, identification of genomic regions potentially involved in the adaptation of Ugandan sorghum accessions to cooler climatic conditions would be of interest for the expansion of sorghum production into temperate latitudes.