Analysis the role of arabidopsis <Emphasis Type="Italic">CKRC6/ASA1</Emphasis> in auxin and cytokinin biosynthesis

The crosstalk between auxin and cytokinin (CK) is important for plant growth and development, although the underlying molecular mechanisms remain unclear. Here, we describe the isolation and characterization of a mutant of Arabidopsis Cytokinin-induced Root Curling 6 (CKRC6), an allele of ANTHRANILATE SYNTHASE ALPHA SUBUNIT 1 (ASA1) that encodes the á-subunit of AS in tryptophan (Trp) biosynthesis. The ckrc6 mutant exhibits root gravitropic defects and insensitivity to both CK and the ethylene precursor 1-aminocyclopropane-1-carboxylicacid (ACC) in primary root growth. These defects can be rescued by exogenous indole-3-acetic acid (IAA) or tryptophan (Trp) supplementation. Furthermore, our results suggest that the ckrc6 mutant has decreased IAA content, differential expression patterns of auxin biosynthesis genes and CK biosynthesis isopentenyl transferase (IPT) genes in comparison to wild type. Collectively, our study shows that auxin controls CK biosynthesis based on that CK sensitivity is altered in most auxin-resistant mutants and that CKs promote auxin biosynthesis but inhibit auxin transport and response. Our results also suggest that CKRC6/ASA1 may be located at an intersection of auxin, CK and ethylene metabolism and/or signaling.     

Jasmonic acid modulates xylem development by controlling polar auxin transport in vascular tissues

Development of xylem cells is affected by environmental stresses such as drought and oxidative stress, and recent findings suggested that jasmonic acid (JA) mediates this process through interaction with other phytohormones such as cytokinin. In this study, we showed that polar auxin transport regulated by PIN3 and PIN7 is involved in the JA-mediated xylem development in vascular tissues. The mutant plants that lack the activity of PIN3 and PIN7 responsible for the auxin transport developed extra xylems in vascular tissues such as the JA-treated wild-type plants. Visualization of auxin response and xylem development in the roots treated with NPA, an inhibitor of polar auxin transport, suggested that disruption of polar auxin transport is involved in the xylem phenotype of pin3 pin7 double mutants. We also found that cytokinin increases expressions of PIN3 and PIN7 responsible for the auxin transport while JA decreases only PIN7. These suggested that PIN7-mediated polar auxin transport system modulates xylem development in response to JA. The finding that JA affects auxin distribution in root vascular tissues further supported this. Collectively, these suggest that JA promotes xylem development by disrupting auxin transport in vascular tissues, and the auxin efflux genes, more especially PIN7 whose expression is suppressed by JA mediates this process.     

Reduction of soil-borne pathogen <Emphasis Type="Italic">Fusarium solani</Emphasis> reproduction in soil enriched with phenolic acids by inoculation of endophytic fungus <Emphasis Type="Italic">Phomopsis liquidambari</Emphasis>

The increase of soil-borne pathogens induced by phenolic acids that accumulate in continuous cropping soil reduces the yield and quality of crops. The aims of this study were to investigate (i) the biological control of Fusarium solani, in soil enriched with phenolic acids, by the inoculation of the endophytic fungus Phomopsis liquidambari, and (ii) the biocontrol mechanisms involved. Inoculation of P. liquidambari significantly inhibited the reproduction of F. solani. The prompt degradation of soil phenolic acids by P. liquidambari was determined, but no direct antagonism relationship was observed between P. liquidambari and F. solani, implying the alleviated stimulation of phenolic acids was a major factor in controlling F. solani. Moreover, the presence of glucose did not significantly impact the biocontrol function of P. liquidambari, and P. liquidambari inoculation significantly alleviated disease severity of peanut. Therefore, P. liquidambari could be an effective means to control F. solani in phenolic acids-rich continuous cropping soils.     

Expression of <Emphasis Type="Italic">IPT</Emphasis> in Asakura-sanshoo (<Emphasis Type="Italic">Zanthoxylum piperitum</Emphasis> (L.) DC. f. <Emphasis Type="Italic">inerme</Emphasis> Makino) Alters Tree Architecture,Delays Leaf Senescence,and Changes Leaf Essential Oil Composition

The IPT gene encodes isopentenyl pyrophosphate transferase, a key enzyme in cytokinin biosynthesis. We introduced IPT under the control of the CaMV35S promoter into Asakura-sanshoo (Zanthoxylum piperitum (L.) DC. f. inerme Makino) via stable Agrobacterium tumefaciens-mediated transformation. Three of 3-year-old transgenic Asakura-sanshoo lines Y5, Y16, and Y17 were used to evaluate the effects of IPT expression on the morphological characteristics, leaf senescence, and essential oil composition. Introduced IPT into Asakura-sanshoo stimulated an increase in cytokinin content and a decrease in auxin level. The increase in the cytokinin/auxin ratio affected the tree architecture in 3-year-old transgenic lines. The phenotypes of transgenic lines included reduced stem elongation, decreased leaf surface area, increased branching, and delayed leaf senescence. The expression of IPT in Asakura-sanshoo also affected the leaf essential oil composition. The amount of oxygenated sesquiterpenoid compounds in Y5 and Y16 was 21.1 and 15.8 % higher, respectively, than that in wild type (WT). The amount of aromatic compounds in Y5 and Y16 was 2.9 and 24.6 % lower, respectively, than that in WT. These results show that ipt expression in Asakura-sanshoo conferred desirable traits, including a dwarf growth habit, delayed senescence, and increased concentrations of some sesquiterpenoid compounds.     

Lima bean nodulates efficiently with <Emphasis Type="Italic">Bradyrhizobium</Emphasis> strains isolated from diverse legume species

Lima bean (Phaseolus lunatus L.) is an important legume species that establishes symbiosis with rhizobia, mainly of the Bradyrhizobium genus. The aim of this study was to evaluate the efficiency of rhizobia of the genus Bradyrhizobium in symbiosis with lima bean, in both Leonard jars and in pots with a Latossolo Amarelo distrófico (Oxisol). In the experiment in Leonard jars, 17 strains isolated from nodules of the three legume subfamilies, Papilionoideae (Vigna unguiculata, Pterocarpus sp., Macroptilium atropurpureum, Swartzia sp., and Glycine max), Mimosoideae (Inga sp.), and Caesalpinioideae (Campsiandra surinamensis) and two uninoculated controls, one with a low concentration (5.25 mg L^?1) and another with a high concentration (52.5 mg L^?1) of mineral nitrogen (N) were evaluated. The six strains that exhibited the highest efficiency in Leonard jars, isolated from nodules of Vigna unguiculata (UFLA 03–144, UFLA 03–84, and UFLA 03–150), Campsiandra surinamensis (INPA 104A), Inga sp. (INPA 54B), and Swartzia sp. (INPA 86A), were compared to two uninoculated controls, one without and another with 300 mg N dm^?3 (NH₄NO₃) applied to pots with samples of an Oxisol in the presence and absence of liming. In this experiment, liming did not affect nodulation and plant growth; the INPA 54B and INPA 86A strains stood out in terms of shoot dry matter production and provided increases of approximately 48% in shoot N accumulation compared to the native rhizobia populations. Our study is the first to indicate Bradyrhizobium strains isolated from the three legume subfamilies are able to promote lima bean growth via biological nitrogen fixation in soil conditions.     

<Emphasis Type="Italic">Gr</Emphasis> and <Emphasis Type="Italic">hp</Emphasis>-<Emphasis Type="Italic">1</Emphasis> tomato mutants unveil unprecedented interactions between arbuscular mycorrhizal symbiosis and fruit ripening

Main conclusion

Systemic responses to an arbuscular mycorrhizal fungus reveal opposite phenological patterns in two tomato ripening mutants depending whether ethylene or light reception is involved. The availability of tomato ripening mutants has revealed many aspects of the genetics behind fleshy fruit ripening, plant hormones and light signal reception. Since previous analyses revealed that arbuscular mycorrhizal symbiosis influences tomato berry ripening, we wanted to test the hypothesis that an interplay might occur between root symbiosis and fruit ripening. With this aim, we screened seven tomato mutants affected in the ripening process for their responsiveness to the arbuscular mycorrhizal fungus Funneliformis mosseae. Following their phenological responses we selected two mutants for a deeper analysis: Green ripe (Gr), deficient in fruit ethylene perception and high-pigment-1 (hp-1), displaying enhanced light signal perception throughout the plant. We investigated the putative interactions between ripening processes, mycorrhizal establishment and systemic effects using biochemical and gene expression tools. Our experiments showed that both mutants, notwithstanding a normal mycorrhizal phenotype at root level, exhibit altered arbuscule functionality. Furthermore, in contrast to wild type, mycorrhization did not lead to a higher phosphate concentration in berries of both mutants. These results suggest that the mutations considered interfere with arbuscular mycorrhiza inducing systemic changes in plant phenology and fruits metabolism. We hypothesize a cross talk mechanism between AM and ripening processes that involves genes related to ethylene and light signaling.

     

Antifungal and phytostimulating characteristics of <Emphasis Type="Italic">Bacillus subtilis</Emphasis> Ch-13 rhizospheric strain,producer of bioprepations

Bacillus subtilis Ch-13 industrial strain was shown to have a wide spectrum of antagonistic activities against different species of phytopathogenic fungi and bacteria. The B. subtilis Ch-13 strain produces lytic enzymes; cyanide and other antifungal metabolites; stimulates plant growth, producing phytohormones—auxin derivatives. This strain by 2.5 times reduced the quantity of tomato plants infected with phytopathogenic fungus Fusarium oxysporum during inoculation. Fungi abundance on roots with bacterial inoculation was 6.9 times less than in the absence of inoculation. The application of detected antifungal metabolites as biochemical markers for the strain enables to control the stability of physiologic and biochemical characteristics of the producer, and ensures a rapid quality assay of biopreparations with high performance liquid chromatography (HPLC).     

Different response of an elite <Emphasis Type="Italic">Bt</Emphasis> restorer line of hybrid rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) in adaptation to nitrogen deficiency

Transgenic Bacillus thuringiensis (Bt) rice have been reported to acquire effective resistance against the target pests; however, the insertion and expression of alien Bt genes may have some unintended effects on the growth characteristics of rice. A screen-house experiment was conducted and repeated twice to investigate the growth characteristics and Bt protein expressions in two Bt rice lines [MH63 (Cry2A*) and MH63 (Cry1Ab/Ac)], which had different Bt protein expression levels in leaves, under zero nitrogen (N0) and recommended nitrogen (NR) fertilizer applications. Compared to the counterpart MH63, MH63 (Cry2A*) under N0 experienced accelerated leaf senescence and a lower internal N use efficiency (IE_N), resulting in a 23.2% decrease in grain yield and a lower accumulated biomass. These variations were revealed to be correlated to the higher ratio of the Bt protein content to the soluble protein content (BTC/SPC) with a maximum value of 4.3‰ in MH63 (Cry2A*) leaves in the late growth stage. Under NR, no differences in growth characteristics between MH63 (Cry2A*) and MH63 were found. The growth characteristics of MH63 (Cry1Ab/Ac), with a lower BTC/SPC in the late growth stage compared to MH63 (Cry2A*), were identical to those of MH63 under the two N applications. Results show that the transgenic Bt rice MH63 (Cry2A*), with a relatively higher Bt protein expression in the late growth stage, had an inferior adaptation to nitrogen deficiency compared to its non-Bt counterpart. And this inferior adaptation was found to be correlated with the higher BTC/SPC in MH63 (Cry2A*) leaves in the late growth stage.     

Constitutive expression of the <Emphasis Type="Italic">tzs</Emphasis> gene from <Emphasis Type="Italic">Agrobacterium tumefaciens virG</Emphasis> mutant strains is responsible for improved transgenic plant regeneration in cotton meristem transformation

Key message

virG mutant strains of a nopaline type of Agrobacterium tumefaciens increase the transformation frequency in cotton meristem transformation. Constitutive cytokinin expression from the tzs gene in the virG mutant strains is responsible for the improvement.

Abstract

Strains of Agrobacterium tumefaciens were tested for their ability to improve cotton meristem transformation frequency. Two disarmed A. tumefaciens nopaline strains with either a virGN54D constitutively active mutation or virGI77V hypersensitive induction mutation significantly increased the transformation frequency in a cotton meristem transformation system. The virG mutant strains resulted in greener explants after three days of co-culture in the presence of light, which could be attributed to a cytokinin effect of the mutants. A tzs knockout strain of virGI77V mutant showed more elongated, less green explants and decreased cotton transformation frequency, as compared to a wild type parental strain, suggesting that expression of the tzs gene is required for transformation frequency improvement in cotton meristem transformation. In vitro cytokinin levels in culture media were tenfold higher in the virGN54D strain, and approximately 30-fold higher in the virGI77V strain, in the absence of acetosyringone induction, compared to the wild type strain. The cytokinin level in the virGN54D strain is further increased upon acetosyringone induction, while the cytokinin level in the virGI77V mutant is decreased by induction, suggesting that different tzs gene expression regulation mechanisms are present in the two virG mutant strains. Based on these data, we suggest that the increased cytokinin levels play a major role in increasing Agrobacterium attachment and stimulating localized division of the attached plant cells.