SUMMARYThe interaction between legumes and arbuscular mycorrhizal (AM) fungi is vital to the development of sustainable plant production systems. Here, we focus on a putative MYB-like (LjMAMI) transcription factor (TF) previously reported to be highly upregulated in Lotus japonicus mycorrhizal roots. Phylogenetic analyses revealed that the protein is related to a group of TFs involved in phosphate (Pi) starvation responses, the expression of which is independent of the Pi level, such as PHR1. GUS transformed plants and quantitative reverse transcription PCR revealed strong gene induction in arbusculated cells, as well as the presence of LjMAMI transcripts in lateral root primordia and root meristems, even in the absence of the fungus, and independently of Pi concentration. In agreement with its putative identification as a TF, an eGFP-LjMAMI chimera was localized to the nuclei of plant protoplasts, whereas in transgenic Lotus roots expressing the eGFP-LjMAMI fusion protein under the control of the native promoter, the protein was located in the nuclei of the arbusculated cells. Further expression analyses revealed a correlation between LjMAMI and LjPT4, a marker gene for mycorrhizal function. To elucidate the role of the LjMAMI gene in the mycorrhizal process, RNAi and overexpressing root lines were generated. All the lines retained their symbiotic capacity; however, RNAi root lines and composite plants showed an important reduction in root elongation and branching in the absence of the symbiont. The results support the involvement of the AM-responsive LjMAMI in non-symbiotic functions: i.e. root growth.

Background The rice weevil Sitophilus oryzae is one of the most important agricultural pests, causing extensive damage to cereal in fields and to stored grains. S. oryzae has an intracellular symbiotic relationship (endosymbiosis) with the Gram-negative bacterium Sodalis pierantonius and is a valuable model to decipher host-symbiont molecular interactions. Results We sequenced the Sitophilus oryzae genome using a combination of short and long reads to produce the best assembly for a Curculionidae species to date. We show that S. oryzae has undergone successive bursts of transposable element (TE) amplification, representing 72% of the genome. In addition, we show that many TE families are transcriptionally active, and changes in their expression are associated with insect endosymbiotic state. S. oryzae has undergone a high gene expansion rate, when compared to other beetles. Reconstruction of host-symbiont metabolic networks revealed that, despite its recent association with cereal weevils (30 kyear), S. pierantonius relies on the host for several amino acids and nucleotides to survive and to produce vitamins and essential amino acids required for insect development and cuticle biosynthesis. Conclusions Here we present the genome of an agricultural pest beetle, which may act as a foundation for pest control. In addition, S. oryzae may be a useful model for endosymbiosis, and studying TE evolution and regulation, along with the impact of TEs on eukaryotic genomes.

One sentence summary: Expression of PDX1.2 is regulated by the HSFA1 transcription factor 15family and is an important abiotic stress tolerance strategy in most eudicots that is not utilized by 16 monocots such as grasses. ABSTRACT 28Plants sense temperature changes and respond by altering growth and metabolic activity to 29 acclimate to the altered environmental conditions. The B vitamins give rise to vital coenzymes that 30 are indispensable for growth and development but their inherent reactive nature renders them prone 31 to destruction especially under stress conditions. Therefore, plant survival strategies would be 32 expected to include mechanisms to sustain B vitamin supply under demanding circumstances. Here, 33 using the example of vitamin B 6 , we investigate the regulation of biosynthesis across eudicot and 34 monocot species under heat stress. Most eudicots carry a pseudoenzyme PDX1.2 that is a non-35 catalytic homolog of the PDX1 subunit of the vitamin B 6 biosynthesis protein machinery, 36 PYRIDOXINE SYNTHASE. Using Arabidopsis and tomato as models, we show that PDX1.2 is 37 transcriptionally regulated by the HSFA1 transcription factor family. Monocots only carry catalytic 38 PDX1 homologs but do not respond to heat stress as demonstrated for rice and maize, suggesting 39 fundamental differences in the regulation of vitamin B 6 biosynthesis across the two lineages. 40Investigation of the molecular mechanism of PDX1.2 transcription reveals two alternative 41 transcriptional start sites one of which is exclusive to heat stress. Further data suggest that PDX1.2 42 leads to stabilization of the catalytic PDX1s under heat stress conditions, which would serve to 43 maintain vitamin B 6 homeostasis in times of need in eudicots that carry this gene. Our analyses 44indicate an important abiotic stress tolerance strategy in several eudicots, which has not been 45 evolutionarily adapted (or is not required) by monocots such as grasses. INTRODUCTION 47The B vitamins are essential for survival of all organisms, as they provide important coenzymes for 48 numerous cellular proteins and have more recently been implicated in non-coenzyme related 49 activities (Colinas & Fitzpatrick, 2015). Plants are autonomous for these compounds 50 biosynthesizing them de novo from relatively simple precursors and are a major source of 51 micronutrients required by animals, including humans (Fitzpatrick et al., 2012). Being chemically 52 reactive by nature as coenzymes and vital for cellular function, it is important that homeostasis of B 53 vitamins is maintained with supply and demand of these compounds needing to be strictly 54 coordinated. In this context, the devastating developmental and physiological effects that 55 deficiencies in the B vitamin compounds can have on an organism, in particular humans, is 56 thoroughly documented, as well as consequences of oversupply (Kennedy, 2016, Spector & 57 Johanson, 2007. In plants, while there are numerous reports on B vitamin metabolism per se 58 (biosynthesis, transport), th...

Beetles thriving on tyrosine-poor diet sources often develop mutualistic associations with endosymbionts able to synthesize aromatic amino acids. This surplus of aromatic amino acids is used to reinforce the insect’s protective cuticle.

Insects living in nutritionally poor environments often establish long-term relationships with intracellular bacteria that supplement their diets and improve their adaptive and invasive powers. Even though these symbiotic associations have been extensively studied on physiological, ecological and evolutionary levels, few studies have focused on the molecular dialogue between host and endosymbionts to identify genes and pathways involved in endosymbiosis control and dynamics. We simultaneously analyzed host and endosymbiont gene expression during the life cycle of the cereal weevilSitophilus oryzae, from larval stages to adults, with a particular emphasis on emerging adults where the endosymbiontSodalis pierantoniusexperiences a contrasted growth-climax-elimination dynamics. We unraveled a constant arms race in which different biological functions are intertwined and coregulated across both partners. These include immunity, metabolism, metal control, apoptosis, and bacterial stress response. Particularly, genes from the Hippo regulatory pathway are specifically induced by endosymbiont growth, while the regulation of metal ions constitutes the basis of the arms race between the two partners at the onset of the bacterial load climax. The study of these tightly regulated functions, which are at the center of symbiotic regulations, provides evidence on how hosts and bacteria finely tune their gene expression and respond to different physiological challenges constrained by insect development in a nutritionally limited ecological niche.

The dominant gene Rdg2a of barley conferring resistance to the hemi-biotrophic seed-borne pathogen Pyrenophora graminea is located in the distal region of chromosome arm 1 (7H)S. As the first step towards isolating the gene, a high-resolution genetic map of the region was constructed using an F(2) population of 1,400 plants (Thibaut Rdg2axMirco). The map included six classes of resistance gene analogues (RGAs) tightly associated with Rdg2a. Rdg2a was delimited to a genetic interval of 0.14 cM between the RGAs ssCH4 and MWG851. Additional markers were generated using the sequence from the corresponding region on rice chromosome 6, allowing delimitation of the Rdg2a syntenic interval in rice to a 115 kbp stretch of sequence. Analysis of the rice sequence failed to reveal any genes with similarity to characterized resistance genes. Therefore, either the rice-barley synteny is disrupted in this region, or Rdg2a encodes a novel type of resistance protein.

Many insects house symbiotic intracellular bacteria (endosymbionts) that provide them with essential nutrients, thus promoting usage of nutrient-poor habitats. Endosymbiont seclusion within host specialized cells, called bacteriocytes, often organized in a dedicated organ, the bacteriome, is crucial in protecting them from host immune defenses while avoiding chronic host immune activation. Previous evidence obtained in the cereal weevil Sitophilus oryzae has shown that bacteriome immunity is activated against invading pathogens, suggesting endosymbionts might be targeted and impacted by immune effectors during an immune challenge. To pinpoint any molecular determinants associated with such challenges, we conducted a dual transcriptomic analysis of S. oryzae's bacteriome subjected to immunogenic peptidoglycan fragments. We show that upon immune challenge the bacteriome actively participates in the innate immune response via a burst of antimicrobial peptides (AMPs). Surprisingly, endosymbionts do not undergo any transcriptomic changes, indicating that this potential threat goes unnoticed. Immunohistochemistry of selected AMPs show that these are secreted outside the bacteriome, excluding direct contact with the endosymbionts. This work demonstrates that endosymbiont protection during an immune challenge is mainly achieved by efficient confinement within bacteriomes, which provides physical separation between host systemic response and endosymbionts.

Insects often establish long-term relationships with intracellular symbiotic bacteria, i.e. endosymbionts, that provide them with essential nutrients such as amino acids and vitamins. Endosymbionts are typically confined within specialized host cells called bacteriocytes that may form an organ, the bacteriome. Compartmentalization within host cells is paramount for protecting the endosymbionts and also avoiding chronic activation of the host immune system. In the cereal weevil Sitophilus oryzae, bacteriomes are present as a single organ at the larval foregut-midgut junction, and in adults, at the apex of midgut mesenteric caeca and at the apex of the four ovarioles. While the adult midgut endosymbionts experience a drastic proliferation during early adulthood followed by complete elimination through apoptosis and autophagy, ovarian endosymbionts are maintained throughout the weevil lifetime by unknown mechanisms. Bacteria present in ovarian bacteriomes are thought to be involved in the maternal transmission of endosymbionts through infection of the female germline, but the exact mode of transmission is not fully understood. Here, we show that endosymbionts are able to colonize the germarium in one-week-old females, pinpointing a potential infection route of oocytes. To identify potential immune regulators of ovarian endosymbionts, we have analyzed the transcriptomes of the ovarian bacteriomes through young adult development, from one-day-old adults to sexually mature ones. In contrast with midgut bacteriomes, immune effectors are downregulated in ovarian bacteriomes at the onset of sexual maturation. We hypothesize that relaxation of endosymbiont control by antimicrobial peptides might allow bacterial migration and potential oocyte infection, ensuring endosymbiont transmission.