Takakazu Matsuura

Chromosomes responsible for sensitivity of embryo to abscisic acid and dormancy in wheat

The sensitivity of the embryo to abscisic acid (ABA) has been reported toplay an important role in seed dormancy. Using ditelocentric lines of wheatcv. Chinese Spring (CS, nondormant and ABA insensitive), F2 seedsbetween monosomic lines of CS and a wheat line Kitakei-1354 (dormant,ABA sensitive) and deletion lines of CS chromosome 4A, germinability ofseeds and embryo-half seeds incubated in water and ABA were examined. The results indicated that the long arm of chromosome 4A carried majorgene(s) for the embryo sensitivity to ABA and dormancy. Chromosome2D might be also involved in the sensitivity to ABA.

Accumulation and leakage of abscisic acid during embryo development and seed dormancy in wheat

Seed dormancy develops latein embryogenesis after a period of potential prematuregermination and has been associated with levels ofabscisic acid (ABA) in, and sensitivity to, ABA ofembryos. In wheat (Triticum aestivum L.)embryos, there are two peaks in levels of ABA duringdevelopment: the first occurs 25 days afterpollination (DAP) and the second from 35 to 40 DAP. The first peak of ABA appears to be associated withthe development of the embryos sensitivity to ABAsince such sensitivity was altered in seeds on earsthat were incubated in a solution of ABA from 15 and20 DAP. In the embryos of Kitakei wheat, a line thatexhibits dormancy, the second peak, at around 35 DAP,was more prolonged in comparison to Chihoku, anon-dormant line. The results support the proposedinvolvement of ABA in the formation and maintenance ofseed dormancy during middle and late embryogenesis. When developing embryos were incubated in water,embryonic ABA leaked out from the embryos, inparticular between 30 and 40 DAP. Prematuregermination observed between 30 and 40 DAP might berelated to such leakage of ABA from embryos.

Allantoin, a stress-related purine metabolite, can activate jasmonate signaling in a MYC2-regulated and abscisic acid-dependent manner.

Highlight Allantoin, a stress-related purine metabolite, can activate JA responses via ABA in Arabidopsis, suggesting its possible involvement in the homeostasis of these phytohormones and their interplay in stress signaling.

A poly(A)-specific ribonuclease directly regulates the poly(A) status of mitochondrial mRNA in Arabidopsis

Coordination of gene expression in the organelles and the nucleus is important for eukaryotic cell function. Transcriptional and post-transcriptional gene regulation in mitochondria remains incompletely understood in most eukaryotes, including plants. Here we show that poly(A)-specific ribonuclease, which influences the poly(A) status of cytoplasmic mRNA in many eukaryotes, directly regulates the poly(A) tract of mitochondrial mRNA in conjunction with a bacterial-type poly(A) polymerase, AGS1, in Arabidopsis. An Arabidopsis poly(A)-specific ribonuclease-deficient mutant, ahg2-1, accumulates polyadenylated mitochondrial mRNA and shows defects in mitochondrial protein complex levels. Mutations of AGS1 suppress the ahg2-1 phenotype. Mitochondrial localizations of AHG2 and AGS1 are required for their functions in the regulation of the poly(A) tract of mitochondrial mRNA. Our findings suggest that AHG2 and AGS1 constitute a regulatory system that controls mitochondrial mRNA poly(A) status in Arabidopsis.

ABI1 regulates carbon/nitrogen-nutrient signal transduction independent of ABA biosynthesis and canonical ABA signalling pathways in Arabidopsis

Highlight ABI1 was identified as the corresponding gene of the C/N-nutrient response mutant cni2-D. This study provides a new insight into the cross-talk between C/N and ABA signalling under the control of ABI1.

Ozone-Induced Rice Grain Yield Loss Is Triggered via a Change in Panicle Morphology That Is Controlled by ABERRANT PANICLE ORGANIZATION 1 Gene

Rice grain yield is predicted to decrease in the future because of an increase in tropospheric ozone concentration. However, the underlying mechanisms are unclear. Here, we investigated the responses to ozone of two rice (Oryza Sativa L.) cultivars, Sasanishiki and Habataki. Sasanishiki showed ozone-induced leaf injury, but no grain yield loss. By contrast, Habataki showed grain yield loss with minimal leaf injury. A QTL associated with grain yield loss caused by ozone was identified in Sasanishiki/Habataki chromosome segment substitution lines and included the ABERRANT PANICLE ORGANIZATION 1 (APO1) gene. The Habataki allele of the APO1 locus in a near-isogenic line also resulted in grain yield loss upon ozone exposure, suggesting APO1 involvement in ozone-induced yield loss. Only a few differences in the APO1 amino acid sequences were detected between the cultivars, but the APO1 transcript level was oppositely regulated by ozone exposure: i.e., it increased in Sasanishiki and decreased in Habataki. Interestingly, the levels of some phytohormones (jasmonic acid, jasmonoyl-L-isoleucine, and abscisic acid) known to be involved in attenuation of ozone-induced leaf injury tended to decrease in Sasanishiki but to increase in Habataki upon ozone exposure. These data indicate that ozone-induced grain yield loss in Habataki is caused by a reduction in the APO1 transcript level through an increase in the levels of phytohormones that reduce leaf damage.

Comprehensive quantification and genome survey reveal the presence of novel phytohormone action modes in red seaweeds

Emerging work has suggested the existence of phytohormones in seaweeds, although chemical species, endogenous biosynthetic pathways, and signal transduction machineries remain poorly understood. We performed profiling of nine phytohormones with liquid chromatography-mass spectrometry and in silico genome-wide homology search to identify genes involved in biosynthesis and signal transduction of hormones in red algae. It was demonstrated that two Bangiophycean algae, Bangia fuscopurpurea and Pyropia yezoensis, possessed indoleacetic acid (IAA), N6-(Δ2-isopentenyl)adenine (iP), abscisic acid (ABA), and salicylic acid, although trans-zeatin, dihydrozeatin, gibberellin A1 and A4, and jasmonate were not detected. Results of genome-wide survey demonstrated that Bangiophycean algae produce iP and ABA via pathways similar to those in terrestrial plants. However, these seaweeds lack homologues of already known factors participating in perception and signal transduction of IAA, iP, ABA and SA, indicating that the action modes of these phytohormones in red seaweeds differ from those elucidated in terrestrial plants. These findings shed lights on evolutional divergence of signal transduction pathways of phytohormones in plants.

Identification of quantitative trait locus for abscisic acid responsiveness on chromosome 5A and association with dehydration tolerance in common wheat seedlings

The phytohormone abscisic acid (ABA) plays important roles in response to environmental stress as well as in seed maturation and dormancy. In common wheat, quantitative trait loci (QTLs) for ABA responsiveness at the seedling stage have been reported on chromosomes 1B, 2A, 3A, 6D and 7B. In this study, we identified a novel QTL for ABA responsiveness on chromosome 5A using an F2 population derived from a cross between the common wheat cultivar Chinese Spring (CS) and a chromosome substitution line of CS with chromosome 5A of cultivar Hope (Hope5A). This QTL was found in a similar chromosomal region to previously reported QTLs for drought tolerance and seed dormancy. Physiological characterization of the QTL revealed a small effect on dehydration tolerance and seed dormancy. The rate of water loss from leaves during dehydration was lower, and transcript accumulation of the cold responsive (COR)/late embryogenesis abundant (LEA) genes Wrab18 and Wdhn13 tended to be higher under dehydration stress in F2 individuals carrying the Hope allele of the QTL, which also showed higher ABA responsiveness than the CS allele-carrying individuals. Seed dormancy of individuals carrying the Hope allele also tended to be lower than those carrying the CS allele. Our results suggest that variation in ABA responsiveness among common wheat cultivars is at least partly determined by the 5A QTL, and that this QTL contributes to development of dehydration and preharvest sprouting tolerance.

Global profiling of phytohormone dynamics during combined drought and pathogen stress in Arabidopsis thaliana reveals ABA and JA as major regulators

Global transcriptome studies demonstrated the existence of unique plant responses under combined stress which are otherwise not seen during individual stresses. In order to combat combined stress plants use signaling pathways and ‘cross talk’ mediated by hormones involved in stress and growth related processes. However, interactions among hormones’ pathways in combined stressed plants are not yet known. Here we studied dynamics of different hormones under individual and combined drought and pathogen infection in Arabidopsis thaliana by liquid chromatography-mass spectrometry (LC-MS) based profiling. Our results revealed abscisic acid (ABA) and salicylic acid (SA) as key regulators under individual drought and pathogen stress respectively. Under combined drought and host pathogen stress (DH) we observed non-induced levels of ABA with an upsurge in SA and jasmonic acid (JA) concentrations, underscoring their role in basal tolerance against host pathogen. Under a non-host pathogen interaction with drought (DNH) stressed plants, ABA, SA and JA profiles were similar to those under DH or non-host pathogen alone. We propose that plants use SA/JA dependent signaling during DH stress which antagonize ABA biosynthesis and signaling pathways during early stage of stress. The study provides insights into hormone modulation at different time points during combined stress.

Endogenous hormone levels affect the regeneration ability of callus derived from different organs in barley

Hordeum vulgare (barley) is an important agricultural crop worldwide. A simple and efficient transformation system is needed to analyze the functions of barley genes and generate lines with improved agronomic traits. Currently, Golden Promise and Igri are the most amenable barley cultivars for stable transformation. Here we evaluated the regeneration ratios and endogenous hormone levels of calli derived from various malting barley cultivars, including Golden Promise, Haruna Nijo, and Morex. We harvested samples not only from immature embryos, but also from different explants of juvenile plants, cotyledons, coleoptiles, and roots. The callus properties differed among genotypes and explant types. Calli derived from the immature embryos of Golden Promise, which showed the highest ratio of regeneration of green shoots, had the highest contents of indoleacetic acid, trans-zeatin, and cis-zeatin. By contrast, calli derived from the cotyledons of Morex and the immature embryos of Haruna Nijo had elevated levels of salicylic acid and abscisic acid, respectively. We thus propose that the former phytohormones are positively associated with the regeneration ability of callus but the later phytohormones are negatively associated.