Arabidopsis Brassinosteroid-overproducing gulliver3-D/dwarf4-D mutants exhibit altered responses to Jasmonic acid and pathogen

Key message

Arabidopsis gulliver3 - D/dwarf4 - D displays growth-promoting phenotypes due to activation tagging of a key brassinosteroid biosynthetic gene DWARF4. In gul3-D/dwf4-D , the Jasmonate and Salicylate signaling pathways were relatively activated and suppressed, respectively.

Abstract

Energy allocation between growth and defense is elegantly balanced to achieve optimal development in plants. Brassinosteroids (BRs), steroidal hormones essential for plant growth, are regulated by other plant hormones, including auxin and jasmonates (JA); auxin stimulates the expression of a key brassinosteroid (BR) biosynthetic gene, DWARF4 (DWF4), whereas JA represses it. To better understand the interaction mechanisms between growth and defense, we isolated a fast-growing mutant, gulliver3-D (gul3-D), that resulted from the activation tagging of DWF4, and examined the response of this mutant to defense signals, including JA, Pseudomonas syringae pv. tomato (Pst DC3000) infection, and wounding. The degree of root growth inhibition following MeJA treatment was significantly decreased in gul3-1D/dwf4-5D relative to the wild type, suggesting that JA signaling is partially desensitized in gul3-1D. Quantitative RT-PCR analysis of the genes involved in JA and salicylic acid (SA) responses, including MYC2, PDF1.2, CORI3, PR1, and PR2, revealed that JA signaling was preferentially activated in gul3-1D, whereas SA signaling was suppressed. As a result, gul3-1D was more susceptible to a biotrophic pathogen, Pst DC3000. Based on our results, we propose a model in which BR and JA cooperate to balance energy allocation between growth and defense responses. In ambient conditions, BRs promote plant growth; however, when stresses trigger JA signaling, JA compromises BR signaling by downregulating DWF4 expression.     

Ectopic expression of a novel Ser/Thr protein kinase from cotton (Gossypium barbadense), enhances resistance to Verticillium dahliae infection and oxidative stress in Arabidopsis

Key message

Overexpression of a cotton defense-related gene GbSTK in Arabidopsis resulted in enhancing pathogen infection and oxidative stress by activating multiple defense-signaling pathways.

Abstract

Serine/threonine protein kinase (STK) plays an important role in the plant stress-signaling transduction pathway via phosphorylation. Most studies about STK genes have been conducted with model species. However, their molecular and biochemical characterizations have not been thoroughly investigated in cotton. Here, we focused on one such member, GbSTK. RT-PCR indicated that it is induced not only by Verticillium dahliae Kleb., but also by signaling molecules. Subcellular localization showed that GbSTK is present in the cell membrane, cytoplasm, and nucleus. Overexpression of GbSTK in Arabidopsis resulted into the enhanced resistance to V. dahliae. Moreover, Overexpression of GbSTK elevated the expression of PR4, PR5, and EREBP, conferring on transgenic plants enhanced reactive oxygen species scavenging capacity and oxidative stress tolerance. Our results suggest that GbSTK is active in multiple defense-signaling pathways, including those involved in responses to pathogen infection and oxidative stress.     

Mono- and digalactosyldiacylglycerols: potent nitric oxide inhibitors from the marine microalga Nannochloropsis granulata

Chemical investigation of a marine microalga, Nannochloropsis granulata, led to the isolation of four digalactosyldiacylglycerols namely, (2S)-1-O-eicosapentaenoyl-2-O-palmitoyl-3-O-(β-d-galactopyranosyl-6-1α-d-galactopyranosyl)-glycerol (1), (2S)-1-O-eicosapentaenoyl-2-O-palmitoleoyl-3-O-(β-d-galactopyranosyl-6-1α-d-galactopyranosyl)-glycerol (2), (2S)-1-O-eicosapentaenoyl-2-O-myristoyl-3-O-(β-d-galactopyranosyl-6-1α-d-galactopyranosyl)-glycerol (3), and (2S)-1,2-bis-O-eicosapentaenoyl-3-O-(β-d-galactopyranosyl-6-1α-d-galactopyranosyl)-glycerol (4), together with their monogalactosyl analogs (5–8). Among the isolated galactolipids 2 and 3 were new natural products. Complete stereochemistry of 1, 4, 5, 7, and 8 was determined for the first time by both spectroscopic techniques and classical degradation methods. Both mono- and digalactosyldiacylglycerols isolated from N. granulata possessed strong nitric oxide (NO) inhibitory activity against lipopolysaccharide-induced NO production in RAW264.7 macrophage cells through downregulation of inducible nitric oxide synthase expression indicating the possible use as anti-inflammatory agents.     

Cloning of seed dormancy genes (TaSdr) associated with tolerance to pre-harvest sprouting in common wheat and development of a functional marker

Key message

After cloning and mapping of wheat TaSdr genes, both the functional markers for TaSdr - B1 and TaVp - 1B were validated, and the distribution of allelic variations at TaSdr - B1 locus in the wheat cultivars from 19 countries was characterized.

Abstract

Seed dormancy is a major factor associated with pre-harvest sprouting (PHS) in common wheat (Triticum aestivum L.). Wheat TaSdr genes, orthologs of OsSdr4 conferring seed dormancy in rice, were cloned by a comparative genomics approach. They were located on homoeologous group 2 chromosomes, and designated as TaSdr-A1, TaSdr-B1 and TaSdr-D1, respectively. Sequence analysis of TaSdr-B1 revealed a SNP at the position -11 upstream of the initiation codon, with bases A and G in cultivars with low and high germination indices (GI), respectively. A cleaved amplified polymorphism sequence marker Sdr2B was developed based on the SNP, and subsequently functional analysis of TaSdr-B1 was conducted by association and linkage mapping. A QTL for GI co-segregating with Sdr2B explained 6.4, 7.8 and 8.7 % of the phenotypic variances in a RIL population derived from Yangxiaomai/Zhongyou 9507 grown in Shijiazhuang, Beijing and the averaged data from those environments, respectively. Two sets of Chinese wheat cultivars were used for association mapping, and results indicated that TaSdr-B1 was significantly associated with GI. Analysis of the allelic distribution at the TaSdr-B1 locus showed that the frequencies of TaSdr-B1a associated with a lower GI were high in cultivars from Japan, Australia, Argentina, and the Middle and Lower Yangtze Valley Winter Wheat Region and Southwest Winter Wheat Region in China. This study provides not only a reliable functional marker for molecular-assisted selection of PHS in wheat breeding programs, but also gives novel information for a comprehensive understanding of seed dormancy.     

AtHSP17.8 overexpression in transgenic lettuce gives rise to dehydration and salt stress resistance phenotypes through modulation of ABA-mediated signaling

Key message

Transgenic Arabidopsis and lettuce plants overexpressing AtHSP17.8 showed ABA-hypersensitive but abiotic stress-resistant phenotypes. ABA treatment caused a dramatic induction of early ABA-responsive genes in AtHSP17.8 -overexpressing transgenic lettuce.

Abstract

Plant small heat shock proteins function as chaperones in protein folding. In addition, they are involved in responses to various abiotic stresses, such as dehydration, heat and high salinity in Arabidopsis. However, it remains elusive how they play a role in the abiotic stress responses at the molecular level. In this study, we provide evidence that Arabidopsis HSP17.8 (AtHSP17.8) positively regulates the abiotic stress responses by modulating abscisic acid (ABA) signaling in Arabidopsis, and also in lettuce, a heterologous plant when ectopically expressed. Overexpression of AtHSP17.8 in both Arabidopsis and lettuce leads to hypersensitivity to ABA and enhanced resistance to dehydration and high salinity stresses. Moreover, early ABA-responsive genes, ABI1, ABI5, NCED3, SNF4 and AREB2, were rapidly induced in AtHSP17.8-overexpressing transgenic Arabidopsis and lettuce. Based on these data, we propose that AtHSP17.8 plays a crucial role in abiotic stress responses by positively modulating ABA-mediated signaling in both Arabidopsis and lettuce. Moreover, our results suggest that stress-tolerant lettuce can be engineered using the genetic and molecular resources of Arabidopsis.     

Introduction of chromosome segment carrying the seed storage protein genes from chromosome 1V of Dasypyrum villosum showed positive effect on bread-making quality of common wheat

Key message

Development of wheat- D. villosum 1V#4 translocation lines; physically mapping the Glu - V1 and Gli - V1 / Glu - V3 loci; and assess the effects of the introduced Glu - V1 and Gli - V1 / Glu - V3 on wheat bread-making quality.

Abstract

Glu-V1 and Gli-V1/Glu-V3 loci, located in the chromosome 1V of Dasypyrum villosum, were proved to have positive effects on grain quality. However, there are very few reports about the transfer of the D. villosum-derived seed storage protein genes into wheat background by chromosome manipulation. In the present study, a total of six CS-1V#4 introgression lines with different alien-fragment sizes were developed through ionizing radiation of the mature female gametes of CS––D. villosum 1V#4 disomic addition line and confirmed by cytogenetic analysis. Genomic in situ hybridization (GISH), chromosome C-banding, twelve 1V#4-specific EST–STS markers and seed storage protein analysis enabled the cytological physical mapping of Glu-V1 and Gli-V1/Glu-V3 loci to the region of FL 0.50–1.00 of 1V#4S of D. villosum. The Glu-V1 allele of D. villosum was Glu-V1a and its coded protein was V71 subunit. Quality analysis indicated that Glu-V1a together with Gli-V1/Glu-V3 loci showed a positive effect on protein content, Zeleny sedimentation value and the rheological characteristics of wheat flour dough. In addition, the positive effect could be maintained when specific Glu-V1 and Gli-V1/Glu-V3 loci were transferred to the wheat genetic background as in the case of T1V#4S-6BS·6BL, T1V#4S·1BL and T1V#4S·1DS translocation lines. These results showed that the chromosome segment carrying the Glu-V1 and Gli-V1/Glu-V3 loci in 1V#4S of D. villosum had positive effect on bread-making quality, and the T1V#4S-6BS·6BL and T1V#4S·1BL translocation lines could be useful germplasms for bread wheat improvement. The developed 1V#4S-specific molecular markers could be used to rapidly identify and trace the alien chromatin of 1V#4S in wheat background.     

Overexpression of a novel salt stress-induced glycine-rich protein gene from alfalfa causes salt and ABA sensitivity in Arabidopsis

Key message

We cloned a novel salt stress-induced glycine-rich protein gene ( MsGRP ) from alfalfa. Its overexpression retards seed germination and seedling growth of transgenic Arabidopsis after salt and ABA treatments.

Abstract

Since soil salinity is one of the most significant abiotic stresses, salt tolerance is required to overcome salinity-induced reductions in crop productivity. Many glycine-rich proteins (GRPs) have been implicated in plant responses to environmental stresses, but the function and importance of some GRPs in stress responses remain largely unknown. Here, we report on a novel salt stress-induced GRP gene (MsGRP) that we isolated from alfalfa. Compared with some glycine-rich RNA-binding proteins, MsGRP contains no RNA recognition motifs and localizes in the cell membrane or cell wall according to the subcellular localization result. MsGRP mRNA is induced by salt, abscisic acid (ABA), and drought stresses in alfalfa seedlings, and its overexpression driven by a constitutive cauliflower mosaic virus-35S promoter in Arabidopsis plants confers salinity and ABA sensitivity compared with WT plants. MsGRP retards seed germination and seedling growth of transgenic Arabidopsis plants after salt and ABA treatments, which implies that MsGRP may affect germination and growth through an ABA-dependent regulation pathway. These results provide indirect evidence that MsGRP plays important roles in seed germination and seedling growth of alfalfa under some abiotic stress conditions.     

The Arabidopsis kinesin gene AtKin-1 plays a role in the nuclear division process during megagametogenesis

Key message

Atkin - 1 , the only Kinesin-1 member of Arabidopsis thaliana , plays a role during female gametogenesis through regulation of nuclear division cycles.

Abstract

Kinesins are microtubule-dependent motor proteins found in eukaryotic organisms. They constitute a superfamily that can be further classified into at least 14 families. In the Kinesin-1 family, members from animal and fungi play roles in long-distance transport of organelles and vesicles. Although Kinesin-1-like sequences have been identified in higher plants, little is known about their function in plant cells, other than in a recently identified Kinesin-1-like protein in a rice pollen semi-sterile mutant. In this study, the gene encoding the only Kinesin-1 member in Arabidopsis, AtKin-1 was found to be specifically expressed in ovules and anthers. AtKin-1 loss-of-function mutants showed substantially aborted ovules in siliques, and this finding was supported by complementation testing. Reciprocal crossing between mutant and wild-type plants indicated that a defect in AtKin-1 results in partially aborted megagametophytes, with no observable effects on pollen fertility. Further observation of ovule development in the mutant pistils indicated that the enlargement of the megaspore was blocked and nuclear division arrested at the one-nucleate stage during embryo sac formation. Our data suggest that AtKin-1 plays a role in the nuclear division cycles during megagametogenesis.     

A virus inhibitory protein isolated from Cyamopsis tetragonoloba (L.) Taub. upon induction of systemic antiviral resistance shares partial amino acid sequence homology with a lectin

Key message

Two virus inhibitory proteins were purified from Cyamopsis tetragonoloba , induced to resist virus infections by CIP-29, a systemic resistance inducing protein from Clerodendrum inerme , and characterized. One of them shared homology with a lectin.

Abstract

CIP-29, a known 29 kDa systemic antiviral resistance inducing protein isolated from Clerodendrum inerme, has been used to induce systemic resistance in Cyamopsis tetragonoloba against Sunn-hemp rosette virus (SRV). Paper reports the detection of virus inhibitory activity in induced-resistant leaf sap of C. tetragonoloba, and the purification of two virus inhibitory agents (VIAs) thereof. VIA activity was recorded as a reduction in lesion number of SRV, Tobacco mosaic virus, and Papaya ringspot virus, when they were incubated separately with resistant sap and inoculated onto susceptible C. tetragonoloba, Nicotiana tabacum cv. Xanthi-nc, and Chenopodium quinoa, respectively. The two VIAs were isolated from resistant C. tetragonoloba plant leaves using combinations of column chromatography. Both were basic proteins, and since their M _r was 32 and 62 kDa, these VIAs were called CT-VIA-32 and CT-VIA-62, respectively, on the basis of their molecular mass and the host. CT-VIA-62 displayed better activity, and was thus studied further. It tested positive for a glycoprotein, and was serologically detected only in leaf tissue post-induction. Tryptic peptides generated in-gel, post SDS-PAGE of CT-VIA-62, were sequenced through LC/MS/MS. All CT-VIA-62 peptides were found to share homologies with proteins from Medicago truncatula that possess a mannose-binding lectin domain.