Microtubule-based perception of mechanical conflicts controls plant organ morphogenesis

ABSTRACTPrecise coordination between cells and tissues is essential for differential growth in plants. During lateral root formation in Arabidopsis thaliana, the endodermis is actively remodeled to allow outgrowth of the new organ. Here, we show that microtubule arrays facing lateral root founder cells display a higher order compared to arrays on the opposite wall of the same cell, and this asymmetry is required for endodermal remodeling and lateral root initiation. We identify that MICROTUBULE ASSOCIATED PROTEIN 70-5 is necessary for the establishment of this spatially defined microtubule organization and endodermis remodeling, and thus contributes to lateral root morphogenesis. We propose that MAP70-5 and cortical microtubule arrays in the endodermis integrate the mechanical signals generated by lateral root outgrowth, facilitating the channeling of organogenesis.

Genome-Wide Identification and Expression Analysis of AP2/EREBP Transcription Factors in Litchi (Litchi chinensis Sonn.)

APETALA2/ethylene response element binding proteins (AP2/EREBP) are a vital type of TF involved in plant organ development and embryogenesis. In this study we identified 202 Litchi AP2/EREBP TFs from the litchi genome. They were classified into four subfamilies by phylogenetic clustering, including AP2s (20), ERFs (112), DREBs (64), and RAVs (6). Analysis of conserved domains, motifs, gene structure, and genome localization were carried out to investigate the evolutionary features of litchi AP2/EREBPs. Over 35% of DREBs and ERFs involved in the expansion of litchi AP2/EREBPs resulted from tandem duplication. The majority of genomic organizations were conservative, except those of the AP2 subfamily, which had no intron and contained less conservative motif numbers. The expression profiles of litchi AP2/EREBPs in ten tissues were investigated using RNA-Seq data and fifty-nine showed tissue-specific expressions. Their expression patterns were confirmed by qRT-PCR with eight tissues-specificity genes. Six genes related to embryogenesis were identified using the map of orthologous gene interaction between Arabidopsis and litchi. This paper is a comprehensive report on the characteristics of the litchi AP2/EREBP gene superfamily. It will serve to further explore the regulatory mechanisms of AP2/EREBP TFs in the litchi somatic embryogenesis and provide information for litchi molecular breeding.

A digital sensor to measure real-time leaf movements and detect abiotic stress in plants

Plant and plant organ movements are the result of a complex integration of endogenous growth and developmental responses, partially controlled by the circadian clock, and external environmental cues. Monitoring of plant motion is typically done by image-based phenotyping techniques with the aid of computer vision algorithms. Here we present a method to measure leaf movements using a digital inertial measurement unit (IMU) sensor. The lightweight sensor is easily attachable to a leaf or plant organ and records angular traits in real-time for two dimensions (pitch and roll) with high resolution (measured sensor oscillations of 0.36° ± 0.53° for pitch and 0.50° ± 0.65° for roll). We were able to record simple movements such as petiole bending, as well as complex lamina motions, in several crops, ranging from tomato to banana. We also assessed growth responses in terms of lettuce rosette expansion and maize seedling stem movements. The IMU sensors are capable of detecting small changes of nutations (i.e., bending movements) in leaves of different ages and in different plant species. In addition, the sensor system can also monitor stress-induced leaf movements. We observed that unfavorable environmental conditions evoke certain leaf movements, such as drastic epinastic responses, as well as subtle fading of the amplitude of nutations. In summary, the presented digital sensor system enables continuous detection of a variety of leaf motions with high precision, and is a low-cost tool in the field of plant phenotyping, with potential applications in early stress detection.

A Large Root Phenome Dataset Wide-Opened the Potential for Underground Breeding in Soybean

The root is the most critical plant organ for water and nutrient acquisition. Although the root is vital for water and nutrient uptake, the diverse root characters of soybean still need to be identified owing to the difficulty of root sampling. In this study, we used 150 wild and 50 cultivated soybean varieties to collect root image samples. We analyzed root morphological traits using acquired-image. Except for the main total length (MTL), the root morphological traits for most cultivated and wild plants were significantly different. According to correlation analysis, the wild and cultivated plants showed a significant correlation among total root length (TRL), projected area (PA), forks, total lateral length (TLL), link average diameter, and MTL. In particular, TRL was highly correlated with PA in both cultivated (0.92) and wild (0.82) plants compared with between MTL (0.43 for cultivated and 0.27 for wild) and TLL (0.82 for cultivated and 0.52 for wild). According to principal component analysis results, both plants could be separated; however, there was some overlap of the traits among the wild and cultivated individuals from some regions. Nevertheless, variation among the cultivated plants was higher than that found in the wild plants. Furthermore, three groups, including MTL, TLL, and the remaining traits, could explain all the variances.

Accurate Direct PCR with Arabidopsis and rice

Methods for PCR that avoid costly and time consuming plant DNA purification have not been widely adopted, partly because their efficacy is unclear. Here, we compare different sampling methods for Direct PCR in Arabidopsis and rice. CutTip, stabbing a pipette tip into a plant organ and depositing the tip of the pipette tip into the reaction buffer, yielded high accuracy for genotyping and detection of CRISPR-induced mutations. This did not require visible tissue fragments in the reactions. We demonstrate the usefulness of this method in sampling many locations within a single plant to identify a rare CRISPR-mutated sector. These methods are simple, inexpensive and can help address the challenge of genotyping and genome editing at different scales with high accuracy. The methods also simplify the application of PCR in the field.

Culture Media Based on Leaf Strips/Root Segments Create Compatible Host/Organ Setup for in vitro Cultivation of Plant Microbiota

Plant microbiota have co-evolved with their associated plants in the entire holobiont, and their assemblages support diversity and productivity on our planet. Of importance is in vitro cultivation and identification of their hub taxa for possible core microbiome modification. Recently, we introduced the in situ-similis culturing strategy, based on the use of plant leaves as a platform for in vitro growth of plant microbiota. Here, the strategy is further extended by exploring plant organ compatible cultivation of plant microbiota when grown on corresponding leaf/root-based culture media. Pooling the advantages of MPN enrichment methodology together with natural plant-only-based culture media, the introduced method efficiently constructed a nutritional milieu governed by vegan nutrients of plant origin, i.e., leaf strips/root segments, immersed in plain semi-solid water agar. MPN estimates exceeded log 7.0 and 4.0 g−1 of endo-rhizosphere and endo-phyllosphere, respectively, of maize and sunflower; being proportionate to those obtained for standard culture media. With sunflower, PCR-DGGE analyses indicated divergence in community composition of cultivable endophytes primarily attributed to culture media, signaling a certain degree of plant organ affinity/compatibility. Based on 16S rRNA gene sequencing of bacterial isolates, 20 genera comprising 32 potential species were enriched; belonged to Bacteroidetes, Firmicutes, and Alpha-/Gammaproteobacteria. The described cultivation strategy furnished diversified nutritive platform in terms of homologous/heterologous plant organ-based medium and ambient/limited oxygenic cultivation procedure. Duly, cultivability extended to > 8 genera: Bosea, Brevundimonas, Chitinophaga, Pseudoxanthomonas, Sphingobacterium Caulobacter, Scandinavium, and Starkeya; the latter three genera were not yet reported for Sunflower, and possible unknown species or even one new putative genus. Thus, both potential members of the major microbiome and rare isolates of satellite microbiomes can be isolated using the presented method. It is a feasible addition to traditional cultivation methods to explore new potential resources of PGPB for future biotechnological applications.