Conservation and Diversity in Gibberellin-Mediated Transcriptional Responses Among Host Plants Forming Distinct Arbuscular Mycorrhizal Morphotypes

Morphotypes of arbuscular mycorrhizal (AM) symbiosis, Arum, Paris, and Intermediate types, are mainly determined by host plant lineages. It was reported that the phytohormone gibberellin (GA) inhibits the establishment of Arum-type AM symbiosis in legume plants. In contrast, we previously reported that GA promotes the establishment of Paris-type AM symbiosis in Eustoma grandiflorum, while suppressing Arum-type AM symbiosis in a legume model plant, Lotus japonicus. This raises a hitherto unexplored possibility that GA-mediated transcriptional reprogramming during AM symbiosis is different among plant lineages as the AM morphotypes are distinct. Here, our comparative transcriptomics revealed that several symbiosis-related genes were commonly upregulated upon AM fungal colonization in L. japonicus (Arum-type), Daucus carota (Intermediate-type), and E. grandiflorum (Paris-type). Despite of the similarities, the fungal colonization levels and the expression of symbiosis-related genes were suppressed in L. japonicus and D. carota but were promoted in E. grandiflorum in the presence of GA. Moreover, exogenous GA inhibited the expression of genes involved in biosynthetic process of the pre-symbiotic signal component, strigolactone, which resulted in the reduction of its endogenous accumulation in L. japonicus and E. grandiflorum. Additionally, differential regulation of genes involved in sugar metabolism suggested that disaccharides metabolized in AM roots would be different between L. japonicus and D. carota/E. grandiflorum. Therefore, this study uncovered the conserved transcriptional responses during mycorrhization regardless of the distinct AM morphotype. Meanwhile, we also found diverse responses to GA among phylogenetically distant AM host plants.

First Report of Berkeleyomyces basicola Causing Black Root Rot on Lisianthus (Eustoma grandiflorum) in China

Lisianthus (Eustoma grandiflorum (Raf.) Shinn.) is an important ornamental plant ranking in the top 10 cut flowers worldwide (Xiao et al., 2018). In 2020 and 2021, black root rot was found as a major disease limiting lisianthus production in Yunnan Province, China. Black root rot was first observed in early July 2020 on lisianthus grown in a commercial flower-production plantation, with nearly 60% plants infected. Symptoms appeared as coalescing necrotic lesions leading to black discoloration of the roots. Root damage induced by disease resulted in insufficient water and nutrient uptake by the plant, causing stunting and whole-plant wilting. The pathogen could not infect the intact endodermis, and vascular tissues below the discolored cortical tissue remained healthy. Symptomatic roots were surface sterilized using 1% NaClO for 1 min, rinsed three times in sterile water, placed onto potato dextrose agar (PDA), and incubated at 25°C for 7 days in the dark. The morphological characteristics were basically consistent: the colonies were white to gray in color, and the conidiophores were colorless to brown, solitary or clustered. Conidia were single-celled, colorless, rod-shaped, and obtuse at both ends. Chlamydospores were dark brown, clustered or solitary. The morphological characteristics of the pathogen were similar to those of Berkeleyomyces basicola (Berk. & Broome) W.J. Nel, Z.W. de Beer, T.A. Duong & M.J. Wingf. (Nakane et al. 2019). DNA was extracted from mycelia of representative isolate TB using the Plant Genomic DNA Kit (Tiangen, Beijing, China). The internal transcribed spacers (ITS), DNA replication licensing factor (MCM7), ribosomal large subunit (LSU), and 60S ribosomal protein RPL10 (60S) regions were amplified with primer pairs ITS1/ITS4 (Groenewald et al. 2013), MCM7-for/MCM7-rev, LR0R/LR5, and 60S-506F/60S-908R, respectively (Nel et al. 2018). Phylogenetic analysis of multiple genes (Bakhshi et al. 2018) was conducted with the maximum likelihood method using MEGA7. The sequences of our isolate (TB) and three published sequences of B. basicola were clustered into one clade with a 100% bootstrapping value. The accession numbers of B. basicola reference sequences are MF952423 (ITS), MF967079 (MCM7), MF948658 (LSU), and MF967072 (60S) of isolate CMW6714; MF952428 (ITS), MF967088 (MCM7), MF948661 (LSU), and MF967073 (60S) of isolate CMW25440; MF952429 (ITS), MF967102 (MCM7), MF948659 (LSU), and MF967075 (60S) of isolate CMW49352. The sequences of TB have been deposited in GenBank with accession numbers MZ351733 for ITS, MZ695817 for MCM7, MZ695816 for LSU, and MZ695815 for the 60S region. To verify the pathogenicity of the fungus, inoculations were performed on ten 2-month-old potted lisianthus plants by dipping the roots into a conidial suspension (105 spores/ml) for 2 h. Ten plants were mock inoculated with distilled water as a control. Symptoms of black root rot were observed 30 days after inoculation, whereas the control roots remained healthy. The causal fungus has a host range of over 230 species and is a destructive pathogen of many crops and ornamental plants, including cotton (Gossypium barbadense L.), tobacco (Nicotiana tabacum L.) and mango (Mangifera indica L.) (Shukla et al. 2021; Toksoz and Rothrock 2009). This is the first report worldwide of B. basicola infecting lisianthus. This discovery is of great importance for Chinese flower growers because this fungus is well established in the observed area, and effective measures are needed to manage this disease.

Chromosome-scale genome assembly of Eustoma grandiflorum, the first complete genome sequence in family Gentianaceae

Eustoma grandiflorum (Raf.) Shinn., is an annual herbaceous plant native to the southern United States, Mexico, and the Greater Antilles. It has a large flower with a variety of colors and an important flower crop. In this study, we established a chromosome-scale de novo assembly of E. grandiflorum by integrating four genomic and genetic approaches: (1) Pacific Biosciences (PacBio) Sequel deep sequencing, (2) error correction of the assembly by Illumina short reads, (3) scaffolding by chromatin conformation capture sequencing (Hi-C), and (4) genetic linkage maps derived from an F2 mapping population. The 36 pseudomolecules and unplaced 64 scaffolds were created with total length of 1,324.8 Mb. Full-length transcript sequencing was obtained by PacBio Iso-Seq sequencing for gene prediction on the assembled genome, Egra_v1. A total of 36,619 genes were predicted on the genome as high confidence HC) genes. Of the 36,619, 25,936 were annotated functions by ZenAnnotation. Genetic diversity analysis was also performed for nine commercial E. grandiflorum varieties bred in Japan, and 254,205 variants were identified. This is the first report of the construction of reference genome sequences in E. grandiflorum as well as in the family Gentianaceae.

EN PRENSA Efecto de la estación de cultivo en el crecimiento y vida poscosecha de lisianthus (Eustoma grandiflorum L.) EN PRENSA

Plántulas de lisianthus ‘ABC 2-3 Blue’ fueron cultivadas bajo cubierta película plástica en Zacatepec, Morelos, en dos ciclos: otoño-invierno (noviembre - febrero) y primavera-verano (abril-junio) para cuantificar algunas variables morfológicas, azúcares solubles y fisiológicas durante su desarrollo y postcosecha que aporten información sobre el efecto de la época de cultivo en la calidad y vida útil. Los resultados indicaron que la altura fue similar en ambos ciclos de cultivo, sin embargo, el tiempo de cultivo fue mayor en otoño-invierno (117 días) que en primavera-verano (73 días). El área foliar, volumen de raíz y peso seco total y por estructuras fue significativamente mayor (P≤0.05) en otoño-invierno. El contenido de sacarosa fue mayor en las hojas en otoño-invierno y la glucosa en primavera-verano. En poscosecha las flores de lisianthus mostraron un incremento significativo en la velocidad de respiración y el peso fresco relativo en las flores del ciclo otoño-invierno, aunque existió menor número de flores abiertas (2) y una apariencia buena por un tiempo mayor (10 días) comparado con las flores de primavera-verano. El contenido de sacarosa en las hojas en poscosecha se incrementó sustancialmente, mientras que la glucosa y fructosa disminuyeron. En las flores la sacarosa se mantuvó en niveles altos por más tiempo en las flores cultivadas en otoño-invierno, mientras que las flores cultivadas en primavera-verano, la sacarosa, fructosa y glucosa disminuyeron drásticamente en poscosecha. La menor acumulación de materia seca y azúcares solubles en primavera-verano propicia una menor vida útil de lisianthus ‘ABC 2-3 Blue’.

Conservation and diversity in transcriptional responses among host plants forming distinct arbuscular mycorrhizal morphotypes

The morphotype of arbuscular mycorrhizal (AM) roots is distinct mostly depending on AM host species: Arum, Paris, and Intermediate types. We previously reported that gibberellin (GA) promotes the establishment of Paris-type AM symbiosis in Eustoma grandiflorum despite its negative effects on Arum-type AM symbiosis in model plants. However, the molecular mechanisms underlying the differential effects of GA on different morphotypes, including Intermediate-type AM symbiosis, remain elusive. Comparative transcriptomics revealed that several symbiosis-related genes were transcriptionally promoted upon AM fungal colonization in Lotus japonicus (Arum-type), Daucus carota (Intermediate-type), and E. grandiflorum (Paris-type). Interestingly, upon GA treatment, the fungal colonization levels and expression of symbiosis-related genes were suppressed in L. japonicus and D. carota but were promoted in E. grandiflorum. Exogenous GA transcriptionally inhibited the biosynthetic process of a host-derived signal molecule involved in AM symbiosis, strigolactone, in L. japonicus and E. grandiflorum. Additionally, disaccharides mainly metabolized in AM roots would be different between L. japonicus and D. carota/ E. grandiflorum. This study uncovered the conserved transcriptional responses during mycorrhization and diverse responses to GA in AM roots with distinct morphotypes among phylogenetically distant host plants.

Amonio y sulfato en el crecimiento, actividad fisiológica y estado nutrimental de las plantas de lisianthus cv. ABC 1-2 rosado oscuro

El nitrógeno (N) y azufre (S) son nutrimentos que tienen una fuerte interacción en sus vías de asimilación. Por lo tanto, la adición de estos en una adecuada proporción influye positivamente en el desarrollo de las plantas. El objetivo de este trabajo fue evaluar el efecto de la interacción de diferentes concentraciones de NH4+ y SO42- en variables de crecimiento, fisiológicas y de concentración de macronutrimentos en las plantas de lisianthus (Eustoma grandiflorum (Raf.) Shinn.) cv. ABC 1-2 Rosado Oscuro. Los tratamientos evaluados consistieron en tres concentraciones de NH4+ (0, 2.5 y 5 meq L-1) y dos concentraciones de SO42- (7 y 10 meq L-1). Las diferentes concentraciones de SO42- y NH4+ se diseñaron a partir de modificaciones de la solución nutritiva de Steiner. Se utilizaron contenedores de polietileno negro de 10 L y sustrato perlita con partículas de 0.2-0.5 mm de diámetro. Los resultados mostraron que el diámetro de tallo y la producción de biomasa seca en raíz, tallo, flor y total fueron mayores al suministrar 5 meq L-1 de NH4+ con 7 meq L-1 de SO42-. Por otro lado, el peso seco de hoja y altura de planta fue mayor al emplear 2.5 meq L-1 de NH4+ con 7 meq L-1 de SO42-. Este mismo comportamiento se observó en los parámetros de fotosíntesis, transpiración y conductancia estomática. La mayor concentración de N y P se obtuvo al emplear 2.5 meq L-1 de NH4+ con 10 meq L-1 de SO42-; asimismo, la concentración de Mg y S fue mayor con 2.5 meq L-1 de NH4+ en ambas concentraciones de SO42; mientras que K y Ca fue mayor al incrementar la concentración de NH4+ con 7 meq L-1 de SO42-. El mejor crecimiento, producción de biomasa y concentración de nutrimentos (K y Ca) de las plantas de lisianthus se obtiene con la proporción 5 meq L-1 de NH4+/ 7 meq L-1 de SO42-; mientras que, la actividad fisiológica es favorecida por la proporción 2.5 meq L-1 de NH4+ / 7 meq L-1 de SO42-.