Moso bamboo (Phyllostachys edulis) is one of the most important bamboo species in China and the third most important plant species for timber production. However, the dwarf variant of moso bamboo, P. edulis f. tubaeformis (shengyin bamboo), which has shortened internodes, is not well studied. We used anatomical, hormonal, and transcriptomic approaches to study internode shortening and shoot growth in dwarf shengyin and wild moso bamboo. Phenotypic and anatomical observations showed that dwarfing in shengyin bamboo is due to reduced internode length, and the culm fibers in shengyin bamboo are significantly shorter and thicker than in wild moso bamboo. We measured the levels of endogenous hormones in the internodes and found that shengyin bamboo had lower levels of four hormones while two others were higher in wild moso bamboo. Comparative transcriptome analyses revealed a potential regulating mechanism for internode length involving genes for cell wall loosening-related enzymes and the cellulose and lignin biosynthesis pathways. Genes involved in hormone biosynthesis and signal transduction, especially those that showed significant differential expression in the internodes between shengyin and wild moso bamboo, may be important in determining the shortened internode phenotype. A hypothesis involving possible cross-talk between phytohormone signaling cues and cell wall expansion leading to dwarfism in shengyin bamboo is proposed. The results presented here provide a comprehensive exploration of the biological mechanisms that determine internode shortening in moso bamboo.

Communication between insects and plants relies on the exchange of bioactive molecules that traverse the species interface. Although proteinic effectors have been extensively studied, our knowledge of other molecules involved in this process remains limited. In this study, we investigate the role of salivary microRNAs (miRNAs) from the rice planthopper Nilaparvata lugens in suppressing plant immunity. A total of three miRNAs were confirmed to be secreted into host plants during insect feeding. Notably, the sequence-conserved miR-7-5P is specifically expressed in the salivary glands of N. lugens and is secreted into saliva, distinguishing it significantly from homologues found in other insects. Silencing miR-7-5P negatively affects N. lugens feeding on rice plants, but not on artificial diets. The impaired feeding performance of miR-7-5P-silenced insects can be rescued by transgenic plants overexpressing miR-7-5P. Through target prediction and experimental testing, we demonstrate that miR-7-5P targets multiple plant genes, including the immune-associated bZIP transcription factor 43 (OsbZIP43). Infestation of rice plants by miR-7-5P-silenced insects leads to the increased expression of OsbZIP43 , while the presence of miR-7-5P counteracts this upregulation effect. Furthermore, overexpressing OsbZIP43 confers plant resistance against insects which can be subverted by miR-7-5P. Our findings suggest a mechanism by which herbivorous insects have evolved salivary miRNAs to suppress plant immunity, expanding our understanding of cross-kingdom RNA interference between interacting organisms.

Dendrobium is one of the largest genera in the Orchidaceae, and D. officinale is used in traditional medicine, particularly in China. D. officinale seeds are minute and contain limited energy reserves, and colonization by a compatible fungus is essential for germination under natural conditions. When the orchid mycorrhizal fungi (OMF) initiates symbiotic interactions with germination-driven orchid seeds, phytohormones from the orchid or the fungus play key roles, but the details of the possible biochemical pathways are still poorly understood. In the present study, we established a symbiotic system between D. officinale and Tulasnella sp. for seed germination. RNA-Seq was used to construct libraries of symbiotic-germinated seeds (DoTc), asymbiotic-germinated seeds (Do), and free-living OMF (Tc) to investigate the expression profiles of biosynthesis and metabolism pathway genes for three classes of endogenous hormones: JA (jasmonic acid), ABA (abscisic acid) and SLs (strigolactones), in D. officinale seeds and OMF under symbiotic and asymbiotic conditions. Low concentrations of endogenous JA, ABA, or SLs were detected in the D. officinale-Tulasnella symbiont compared with the asymbiotic tissues. Gene annotation results suggest that the expression of DEGs (differentially expressed genes) related to JA and ABA biosynthesis from D. officinale were down-regulated, while most of the key DEGs related to SL biosynthesis from D. officinale were up-regulated in the symbiotic germinated seeds compared with the asymbiotic germinated seeds. Moreover, in the OMF, we found a significantly up-regulated differential expression of the JA and ABA biosynthesis-related genes in the symbiotic interaction, with the opposite expression trends to those found in Dendrobium. This indicates that Dendrobium seed symbiotic germination may be stimulated by the apparent involvement of the OMF in the production of hormones, and relatively low concentrations of endogenous JA, ABA, or SLs might be maintained to promote the growth of the D. officinale-Tulasnella symbiotic protocorm-like body. These results will increase our understanding of the possible roles played by endogenous hormones in the regulation of the orchid-fungus symbiosis.

Paphiopedilum armeniacum S. C. Chen et F. Y. Liu is an endangered lady’s slipper orchid species with high horticultural value. As observed for other orchids, mycorrhizal fungi and endophytic bacteria play important roles in the growth and development of P. armeniacum. In the present study, the community structure dynamics across three growth and development stages of cultivated P. armeniacum were investigated. The potential interactions between Tulasnellaceae fungi and core bacterial genera on one hand and the stability of the presumed mycorrhizal fungi communities on the other were analyzed in three growth stages of P. armeniacum to enhance our understanding of endophytic microbial community structure dynamics in the roots at different development stages. Based on sequencing, 3 and 16 phyla and 59 and 269 genera were identified in the fungal and bacterial communities, respectively. The predominant fungi and bacteria were Basidiomycota (62.90%) and Proteobacteria (43.98%), which exhibited changes in abundance and diversity depending on the growth stage of P. armeniacum. Assessment of the entire microbial communities from different growth stages showed that the seedling stage had the highest richness and diversity. The microbial communities recruited by P. armeniacum at the seedling stage were different from those recruited at the vegetative and reproductive growth stages, and the microbial communities recruited in the latter two stages overlapped. Tulasnellaceae were the only dominant fungal symbionts during P. armeniacum growth. Brevibacillus, Mycobacterium, and Sphingomonas, the three core genera, showed significant interactions with the main OTUs of Tulasnellaceae. Putative mycorrhizal fungi in P. armeniacum were relatively stable across different growth environments, and the core mycorrhizal fungi were uncultured Tulasnellaceae (OTU1). This could facilitate the ex situ conservation and commercial development of the endangered orchid.