Background Chloroplast development is coordinately regulated by plastid- and nuclear-encoding genes. Although many regulators have been reported to be involved in chloroplast development, new factors remain to be identified, given the complexity of this process. Results In this study, we characterized a rice mutant lethal albinic seedling 1 ( las1 )form of a 4-hydroxy-3-methylbut-2-enyl diphosphate reductase (OsHMBPP) that was targeted to the chloroplasts. The LAS1 mutation caused the albino lethal phenotype in seedlings. Transmission electron microscopy indicated that las1 were defective in early chloroplast development. LAS1 is preferentially expressed in leaves, implying its role in controlling chloroplast development. The expression levels of many chloroplast-encoded genes were altered significantly in las1 . The expression levels of nuclear-encoded gene involved in Chl biosynthesis were also decreased in las1 . We further investigated plastidic RNA editing in las1 and found that the edit efficiency of four chloroplast genes were markly altered. Compared with WT, las1 exhibited defective in biogenesis of chloroplast ribosomes. Conclusions Our results show that LAS1/OsHMBPP plays an essential role in the early chloroplast development in rice.

There are more than 2035 Begonia species (Begoniaceae) reported currently in the world. Begonia arachnoidea was found as a new species within a small area in Southern China. In this study, we are reporting for the first time its chloroplast genome for the purpose to compare with the chloroplast genomic data from other plant taxa which were closely related to this new species. Our results show that the circular chloroplast genome of B. arachnoidea is 169,725 bp in length, with 35.49% GC content. The whole structure of the genome has 76,431 bp in a large single-copy (LSC) region, 18,146 bp in a small single-copy (SSC) region, and the two inverted repeat (IRs) regions are both 37,574 bp. There are 90 protein-coding genes, 8 rRNA genes, and 42 tRNA genes encoded in this genome. Final phylogenetic analysis revealed that B. arachnoidea is genetically closest to B. pulchrifolia and B. coptidifolia .

Hybrid mandevilla (Mandevilla × amabilis) is an ornamental plant widely grown in southern China, appreciated for its large bright-color flowers and heat tolerance (Oder et al. 2016). In June to August 2019, an anthracnose disease was observed on hybrid mandevilla plants in a nursery in Nanning, Guangxi, China (108˚14’30’’E, 22˚51’02’’N). Symptoms began as red-brown spots, which gradually enlarged (0.2 to 1.1 cm in width and 0.3 to 1.5 cm in length), overlapped, and extended until the leaves wilted. Of the 70 plants surveyed, more than 80% of leaves showed these symptoms. To determine the causal agent, samples were gathered from symptomatic leaves, cut into 3 × 3 mm pieces, surface-sterilized with 75% ethanol for 10 s and 2% NaClO for two min, and rinsed three times in sterile water. The pieces were placed onto potato dextrose agar (PDA) and incubated at 25°C in the darkness. After six days, hyphal margins were transferred onto fresh PDA and incubated at 25°C. Cultures grown on PDA started as grey-white, turned dark grey after nine days of growth, and conidia were produced after 13 days. Conidia were hyaline, guttulate, unicellular, cylindrical, and averaged 15.74 × 5.84 μm. Three single-spore isolates, PXT1-1, PXT1-5, and PXT2-1, were selected for molecular identification. The rDNA internal transcribed spacer region (ITS), a partial sequence of the actin gene (ACT), the chitin synthase 1 gene (CHS), glyceraldehyde-3-phosphate dehydrogenase gene (GAPDH), beta-tubulin (TUB2), and the intergenic region of apn2 and MAT1-2-1 genes (ApMat) of isolates PXT1-1, PXT1-5, and PXT2-1 were amplified with the primer pairs ITS1/ITS4, ACT-512F/ACT-783R, CHS-79F/CHS-354R, GDF1/GDR1, T1/Bt-2b (Weir et al. 2012), and AM-F/AM-R (Silva et al. 2012), respectively. The sequences were compared with the GenBank nucleotide sequence database and had more than 99% similarity to ITS (JX010165), ACT (FJ907426), CHS (JX009866), GAPDH (JX010033), TUB2 (JX010405), and ApMat (JQ807838) of isolate ICMP18581 of Colletotrichum fructicola Prihastuti, L. Cai & K. D. Hyde. The sequences were deposited into GenBank (Accessions MT193419 to MT193421 for ITS, MT193101 to MT193103 for ACT, MT193098 to MT193100 for CHS, MT193095 to MT193097 for GAPDH, MT193092 to MT193094 for TUB2, and MT193089 to MT193091 for ApMat of the three isolates, respectively). Based on the genetic and morphological results, the isolates were identified as C. fructicola. Pathogenicity was tested on 72 healthy leaves from nine 2-year-old hybrid mandevilla plants (eight leaves per plant) in November 2019 in a greenhouse using isolates PXT1-1, PXT1-5, and PXT2-1. Two wounds were made slightly on both sides of the middle vein on each leave using a sterilized toothpick, and each wounded site was inoculated with 10 μl of a 1 × 106 conidia/ml suspension. Leaves of three plants were treated with sterile water for the control. Plants were covered with plastic bags to maintain high humidity and placed in a greenhouse kept at 28°C with a 12-h photoperiod. At five days post-inoculation, all the inoculated leaves developed dark brown lesions (0.1 to 1.4 cm in width and 0.2 to 1.6 cm in length), while controls remained disease free. The fungus was re-isolated from symptomatic inoculated leaves and identification confirmed by morphology and sequencing, fulfilling Koch’s postulates. Colletotrichum fructicola can cause leaf diseases in a variety of crops and ornamental plants, including apple, tea plants, sage, and orchid (Guarnaccia et al. 2019; Kim et al. 2018). To our knowledge, this is the first report of C. fructicola causing anthracnose on hybrid mandevilla in China. These findings provide a foundation for future studies on the epidemiology and control of anthracnose caused by C. fructicola on hybrid mandevilla.

Begonia L. (Begoniaceae) is the sixth largest genus in the world which consists of more than 2,039 species. Many species of Begonia have highly ornamental leaves and flowers, so they are mainly used for ornamental purposes, and some species can also be used as medicines or vegetables. Begonia gulongshanensis is a newly discovered species in 2018 which occurs exclusively in Jingxi county in Southern China, however, there are few studies on the molecular biology and phylogeny of this species currently. Therefore, we report its complete chloroplast genome sequence for the first time, hoping to provide a foundation for its future phylogenetic analysis. The chloroplast genome of B. gulongshanensis was 169,153 bp in size, which contained a large single-copy region of 75,998 bp, a small single-copy region of 18,063 bp, and two inverted repeat regions of the same 37,546 bp. The total GC content was 35.51%. The genome encodes 42 transfer RNA genes, 8 ribosomal RNA genes and 90 protein-coding genes. The phylogenetic analysis indicated that the genetic relationship between B. gulongshanensis and the other three begonias was very close, but there was still certain distance.

Both Impatiens macrovexilla and I . macrovexilla var. yaoshanensis have potential to be exploited as ornamental plants, despite some of their morphological differences. In the present study, the complete chloroplast genome sequences of the two taxa are reported for the first time, which could facilitate their infraspecies classification, and analyses of their evolution, phylogeny, and breeding potential. The chloroplast genomes of I . macrovexilla and I . macrovexilla var. yaoshanensis were 152,437 and 152,286 bp in size, respectively. Their total GC contents were 36.77 and 36.80%, respectively. Both genomes contained 88 protein-coding genes, 8 rRNA genes, and 37 tRNA genes. The phylogenetic analysis revealed that the two specimens clustered next to each other and were closely related to I . alpicola , I . fanjingshanica , and I . piufanensis , but relatively distant from I . guizhouensis and I . pritzelii .