Roles of glycine betaine and proline in improving plant abiotic stress resistance

The flavonoid biosynthetic pathway in Arabidopsis: Structural and genetic diversity

Legumes are highly important food, feed and biofuel crops. With few exceptions, they can enter into an intricate symbiotic relationship with specific soil bacteria called rhizobia. This interaction results in the formation of a new root organ called the nodule in which the rhizobia convert atmospheric nitrogen gas into forms of nitrogen that are useable by the plant. The plant tightly controls the number of nodules it forms, via a complex root-to-shoot-to-root signaling loop called autoregulation of nodulation (AON). This regulatory process involves peptide hormones, receptor kinases and small metabolites. Using modern genetic and genomic techniques, many of the components required for nodule formation and AON have now been isolated. This review addresses these recent findings, presents detailed models of the nodulation and AON processes, and identifies gaps in our understanding of these process that have yet to be fully explained.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1744-7909.2010.00899.x

Molecular Analysis of Legume Nodule Development and Autoregulation

Proliferating cell nuclear antigen (PCNA): a key factor in DNA replication and cell cycle regulation.

https://web.nmsu.edu/~plantgen/supplemental_reading_files/j.1744-7909.2010.00899.x.pdf

Invited Expert Review Molecular Analysis of Legume Nodule Development and Autoregulation

Recently, heavy ions or ion beams have been used to generate new mutants or varieties, especially in higher plants. It has been found that ion beams show high relative biological effectiveness (RBE) of growth inhibition, lethality, and so on, but the characteristics of ion beams on mutation have not been clearly elucidated. To understand the effect of ion beams on mutation induction, mutation rates were investigated using visible known Arabidopsis mutant phenotypes, indicating that mutation frequencies induced by carbon ions were 20-fold higher than by electrons. In chrysanthemum and carnation, flower-color and flower-form mutants, which are hardly produced by gamma rays or X rays, were induced by ion beams. Novel mutants and their responsible genes, such as UV-B resistant, serrated petals and sepals, anthocyaninless, etc. were induced by ion beams. These results indicated that the characteristics of ion beams for mutation induction are high mutation frequency and broad mutation spectrum and therefore, efficient induction of novel mutants. On the other hand, PCR and sequencing analyses showed that half of all mutants induced by ion beams possessed large DNA alterations, while the rest had point-like mutations. Both mutations induced by ion beams had a common feature that deletion of several bases were predominantly induced. It is plausible that ion beams induce a limited amount of large and irreparable DNA damage, resulting in production of a null mutation that shows a new mutant phenotype.

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Studies on Biological Effects of Ion Beams on Lethality, Molecular Nature of Mutation, Mutation Rate, and Spectrum of Mutation Phenotype for Mutation Breeding in Higher Plants

p-Chlorophenoxyisobutyric acid (PCIB) is known as a putative antiauxin and is widely used to inhibit auxin action, although the mechanism of PCIB-mediated inhibition of auxin action is not characterized very well at the molecular level. In the present work, we showed that PCIB inhibited BA::β-glucuronidase (GUS) expression induced by indole-3-acetic acid (IAA), 2,4-dichlorophenoxyacetic acid, and 1-naphthaleneacetic acid. PCIB also inhibited auxin-dependent DR5::GUS expression. RNA hybridization and quantitative reverse transcriptase-polymerase chain reaction analyses suggested that PCIB reduced auxin-induced accumulation of transcripts of Aux/IAA genes. In addition, PCIB relieved the reduction of GUS activity in HS::AXR3NT-GUS transgenic line in which auxin inhibits GUS activity by promoting degradation of the AXR3NT-GUS fusion protein. Physiological analysis revealed that PCIB inhibited lateral root production, gravitropic response of roots, and growth of primary roots. These results suggest that PCIB impairs auxin-signaling pathway by regulating Aux/IAA protein stability and thereby affects the auxin-regulated Arabidopsis root physiology.

p-Chlorophenoxyisobutyric Acid Impairs Auxin Response in Arabidopsis Root

Legume plants tightly control the development and number of symbiotic root nodules. In Lotus japonicus, this regulation requires HAR1 (a CLAVATA1-like receptor kinase) in the shoots, suggesting that a long-distance communication between the shoots and the roots may exist. To better understand its molecular basis, we isolated and characterized a novel hypernodulating mutant of L. japonicus named too much love (tml). Compared with the wild type, tml mutants produced much more nodules which densely covered a wider range of the roots. Reciprocal grafting showed that tml hypernodulation is determined by the root genotype. Moreover, grafting a har1 shoot onto a tml rootstock did not exhibit any obvious additive effects on the nodule number, which was further supported by double mutational analysis. These observations indicate that a shoot factor HAR1 and a root factor TML participate in the same genetic pathway which governs the long-distance signaling of nodule number control. We also showed that the inhibitory effect of TML on nodulation is likely to be local. Therefore, TML may function downstream of HAR1 and the gene product TML might serve as a receptor or mediator of unknown mobile signal molecules that are transported from the shoots to the roots.

https://apsjournals.apsnet.org/doi/pdf/10.1094/MPMI-22-3-0259

Too much love, a root regulator associated with the long-distance control of nodulation in Lotus japonicus.

Summary
We have isolated and characterized a new ultraviolet B (UV-B)-resistant mutant, uvi4 (UV-B-insensitive 4), of Arabidopsis. The fresh weight (FW) of uvi4 plants grown under supplemental UV-B light was more than twice that of the wild-type. No significant difference was found in their ability to repair the UV-B-induced cyclobutane pyrimidine dimers, or in the amount of UV-B absorptive compounds, both of which are well-known factors that contribute to UV sensitivity. Positional cloning revealed that the UVI4 gene encodes a novel basic protein of unknown function. We found that the hypocotyl cells in uvi4 undergo one extra round of endo-reduplication. The uvi4 mutation also promoted the progression of endo-reduplication during leaf development. The UVI4 gene is expressed mainly in actively dividing cells. In the leaves of PUVI4::GUS plants, the GUS signal disappeared in basipetal fashion as the leaf developed. The total leaf blade area was not different between uvi4 and the wild-type through leaf development, while the average cell area in the adaxial epidermis was considerably larger in uvi4, suggesting that the uvi4 leaves have fewer but larger epidermal cells. These results suggest that UVI4 is necessary for the maintenance of the mitotic state, and the loss of UVI4 function stimulated endo-reduplication. Tetraploid Arabidopsis was hyper-resistant to UV-B compared to diploid Arabidopsis, suggesting that the enhanced polyploidization is responsible for the increased UV-B tolerance of the uvi4 mutant.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-313X.2006.02696.x

A mutation in the uvi4 gene promotes progression of endo‐reduplication and confers increased tolerance towards ultraviolet B light

We investigated the usefulness of ion beams for mutation breeding in rice (Oryza sativa L.) by comparing the efficiency (i.e., the ratio of desirable mutations to plant damage such as lethality and sterility), mutation rate, spectrum, and optimum dose to that of gamma rays. Rice seeds were irradiated with carbon ions (mean linear energy transfer = 76 and 107 keV/μm), helium ions (9 keV/μm), and gamma rays, and their survival and fertility were examined in the M1 generation. The frequency of chlorophyll mutations and their types (albina, xantha, and viridis) were examined in the M2 generation, using the M1-plant progeny method. The efficiency of ion beams either equaled or exceeded that of gamma rays. In addition, the mutation rate of ion beams was higher than that of gamma rays. Thus, ion beams appeared to efficiently induce mutants with little radiation damage. No remarkable difference was observed in the relative frequencies of each type of mutation among 3 types of ion beams and gamma rays, thus suggesting that there was no difference in the spectrum. A shoulder dose, which hardly affected survival, was sufficient to efficiently obtain mutants for both types of radiation.

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Atsushi Tanaka

Papers

Studies on Biological Effects of Ion Beams on Lethality, Molecular Nature of Mutation, Mutation Rate, and Spectrum of Mutation Phenotype for Mutation Breeding in Higher Plants

p-Chlorophenoxyisobutyric Acid Impairs Auxin Response in Arabidopsis Root

Too much love, a root regulator associated with the long-distance control of nodulation in Lotus japonicus.

A mutation in the uvi4 gene promotes progression of endo‐reduplication and confers increased tolerance towards ultraviolet B light

Mutagenic effects of ion beam irradiation on rice