Likun An

Hulless barley is a cold-resistant crop widely planted in the northwest plateau of China. It is also the main food crop in this region. Phosphorus (P), as one of the important essential nutrient elements, regulates plant growth and defense. This study aimed to analyze the development and related molecular mechanisms of hulless barley under P deficiency and explore the regulatory genes so as to provide a basis for subsequent molecular breeding research. Transcriptome analysis was performed on the root and leaf samples of hulless barley cultured with different concentrations of KH₂PO₄ (1 mM and 10 μM) Hoagland solution. A total of 46,439 genes were finally obtained by the combined analysis of leaf and root samples. Among them, 325 and 453 genes had more than twofold differences in expression. These differentially expressed genes (DEGs) mainly participated in the abiotic stress biosynthetic process through Gene Ontology prediction. Moreover, the Kyoto Encyclopedia of Genes and Genomes showed that DEGs were mainly involved in photosynthesis, plant hormone signal transduction, glycolysis, phenylpropanoid biosynthesis, and synthesis of metabolites. These pathways also appeared in other abiotic stresses. Plants initiated multiple hormone synergistic regulatory mechanisms to maintain growth under P-deficient conditions. Transcription factors (TFs) also proved these predictions. The enrichment of ARR-B TFs, which positively regulated the phosphorelay-mediated cytokinin signal transduction, and some other TFs (AP2, GRAS, and ARF) was related to plant hormone regulation. Some DEGs showed different values in their FPKM (fragment per kilobase of transcript per million mapped reads), but the expression trends of genes responding to stress and phosphorylation remained highly consistent. Therefore, in the case of P deficiency, the first response of plants was the expression of stress-related genes. The effects of this stress on plant metabolites need to be further studied to improve the relevant regulatory mechanisms so as to further understand the importance of P in the development and stress resistance of hulless barley.

The APETALA2/Ethylene-Responsive Transcriptional Factors containing conservative AP2/ERF domains constituted a plant-specific transcription factor (TF) superfamily, called AP2/ERF. The configuration of the AP2/ERF superfamily in maize has remained unresolved. In this study, we identified the 229 AP2/ERF genes in the latest (B73 RefGen_v5) maize reference genome. Phylogenetic classification of the ZmAP2/ERF family members categorized it into five clades, including 27 AP2 (APETALA2), 5 RAV (Related to ABI3/VP), 89 DREB (dehydration responsive element binding), 105 ERF (ethylene responsive factors), and a soloist. The duplication events of the paralogous genes occurred from 1.724–25.855 MYA, a key route to maize evolution. Structural analysis reveals that they have more introns and few exons. The results showed that 32 ZmAP2/ERFs regulate biotic stresses, and 24 ZmAP2/ERFs are involved in responses towards abiotic stresses. Additionally, the expression analysis showed that DREB family members are involved in plant sex determination. The real-time quantitative expression profiling of ZmAP2/ERFs in the leaves of the maize inbred line B73 under ABA, JA, salt, drought, heat, and wounding stress revealed their specific expression patterns. Conclusively, this study unveiled the evolutionary pathway of ZmAP2/ERFs and its essential role in stress and developmental processes. The generated information will be useful for stress resilience maize breeding programs.