The thylakoid membrane system of higher-plant chloroplasts consists of interconnected subdomains of appressed and non-appressed membrane bilayers, known as grana and stroma lamellae, respectively. The shaping of the cylindrical grana stacks is mediated, in a dosage-dependent manner, by CURT1 protein complexes, which facilitate membrane curvature at the grana margins, the interface between grana and stroma lamellae. Although grana stacks are highly conserved among land plants, the functional relevance of grana stacking remains unclear. Here we show that CURT1-related alteration of thylakoid ultrastructure reduces photosynthetic efficiency and plant fitness under adverse, controlled and natural light conditions. Plants that lack CURT1 are impaired in adjusting grana diameter, which compromises the effectiveness of regulatory mechanisms like PSII repair cycle and state transitions. Interestingly, CURT1A suffices to induce thylakoid membrane curvature in planta, and thylakoid hyper-bending that is observed in CURT1A overexpressor lines. We suggest that CURT1 oligomerisation is regulated at the post-translational level in a light-dependent fashion and CURT1-mediated thylakoid plasticity is critical for plant fitness and plays an important role in fine-tuning photosynthesis under challenging growth conditions.

Abscisic acid (ABA) plays important roles in positively or negatively regulating plant disease resistance to pathogens. Here, we reassess the role of endogenous and exogenous ABA by using: 35S::ABA2, a previously reported transgenic Arabidopsis line with increased endogenous ABA levels; aba2-1, a previously reported ABA2 mutant with reduced endogenous ABA levels; and exogenous application of ABA. We found that bacterial susceptibility promoted by exogenous ABA was suppressed in 35S::ABA2 plants. The 35S::ABA2 and aba2-1 plants displayed elevated and reduced levels, respectively, of bacterial flagellin peptide (flg22)-induced H₂O₂. Surprisingly, ABA pre-treatment reduced flg22-induced H₂O₂ generation. Exogenous, but not endogenous ABA, increased catalase activity. Loss of nicotinamide adenine dinucleotide phosphate oxidase genes, RBOHD and RBOHF, restored exogenous ABA-promoted bacterial susceptibility of 35S::ABA2 transgenic plants. In addition, endogenous and exogenous ABA had similar effects on callose deposition and salicylic acid (SA) signaling. These results reveal an underlying difference between endogenous and exogenous ABA in regulating plant defense responses. Given that some plant pathogens are able to synthesize ABA and affect endogenous ABA levels in plants, our results highlight the importance of reactive oxygen species in the dual function of ABA during plant-pathogen interactions.

Viral infection can regulate the cell cycle, thereby promoting viral replication. Hijacking and altering the cell cycle are important for the virus to establish and maintain a latent infection. Previously, Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV)-latently infected P8-Se301-C1 cells, which grew more slowly than Se301 cells and interfered with homologous SeMNNPV superinfection, were established. However, the effects of latent and superinfection with baculoviruses on cell cycle progression remain unknown. In this study, the cell cycle profiles of P8-Se301-C1 cells and SeMNPV or Autographa californica multiple nucleopolyhedrovirus (AcMNPV)-infected P8-Se301-C1 cells were characterized by flow cytometry. The results showed that replication-related genes MCM4, PCNA, and BAF were down-regulated (p < 0.05) in P8-Se301-C1 cells, and the S phase of P8-Se301-C1 cells was longer than that of Se301 cells. P8-Se301-C1 cells infected with SeMNPV did not arrest in the G2/M phase or affect the expression of Cyclin B and cyclin-dependent kinase 1 (CDK1). Furthermore, when P8-Se301-C1 cells were infected with SeMNPV after synchronized treatment with hydroxyurea and nocodazole, light microscopy and qRT-PCR analysis showed that, compared with unsynchronized cells and S and G2/M phase cells, SeMNPV-infected P8-Se301-C1 cells in G1 phase induced G2/M phase arrest, and the amount of virus adsorption and intracellular viral DNA replication were significantly increased (p < 0.05). In addition, budded virus (BV) production and occlusion body (OB)-containing cells were both increased at 120 h post-infection (p < 0.05). The expression of Cyclin B and CDK1 was significantly down-regulated at 48 h post-infection (p < 0.05). Finally, the arrest of SeMNPV-infected G1 phase cells in the G2/M phase increased BV production (p < 0.05) and the number of OB-containing cells. In conclusion, G1 phase infection and G2/M arrest are favorable to SeMNPV proliferation in P8-Se301-C1 cells, thereby alleviating the homologous superinfection exclusion. The results contribute to a better understanding of the relationship between baculoviruses and insect cell cycle progression and regulation.

Dumasia (Fabaceae, tribe Phaseoleae, subtribe Glycininae), a genus of trifoliate vines, is widely distributed in tropical and subtropical regions of Asia and Africa (Pan & Zhu 2010). In October 202...

Aucuba japonica is a plant with colorful leaves that is widely used in landscaping. Due to its shade tolerance and cold resistance (Li et al. 2013), A. japonica has become a dominant plant species in Guiyang city, China. From 2018 to 2021, an anthracnose disease was observed on A. japonica in Huaxi District (26°23'03'' N, 106°37'58'' E), Guiyang, Guizhou Province. The incidence of anthracnose in newly planted A. japonica reached 90%, resulting in a mortality rate of 30%. This has become a major disease for A. japonica in Guiyang. Typical symptoms include faded spots that initially appear at the infection center, followed by black-brown lesions with irregular edges. At the latter stage, slightly raised black spots are seen arranged in a wheel pattern. In severe cases, diseased leaves fall off. To identify the pathogen, leaf pieces (5 mm × 3 mm) containing symptomatic tissue with healthy margins were excised. The pieces were sterilized with 75% ethanol for 1 min, rinsed three times with sterile water, and cultured on potato dextrose agar (PDA) in Petri dishes at 26°C. White to cream colonies were developed after growth on PDA for 2 days. Mycelial growth ranged from 4.8 to 5.0 mm/day. Conidia were cylindrical, obtuse apex, and protruding base, with dimensions of 18.5 to 20.0 × 7.0 to 9.0 μm (n = 20). Conidial length:breadth ratio was 2-3 (n = 20). Acervuli and sclerotia had not been seen on PDA. To confirm the species of the isolate, PCR was performed on extracted DNA to amplify the ribosomal DNA internal transcribed spacer (ITS), a 200-bp intron of the glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a partial sequence of the calmodulin (CAL) gene, and the large subunit (LSU) region by using the primer pairs ITS1/ITS4 (Schoch et al. 2012), GDF1/GDR1 (Guerber et al. 2003), CAL228F/CAL737R (Carbone & Kohn 1999), and NL1/NL4 (Ziemiecki et al. 1990), respectively. The obtained 553 bp ITS sequence (Genbank accession no. MZ424503) showed 99.82% similarity with several C. boninense sequences (MN429163, MN542218, KM520024, and KM520014). The obtained 233 bp GAPDH sequence (OM643394) showed 99.07% similarity with C. boninense (MT602277, GQ221769, MK544890, and MK544888). The obtained 763 bp CAL sequence (OM313386) showed 99.32% similarity with C. boninense (MK569127). The obtained 584 bp LSU sequence (OK513272) showed 99.83% similarity with C. boninense (MH876452, MH877053, and MH876450). Phylogenic trees based on the sequences of ITS, GAPDH, and CAL (Damm et al. 2012), the species of isolate was confirmed as C. boninense. To confirm pathogenicity and to fulfill Koch's postulates, leaves of five A. japonica plants were wounded with a sterilized hypodermic needle and inoculated with 1 μL of a conidial suspension (106 conidia/mL). As control, 5 plants were inoculated with 1 μL of sterile water. After 7 days in a moist climate chamber at 26°C under a 16 h/8 h light/dark cycle, symptoms appeared on all inoculated leaves, while the control leaves remained healthy. The pathogen was reisolated from the inoculated leaves, and was confirmed to be C. boninense using the same morphological and molecular methods as before. C. boninense has been reported to infect many plant species, including Capsicum annuum, Rosa chinensis, and Eucalyptus robusta (Ding et al. 2021; Tozze et al. 2009; Zhang et al. 2018). Another Colletotrichum pathogen, C. fructicola, was reported to cause anthracnose on A. japonica in China (Gong et al. 2016). To our knowledge, this is the first report of A. japonica anthracnose disease caused by C. boninense in Guizhou province, China. Identifying this pathogen provides a foundation to prevent this complex disease and to reduce economic loss.