OsBIC1 Directly Interacts with OsCRYs to Regulate Leaf Sheath Length through Mediating GA-Responsive Pathway

BIC2, a Cryptochrome Function Inhibitor, Is Involved in the Regulation of ABA Responses in Arabidopsis

The plant hormone ABA (abscisic acid) is able to regulate plant responses to abiotic stresses via regulating the expression of ABA response genes. BIC1 (Blue-light Inhibitor of Cryptochromes 1) and BIC2 have been identified as the inhibitors of plant cryptochrome functions, and are involved in the regulation of plant development and metabolism in Arabidopsis . In this study, we report the identification of BIC2 as a regulator of ABA responses in Arabidopsis . RT-PCR (Reverse Transcription-Polymerase Chain Reaction) results show that the expression level of BIC1 remained largely unchanged, but that of BIC2 increased significantly in response to ABA treatment. Transfection assays in Arabidopsis protoplasts show that both BIC1 and BIC2 were mainly localized in the nucleus, and were able to activate the expression of the co-transfected reporter gene. Results in seed germination and seedling greening assays show that ABA sensitivity was increased in the transgenic plants overexpressing BIC2, but increased slightly, if any, in the transgenic plants overexpressing BIC1. ABA sensitivity was also increased in the bic2 single mutants in seedling greening assays, but no further increase was observed in the bic1 bic2 double mutants. On the other hand, in root elongation assays, ABA sensitivity was decreased in the transgenic plants overexpressing BIC2, as well as the bic2 single mutants, but no further decrease was observed in the bic1 bic2 double mutants. By using qRT-PCR (quantitative RT-PCR), we further examined how BIC2 may regulate ABA responses in Arabidopsis , and found that inhibition of ABA on the expression of the ABA receptor genes PYL4 (PYR1-Like 4) and PYL5 were decreased, but promotion of ABA on the expression of the protein kinase gene SnRK2.6 (SNF1-Related Protein Kinases 2.6) was enhanced in both the bic1 bic2 double mutants and 35S:BIC2 overexpression transgenic plants. Taken together, our results suggest that BIC2 regulates ABA responses in Arabidopsis possibly by affecting the expression of ABA signaling key regulator genes.

The Roles of Gibberellins in Regulating Leaf Development

Plant growth and development are correlated with many aspects, including phytohormones, which have specific functions. However, the mechanism underlying the process has not been well elucidated. Gibberellins (GAs) play fundamental roles in almost every aspect of plant growth and development, including cell elongation, leaf expansion, leaf senescence, seed germination, and leafy head formation. The central genes involved in GA biosynthesis include GA20 oxidase genes (GA20oxs), GA3oxs, and GA2oxs, which correlate with bioactive GAs. The GA content and GA biosynthesis genes are affected by light, carbon availability, stresses, phytohormone crosstalk, and transcription factors (TFs) as well. However, GA is the main hormone associated with BR, ABA, SA, JA, cytokinin, and auxin, regulating a wide range of growth and developmental processes. DELLA proteins act as plant growth suppressors by inhibiting the elongation and proliferation of cells. GAs induce DELLA repressor protein degradation during the GA biosynthesis process to control several critical developmental processes by interacting with F-box, PIFS, ROS, SCLl3, and other proteins. Bioactive GA levels are inversely related to DELLA proteins, and a lack of DELLA function consequently activates GA responses. In this review, we summarized the diverse roles of GAs in plant development stages, with a focus on GA biosynthesis and signal transduction, to develop new insight and an understanding of the mechanisms underlying plant development.

Characterization and expression analysis of bHLH transcription factors reveal their putative regulatory effects on nectar spur development in Aquilegia species

Nectar spur is a hollow extension of certain flower parts and shows strikingly diverse size and shape in Aquilegia. Nectar spur development is involved in cell division and expansion processes. The basic helix-loop-helix (bHLH) transcription factors (TFs) control a diversity of organ morphogenesis, including cell division and cell expansion processes. However, the role of bHLH genes in nectar spur development in Aquilegia is mainly unknown. We conducted a genome-wide identification of the bHLH gene family in Aquilegia to determine structural characteristics and phylogenetic relationships, and to analyze expression profiles of these genes during the development of nectar spur in spurless and spurred species. A total of 120 AqbHLH genes were identified from the Aquilegia coerulea genome. The phylogenetic tree showed that AqbHLH proteins were divided into 15 subfamilies, among which S7 and S8 subfamilies occurred marked expansion. The AqbHLH genes in the same clade had similar motif composition and gene structure characteristics. Conserved residue analysis indicated nineteen residues with conservation of more than 50% were found in the four conserved regions. In the upstream sequence of AqbHLH genes, the light-responsive element was the most abundant cis-acting element. Eighteen AqbHLH genes showed syntenic relationships, and eight genes from four syntenic pairs underwent tandem duplications. According to the expression profiling analysis by public RNA-Seq data and qRT-PCR results, five AqbHLH genes, including AqbHLH027, AqbHLH046, AqbHLH082, AqbHLH083 and AqbHLH092, were differentially expressed between different tissues in A. coerulea at early developmental stages, as well as between spurless and spurred Aquilegia species. Of them, AqbHLH046 was not only highly expressed in spur compared with blade, but also showed higher expression levels in spurred species than spurless specie, suggesting it plays an essential role in the development of spur by regulating cell division. This study lays a foundation to investigate the function of AqbHLH genes family in nectar spur development, and has potential implications for speciation and genetic breeding in the genus Aquilegia.

Transcriptome of Endophyte-Positive and Endophyte-Free Tall Fescue Under Field Stresses

Tall fescue is one of the primary sources of forage for livestock. It grows well in the marginal soils of the temperate zones. It hosts a fungal endophyte (Epichloë coenophiala), which helps the plants to tolerate abiotic and biotic stresses. The genomic and transcriptomic resources of tall fescue are very limited, due to a complex genetic background and outbreeding modes of pollination. The aim of this study was to identify differentially expressed genes (DEGs) in two tissues (pseudostem and leaf blade) between novel endophyte positive (E+) and endophyte-free (E-) Texoma MaxQ II tall fescue genotypes. Samples were collected at three diurnal time points: morning (7:40-9:00 am), afternoon (1:15-2:15 pm), and evening (4:45-5:45 pm) in the field environment. By exploring the transcriptional landscape via RNA-seq, for the first time, we generated 226,054 and 224,376 transcripts from E+ and E- tall fescue, respectively through de novo assembly. The upregulated transcripts were detected fewer than the downregulated ones in both tissues (S: 803 up and 878 down; L: 783 up and 846 down) under the freezing temperatures (-3.0-0.5°C) in the morning. Gene Ontology enrichment analysis identified 3 out of top 10 significant GO terms only in the morning samples. Metabolic pathway and biosynthesis of secondary metabolite genes showed lowest number of DEGs under morning freezing stress and highest number in evening cold condition. The 1,085 DEGs were only expressed under morning stress condition and, more importantly, the eight candidate orthologous genes of rice identified under morning freezing temperatures, including orthologs of rice phytochrome A, phytochrome C, and ethylene receptor genes, might be the possible route underlying cold tolerance in tall fescue.