Background: Modification of histone acetylation is a ubiquitous and reversible process in eukaryotes and prokaryotes and plays crucial roles in the regulation of gene expression during plant development and stress responses. Histone acetylation is co-regulated by histone acetyltransferase (HAT) and histone deacetylase (HDAC). HAT plays an essential regulatory role in various growth and development processes by modifying the chromatin structure through interactions with other histone modifications and transcription factors in eukaryotic cells, affecting the transcription of genes. Comprehensive analyses ofHATgenes have been performed inArabidopsis thalianaandOryza sativa. However, little information is available on theHATgenes in foxtail millet (Setaria italica[L.] P.Beauv).Results: In this study, 24HATgenes (SiHATs) were identified and divided into four groups with conserved gene structures via motif composition analysis. Phylogenetic analysis of the genes was performed to predict functional similarities betweenArabidopsis thaliana,Oryza sativa, and foxtail millet; 19 and 2 orthologous gene pairs were individually identified. Moreover, all identifiedHATgene pairs likely underwent purified selection based on their non-synonymous/synonymous nucleotide substitutions. Using published transcriptome data, we found thatSiHATgenes were preferentially expressed in some tissues and organs. Stress responses were also examined, and data showed thatSiHATgene transcription was influenced by drought, salt, low nitrogen, and low phosphorus stress, and that the expression of fourSiHATs was altered as a result of infection bySclerospora graminicola.Conclusions: Results indicated that histone acetylation may play an important role in plant growth and development and stress adaptations. These findings suggest thatSiHATsplay specific roles in the response to abiotic stress and viral infection. This study lays a foundation for further analysis of the biological functions ofSiHATsin foxtail millet.

Foxtail millet is a plant that is highly drought-resistant and rich in nutrients. Its grain structure traits are linked with water uptake during grain germination, which is closely related to plant density for high yield under rain fed regions; however, there is no related research. Using Micro-CT technology, we investigated a total of 15 internal structure traits of foxtail millet grains, such as the volume and surface area of the embryo, endosperm, cavity, hull, and whole grain, and mapped relevant quantitative trait loci (QTLs) using recombination inbred lines (RILs). With phenotypic variations in these traits and genome sequences of 100 foxtail millet RILs, four QTLs were identified. In combination with transcriptome profiling during grain development, we identified seven candidate genes that may play a role in the regulation of grain structure in foxtail millet.

The SCARECROW (SCR) transcription factor governs cell-type patterning in plant roots and Kranz anatomy of leaves, serving as a master regulator of root and shoot morphogenesis. Foxtail millet (Setaria italica), characterized by a compact genome, self-pollination, and a short growth cycle, has emerged as a C₄ model plant. Here, we revealed two SCR paralogs in foxtail millet—SiSCR1 and SiSCR2—which exhibit high sequence conservation with ZmSCR1/1h (Zea mays), OsSCR1/2 (Oryza sativa), and AtSCR (Arabidopsis thaliana), particularly within the C-terminal GRAS domain. Both SiSCR genes exhibited nearly identical secondary structures and physicochemical profiles, with promoter analyses revealing five conserved cis-regulatory elements. Robust phylogenetic reconstruction resolved SCR orthologs into monocot- and dicot-specific clades, with SiSCR genes forming a sister branch to SvSCR from its progenitor species Setaria viridis. Spatiotemporal expression profiling demonstrated ubiquitous SiSCR gene transcription across developmental stages, with notable enrichment in germinated seeds, plants at the one-tip-two-leaf stage, leaf 1 (two days after heading), and roots during the seedling stage. Co-expression network analysis revealed that there is a correlation between SiSCR genes and other functional genes. Abscisic acid (ABA) treatment led to a significant downregulation of the expression level of SiSCR genes in Yugu1 roots, and the expression of the SiSCR genes in the roots of An04 is more sensitive to PEG6000 treatment. Drought treatment significantly upregulated SiSCR2 expression in leaves, demonstrating its pivotal role in plant adaptation to abiotic stress. Analysis of heterologous expression under the control of the 35S promoter revealed that SiSCR genes were expressed in root cortical/endodermal initial cells, endodermal cells, cortical cells, and leaf stomatal complexes. Strikingly, ectopic expression of SiSCR genes in Arabidopsis led to hypersensitivity to ABA, and ABA treatment resulted in a significant reduction in the length of the meristematic zone. These data delineate the functional divergence and evolutionary conservation of SiSCR genes, providing critical insights into their roles in root/shoot development and abiotic stress signaling in foxtail millet.

Efficient and fast water uptake by seeds, facilitated by optimal soil moisture, plays a critical role in timely germination and early seedling vigor for foxtail millet production in arid and semi-arid regions. The husk, as a unique structure through which the seed contacts the soil, plays an important role in water uptake and germination. Many foxtail millet germplasm accessions have papillae on the epidermis of their husks, yet the role of this trait in water uptake and germination, as well as the genetic basis and regulatory mechanism related to this trait, remain unknown. In this study, we demonstrated that the water uptake by the seeds from accessions with papillae was significantly higher than that of accessions without papillae two hours and four hours after sowing during a 10 h experiment, resulting in faster germination. Analysis of segregating ratios from two F2 populations derived from crossing between accessions with and without papillae indicated that husk papilla density was of monogenic dominance. Bulked Segregant Analysis Sequencing (BSA-Seq) showed that candidate regions on chromosome 5 were significantly associated with husk papilla density. The mapped region overlapped by the two BSA populations for papilla density included 72 genes. In combination with the expression profiles of these genes, five candidate genes were identified, encoding aquaporins, fructose transporter, and glycoside hydrolase. This study elucidated the role of husk papillae in enhancing water uptake and germination in foxtail millet, provided genetic insights into the trait, and laid the foundation for further study on the mechanism of husk papilla differentiation.