Abscisic Acid Regulates Auxin Homeostasis in Rice Root Tips to Promote Root Hair Elongation

Regulatory Mechanism of ABA and ABI3 on Vegetative Development in the Moss Physcomitrella patens

The moss Physcomitrella patens is a model system for studying plant developmental processes. ABSCISIC ACID INSENSITIVE3 (ABI3), a transcription factor of the ABA signaling pathway, plays an important role in plant growth and development in vascular plant. To understand the regulatory mechanism of ABA and PpABI3 on vegetative development in Physcomitrella patens, we applied physiological, cellular, and RNA-seq analyses in wild type (WT) plants and ∆abi3 mutants. During ABA treatment, the growth of gametophytes was inhibited to a lesser extent ∆abi3 plants compared with WT plants. Microscopic observation indicated that the differentiation of caulonemata from chloronemata was accelerated in ∆abi3 plants when compared with WT plants, with or without 10 μM of ABA treatment. Under normal conditions, auxin concentration in ∆abi3 plants was markedly higher than that in WT plants. The auxin induced later differentiation of caulonemata from chloronemata, and the phenotype of ∆abi3 plants was similar to that of WT plants treated with exogenous indole-3-acetic acid (IAA). RNA-seq analysis showed that the PpABI3-regulated genes overlapped with genes regulated by the ABA treatment, and about 78% of auxin-related genes regulated by the ABA treatment overlapped with those regulated by PpABI3. These results suggested that ABA affected vegetative development partly through PpABI3 regulation in P. patens; PpABI3 is a negative regulator of vegetative development in P. patens, and the vegetative development regulation by ABA and PpABI3 might occur by regulating the expression of auxin-related genes. PpABI3 might be associated with cross-talk between ABA and auxin in P. patens.

Early molecular events associated with nitrogen deficiency in rice seedling roots

Nitrogen (N) deficiency is one of the most common problems in rice. The symptoms of N deficiency are well documented, but the underlying molecular mechanisms are largely unknown in rice. Here, we studied the early molecular events associated with N starvation (−N, 1 h), focusing on amino acid analysis and identification of −N-regulated genes in rice roots. Interestingly, levels of glutamine rapidly decreased within 15 min of −N treatment, indicating that part of the N-deficient signals could be mediated by glutamine. Transcriptome analysis revealed that genes involved in metabolism, plant hormone signal transduction (e.g. abscisic acid, auxin, and jasmonate), transporter activity, and oxidative stress responses were rapidly regulated by −N. Some of the −N-regulated genes encode transcription factors, protein kinases and protein phosphatases, which may be involved in the regulation of early −N responses in rice roots. Previously, we used similar approaches to identify glutamine-, glutamate-, and ammonium nitrate-responsive genes. Comparisons of the genes induced by different forms of N with the −N-regulated genes identified here have provided a catalog of potential N regulatory genes for further dissection of the N signaling pathwys in rice.

Mutations in a subfamily of abscisic acid receptor genes promote rice growth and productivity

Abscisic acid (ABA) is a key phytohormone that controls plant growth and stress responses. It is sensed by the pyrabactin resistance 1 (PYR1)/PYR1-like (PYL)/regulatory components of the ABA receptor (RCAR) family of proteins. Here, we utilized CRISPR/Cas9 technology to edit group I (PYL1-PYL6 and PYL12) and group II (PYL7-PYL11 and PYL13) PYL genes in rice. Characterization of the combinatorial mutants suggested that genes in group I have more important roles in stomatal movement, seed dormancy, and growth regulation than those in group II. Among all of the single pyl mutants, only pyl1 and pyl12 exhibited significant defects in seed dormancy. Interestingly, high-order group I mutants, but not any group II mutants, displayed enhanced growth. Among group I mutants, pyl1/4/6 exhibited the best growth and improved grain productivity in natural paddy field conditions, while maintaining nearly normal seed dormancy. Our results suggest that a subfamily of rice PYLs has evolved to have particularly important roles in regulating plant growth and reveal a genetic strategy to improve rice productivity.

Exploration of ABA Responsive miRNAs Reveals a New Hormone Signaling Crosstalk Pathway Regulating Root Growth of Populus euphratica

Abscisic acid (ABA) plays an important role in the regulation of plant adaptation, seed germination, and root development in plants. However, the mechanism of ABA regulation of root development is still poorly understood, especially through the miRNA-mediated pathway. Here, small RNA (sRNA)-seq and degradome-seq were used to analyze the miRNAs’ responsive to ABA in the stems and roots of P. euphratica, a model tree species for abiotic stress-resistance research. In total, 255 unique mature sequences, containing 154 known miRNAs and 101 novel miRNAs were identified, among which 33 miRNAs and 54 miRNAs were responsive to ABA in the roots and stems, respectively. Furthermore, the analysis of these miRNAs and their targets revealed a new hormone signaling crosstalk model of ABA regulation of root growth through miRNA-mediated pathways, such as peu-miR-n68 mediation of the crosstalk between ABA and the brassinosteroid (BR) signaling pathway and peu-miR477b mediation of the crosstalk between ABA and Gibberellic acid (GA) signaling. Taken together, our genome-wide analysis of the miRNAs provides a new insight into the mechanism of ABA regulation of root growth in Populus.

Elucidation and functional characterization of CsPSY and CsUGT promoters in Crocus sativus L

The dried stigmas of Crocus sativus constitute the saffron, which is considered to be the costliest spice of the world. Saffron is valuable for its constituents, which are mainly apocarotenoids. In order to enhance the production of apocarotenoids, it is imperative to understand the regulation of apocarotenoid biosynthetic pathway. In C. sativus, although the pathway has been elucidated, the information regarding the regulation of the pathwaygenes is scanty. During the present investigation, the characterization of promoters regulating the expression of two important genes i.e. CsPSY and CsUGT was performed. We successfully cloned the promoters of both the genes, which were functionally characterized in Crocus sativus and Nicotiana tabaccum. In silico analysis of the promoters demonstrated the presence of several important cis regulatory elements responding tolight, hormonesand interaction with transcription factors (TFs). Further analysis suggested the regulation of CsPSY promoter by Abscisic acid (ABA) and that of CsUGT by Gibberellic acid (GA). In addition, we also observed ABA and GA mediated modulation in the expression of significant TFs and CsPSY and CsUGT transcripts. Overall, the study addresses issues related to regulation of key genes of apocarotenoid pathway in C.sativus.

Genetic Architecture of Nitrogen-Deficiency Tolerance in Wheat Seedlings Based on a Nested Association Mapping (NAM) Population

Genetic divergence for nitrogen utilization in germplasms is important in wheat breeding programs, especially for low nitrogen input management. In this study, a nested association mapping (NAM) population, derived from "Yanzhan 1" (a Chinese domesticated cultivar) crossed with "Hussar" (a British domesticated cultivar) and another three semi-wild wheat varieties, namely, "Cayazheda 29" (Triticum aestivum ssp. tibetanum Shao), "Yunnan" (T. aestivum ssp. yunnanense King), and "Yutian" (T. aestivum petropavloski Udats et Migusch), was used to detect quantitative trait loci (QTLs) for nitrogen utilization at the seedling stage. An integrated genetic map was constructed using 2,059 single nucleotide polymorphism (SNP) markers from a 90 K SNP chip, with a total coverage of 2,355.75 cM and an average marker spacing of 1.13 cM. A total of 67 QTLs for RDW (root dry weight), SDW (shoot dry weight), TDW (total dry weight), and RSDW (root to shoot ratio) were identified under normal nitrogen conditions (N⁺) and nitrogen deficient conditions (N^-). Twenty-three of these QTLs were only detected under N^- conditions. Moreover, 23 favorable QTLs were identified in the domesticated cultivar Yanzhan 1, 15 of which were detected under N⁺ conditions, while only four were detected under N^- conditions. In contrast, the semi-wild cultivars contributed more favorable N^--specific QTLs (eight from Cayazheda 29; nine from Yunnan), which could be further explored for breeding cultivars adapted to nitrogen-deficient conditions. In particular, QRSDW-5A.1 from YN should be further evaluated using high-resolution mapping.