The G protein subunit α1, CaGα1, mediates ethylene sensing of mango anthracnose pathogen Colletotrichum asianum to regulate fungal development and virulence and mediates surface sensing for spore germination.

Mango is an important tropic fruit, but its production is highly restricted by anthracnose diseases. Mango anthracnose development is related to the fruit-ripening hormone ethylene, but how the pathogen senses ethylene and affects the infection remains largely unknown. In this study, mango pathogen Colletotrichum asianum strain TYC-2 was shown to sense ethylene to enhance spore germination, appressorium formation and virulence. Upon further analysis of ethylene sensing signaling, three histidine kinase genes (CaHKs) and a G-protein gene (CaGα1) were functionally characterized. Ethylene upregulated the expression of the three CaHKs but had no influence on CaGα1 expression. No function in ethylene sensing was identified for the three CaHKs. Ethylene enhanced spore germination and multiple appressorium formation of the wild-type TYC-2 but not CaGα1 mutants. TYC-2 has extremely low germination in water, where self-inhibition may play a role in ethylene sensing via CaGα1 signaling. Self-inhibitors extracted from TYC-2 inhibited spore germination of TYC-2 and CaGα1 mutants, but ethylene could not rescue the inhibition, indicating that the self-inhibition was not mediated by CaGα1 and had no interactions with ethylene. Interestingly, spore germination of CaGα1 mutants was significantly enhanced in water on hydrophobic but not hydrophilic surfaces, suggesting that CaGα1 is involved in surface sensing. In the pathogenicity assay, CaGα1 mutants showed less virulence with delayed germination and little appressorium formation at early infection on mango leaves and fruit. Transcriptome and qRT-PCR analyses identified several pathogenicity-related genes regulated by ethylene, indicating that ethylene may regulate TYC-2 virulence partially by regulating the expression of these genes.

First report of Septoria blotch of passion fruit caused by Septoria passifloricola in Taiwan.

Passion fruit originated in South America and cultivated in tropical and subtropical countries for the fresh market and juice processing. In Taiwan, healthy grafted seedlings of passion fruit have been used for replanting every year to minimize the impact of viral and root diseases. The grafted seedlings commonly used purple passion fruit 'Tainung NO.1' (Passiflora edulis × Passiflora edulis forma flavicarpa) abbreviated as PPF as scion, and yellow passion fruit (P. edulis f. flavicarpa) abbreviated as YPF as rootstock. In July 2016 and May 2018, a new leaf disease of passion fruit was observed in Taichung City and Nantou County on 2 to 3-month-old grafted passion fruit seedlings. About 17% of seedlings showed symptoms on leaves in a commercial greenhouse nursery. The infected leaves abscised earlier, causing reduced survival of grafted seedlings. The leaf lesions on YPF and PPF were round to irregular and white-grayish or light brown, and were surrounded by dark green borders and obvious chlorotic halos. Fungal pycnidia were formed in the center of lesions, and extruded yellow-white long conidial tendrils under high humidity. The presumed fungal pathogens were obtained by single spore isolation. Six isolates from the two geographic regions with similar morphological characteristics on potato dextrose agar were obtained. To confirm the pathogenicity, YPF seedlings were inoculated by dropping 10 µL of a conidial suspension of isolate PLS-S2 (107 conidia/mL) on each inoculation site located on abaxial leaves surfaces that were either intact or wounded to form 3 pinpricks in a 4 mm area with a sterilized needle. Three plants were used in a treatment and four leaves of each plant were inoculated. The inoculated plants were kept in plastic bags with high humidity for 3 days and grown in a walk-in growth chamber at 24℃ with a 12-h light regime. The initial symptoms were punctate lesions that later enlarged to round, necrotic spots surrounded by yellow halos, which resembled symptoms in commercial greenhouse nurseries. About 44% of inoculation sites (n= 48) on intact leaves developed lesions at 28 days post-inoculation (dpi) while 100% of inoculation sites (n= 72) on wounded leaves showed lesions at 21 dpi. No lesions developed on leaves with water control. Pathogens reisolated from these lesions were morphologically identical to the inoculated fungus. Conidia were hyaline, filiform to cylindrical with 1-3 nonconstricted septa, and mostly 9-30 × 1.0-2.3 µm. The morphological characteristics of the isolates were similar to Septoria passifloricola Punith (Cline, 2006). Molecular identification was based on concatenated sequences of partial TEF1-α gene (accession nos. MK643056 to MK643061) and ß-tubulin gene (accession nos. MK643050 to MK643055) for each of the six isolates. The BLAST search revealed that strain PLS-S2 was 100.0% identical (392 bp) to S. passifloricola CBS 129431 for the TEF1-α gene (KF253443.1) and 98.4% identical (311 bp) for the ß-tubulin gene (KF252964.1). Phylogenetic analysis showed that PLS-S2 and five additional isolates clustered with reference strains of S. passifloricola (Verkley et al. 2013) in a well-supported clade (95% bootstrap value). Results suggested that the leaf disease of passion fruit in Taiwan was caused by S. passifloricola. This disease has been reported in Africa, India, Australia, New Zealand, Caribbean, and South America (Cline 2006; Ploetz et al. 2003). If appropriate control actions are not taken, the disease may become a major leaf disease in nurseries in Taiwan.

Phenolic compositions and antioxidant properties of leaves of eight persimmon varieties harvested in different periods.

The compositions and contents of antioxidant components and antioxidant attributes (scavenging DPPH radicals, TEAC, ferric reducing power and inhibiting Cu2+-induced human LDL oxidation) for the leaves of eight persimmon varieties harvested from Sep. to Nov. were determined. Harvest time and variety were important factors affecting the compositions and contents of phenolic compounds in persimmon leaves; moreover, phenolic contents (polyphenol, flavonoid, condensed tannin and phenolic acid) of the leaves were significantly correlated with their antioxidant activities. For each variety, the leaves harvested in months with higher temperature, solar radiation and sunshine duration had higher phenolic contents contributing to better antioxidant properties (ranking: Sep. > Oct. > Nov.). In addition, the compositions and contents of phenolic components and antioxidant capacities for the leaves from various persimmon varieties were also different. The leaves of persimmon varieties belonging to pollination constant and astringent (PCA) had higher phenolic contents and also presented better antioxidant effects.

Expression Profiles of Phosphoenolpyruvate Carboxylase and Phosphoenolpyruvate Carboxylase Kinase Genes in Phalaenopsis, Implications for Regulating the Performance of Crassulacean Acid Metabolism.

Phalaenopsis is one of the most important potted plants in the ornamental market of the world. Previous reports implied that crassulacean acid metabolism (CAM) orchids at their young seedling stages might perform C3 or weak CAM photosynthetic pathways, but the detailed molecular evidence is still lacking. In this study, we used a key species in white Phalaenopsis breeding line, Phalaenopsis aphrodite subsp. formosana, to study the ontogenetical changes of CAM performance in Phalaenopsis. Based on the investigations of rhythms of day/night CO2 exchange, malate contents and phosphoenolpyruvate carboxylase (PEPC) activities, it is suggested that a progressive shift from C3 to CAM occurred as the protocorms differentiated the first leaf. To understand the role of phosphoenolpyruvate carboxylase kinase (PEPC kinase) in relation to its target PEPC in CAM performance in Phalaenopsis, the expression profiles of the genes encoding PEPC (PPC) and PEPC kinase (PPCK) were measured in different developmental stages. In Phalaenopsis, two PPC isogenes were constitutively expressed over a 24-h cycle similar to the housekeeping genes in all stages, whereas the significant day/night difference in PaPPCK expression corresponds to the day/night fluctuations in PEPC activity and malate level. These results suggest that the PaPPCK gene product is most likely involved in regulation of CAM performance in different developmental stages of Phalaenopsis seedlings.

Re-emergence of Lilium callosum Sieb. et Zucc. in Taiwan after a fire allows propagation and renews the possibility of conservation.

BACKGROUND: Lilium callosum is native to Taiwan, but little is known about it since it has been considered extinct since 1915. After the rediscovery of this rare species after a fire in 2011 in Tunghsiao Township, intensive work has been conducted to count the number in the wild population, to develop a conservation strategy, and to understand its reproductive characteristics and even economic potential. RESULTS: To conserve the germplasm of this population, three scales from a wild L. callosum plant were collected to establish a mass propagation system. Flowers from two regenerated plants were crossed by hand-pollination, the ovules were rescued and cultured in vitro, and 10 offspring were obtained. The karyotype was determined to be 2n = 2x = 24 = 2m + 2m(sat) + 2sm + 8st + 10t. The phylogenetic analysis using ITS sequences revealed that the sample of L. callosum from Taiwan was not grouped with the other accessions of L. callosum from other regions. The native habitat is classified as grass-dominated vegetation at the early successional stage and a subtropical monsoon-type climate. To clarify the causes of population scarcity in the native environment, reproductive characteristics of regenerated plants were investigated. CONCLUSIONS: Based on the information from this study, it is possible that factors intrinsic to L. callosum could combine to limit pollination and seed formation. The L. callosum pollen only germinated at a temperature that was higher than the native environment, the plants are self-incompatibile, there was a and scarce population, scattered flowering time and dichogamy. Through the culture of these wild harvested parts, the diversity of the germplasm has been broadened and is now available to preserve this rare and valuable species for the future.

Mutation of the Arabidopsis NRT1.5 nitrate transporter causes defective root-to-shoot nitrate transport.

Little is known about the molecular and regulatory mechanisms of long-distance nitrate transport in higher plants. NRT1.5 is one of the 53 Arabidopsis thaliana nitrate transporter NRT1 (Peptide Transporter PTR) genes, of which two members, NRT1.1 (CHL1 for Chlorate resistant 1) and NRT1.2, have been shown to be involved in nitrate uptake. Functional analysis of cRNA-injected Xenopus laevis oocytes showed that NRT1.5 is a low-affinity, pH-dependent bidirectional nitrate transporter. Subcellular localization in plant protoplasts and in planta promoter-beta-glucuronidase analysis, as well as in situ hybridization, showed that NRT1.5 is located in the plasma membrane and is expressed in root pericycle cells close to the xylem. Knockdown or knockout mutations of NRT1.5 reduced the amount of nitrate transported from the root to the shoot, suggesting that NRT1.5 participates in root xylem loading of nitrate. However, root-to-shoot nitrate transport was not completely eliminated in the NRT1.5 knockout mutant, and reduction of NRT1.5 in the nrt1.1 background did not affect root-to-shoot nitrate transport. These data suggest that, in addition to that involving NRT1.5, another mechanism is responsible for xylem loading of nitrate. Further analyses of the nrt1.5 mutants revealed a regulatory loop between nitrate and potassium at the xylem transport step.

Mutation of a nitrate transporter, AtNRT1:4, results in a reduced petiole nitrate content and altered leaf development.

Unlike nitrate uptake of plant roots, less is known at the molecular level about how nitrate is distributed in various plant tissues. In the present study, characterization of the nitrate transporter, AtNRT1:4, revealed a special role of petiole in nitrate homeostasis. Electrophysiological studies using Xenopus oocytes showed that AtNRT1:4 was a low-affinity nitrate transporter. Whole-mount in situ hybridization and RT-PCR demonstrated that AtNRT1:4 was expressed in the leaf petiole. In the wild type, the leaf petiole had low nitrate reductase activity, but a high nitrate content, indicating that it is the storage site for nitrate, whereas, in the atnrt1:4 mutant, the petiole nitrate content was reduced to 50-64% of the wild-type level. Moreover, atnrt1:4 mutant leaves were wider than wild-type leaves. This study revealed a critical role of AtNRT1:4 in regulating leaf nitrate homeostasis, and the deficiency of AtNRT1:4 can alter leaf development.