Target of rapamycin (TOR) is a highly conserved serine/threonine-protein kinase among all eukaryotes. As a central regulator, TOR integrates nutrient, energy, growth factor and environmental signals to control cell proliferation, growth, and metabolism. With the establishment of TOR research systems in plants, tremendous progress has been made in, both conserved and unique functions of plant TOR have been uncovered in recent years. Here, we reviewed TOR complexes and the mechanisms of plant TOR integrating sugar, nitrogen, phosphate, sulfur, phytohormone and stress signals to orchestrate transcription, translation, metabolism, autophagy, and stress responses. We also highlight a few fundamental questions that will be of great interest to be resolved for fully revealing biofunctions of plant TOR.

A large area of membrane surface and intracellular immune receptors have been evolved in higher plants to sense various pathogen signals and prevent pathogen invasion. Among them, pattern recognition receptors on the cell surface activate basic immune response after sensing pattern molecules, while nucleotide-bounding leucine-rich repeat proteins (NLRs) activate specific immune response by sensing effector proteins secreted by pathogenic microorganisms, resulting in hypersensitivity and cell death. In this review, the latest research progress of plant immunity is mainly reviewed from the aspects of NLRs on the recognition of effector proteins, plant immune activation and downstream signal regulation.

Cryo-focused ion beam-scanning electron microscopy (Cryo-FIB-SEM) is an emerging technology designed for advanced imaging detection, which performs in situ by combining Cryo-FIB milling and Cryo-SEM imaging, and has facilitated the visualization of the native structures of biological sample in the context of the cellular environment in the frozen hydrated state. In recent years, a series of important advances have been achieved in the application of this technology in the research field of life science. In this review, we summarize its application in cryo-volume serial imaging, and in combination with cryo-correlative light and electron microscopy (CLEM), cryo-transmission SEM (TSEM), cryo-lamella preparation monitoring, and Cryo-SEM image processing. We also provide future prospective on future development and application of Cryo-FIB-SEM in three-dimensional in situ imaging of large volume biological samples.

Auxin is one of the most important plant hormones and plays a key role in regulating plant growth and development. In plants, early auxin responsive gene families, such as Aux/IAA (Auxin/Indole acetic acid repressors), GH3 (Gretchen Hagen3) and SAUR (Small Auxin up RNA), are rapidly induced and up-regulated by auxin treatment. Aux/IAA gene family is generally composed of four conserved domains. Domain I inhibits the expression of downstream genes in the auxin signaling pathway, and domain II is mainly regulated by Transport Inhibitor Response 1 (TIR1) in auxin signal transduction, thus affecting the stability of Aux/IAA. Domain III/IV regulates auxin signaling by interacting with Auxin Response Factor (ARF). Aux/IAA gene family has been reported to play an important role in organ development, root formation, stem elongation and leaf expansion in dicotyledonous Arabidopsis thaliana while in monocotyledonous rice (Oryza sativa) and wheat (Triticum aestivum), Aux/IAA mainly affects root development and plant architecture. However, the functions of most Aux/IAA genes remain unclear and need to further study. In this article, we reviewed the structure and function of Aux/IAA protein, and the auxin signal transduction pathway in Arabidopsis, cereal crops and other plants to provide clues for fully revealing the biofunction of the Aux/IAA gene family.

The recessive nuclear male sterility line is the base of the third-generation hybrid rice breeding technology. To explore new male sterility lines suitable for the breeding technology, we screened an ethyl methylsulfonate (EMS) mutant library derived from the elite xian variety Huanghuazhan (HHZ) and identified male sterility mutant 102 (ms102). The ms102 showed a normal vegetative development, but exhibited defective anther dehiscence and pollen abortion. Cytological analyses revealed that the degradation of the tapetum was abnormal in ms102, resulting in the abortion of microspores. Genetic analyses showed that the male sterile phenotype of ms102 was resulted from the mutation of a known male sterility gene Defective Pollen Wall 2 (DPW2), which encodes an acyl transferase. Thus, this study identified a recessive nuclear male sterility mutant, and further confirmed the function of DPW2 in rice pollen development.

MBF1 (multiprotein bridging factor 1) is a transcriptional co-activator, which is highly conserved in evolution. It exists in all eukaryotes and can activate gene transcription by connecting components of the basal transcription machinery and transcription factors. Plant MBF1 plays important roles in a variety of biological processes, including controlling plant growth and development, and adversity adaptation. This review demonstrates the advance in the molecular structure and regulation mechanism of plant MBF1, and highlights the molecular mechanism of AtMBF1c in the regulation of plant heat stress response.

Precise regulation of floral transition, which ensures plants bloom in the suitable environment, is essential for the successful reproduction of plants. The flowering time genes are regulated by a variety of molecular mechanisms, including transcriptional, post-transcriptional and post-translational regulations. Alternative splicing is a universal molecular process at the post-transcriptional level that can generate multiple transcripts from a single gene, thereby enriching the diversity of the transcriptome and proteome. The accumulating evidence indicates that alternative splicing plays an important role in the floral transition. According to developmental and environmental cues, alternative splicing can regulate the levels of functional transcripts and/or proteins of flowering time genes by affecting the stability of mRNA and/or the function of protein isoforms. Therefore, revealing the roles of alternative splicing will further improve our understanding of the functions of flowering time genes and the whole regulatory network of floral transition. In this review, we introduce the research progress of alternative splicing in floral transition, and summarize from the various regulatory pathways, thereby providing a reference for further research on the regulatory mechanisms of alternative splicing and floral transition in plants.

The nucleolus is a key structure in the nucleus of eukaryotic cells. Ribosome biogenesis initially takes place in the nucleolus, which involves a series of complex reactions and requires the participation of many nucleolus-associated factors. Abnormal ribosome biogenesis usually leads to disordered nucleolus structure, cell cycle arrest, cell senescence, and even cell death. The mechanism of ribosomal stress response has been studied well in mammals, while it remains largely unknown in plant cells. Nevertheless, it has been found that members of the plant-specific NAC transcription factor family are involved in various intracellular stress responses, including ribosomal stress, in plant cells. In addition, we previously reported a coordination mechanism between auxin system and ribosome biogenesis for modulating plant development. In this review, we discussed potential mechanisms of ribosome stress response in plant cells through combining the knowledge of ribosomal stress response pathways in mammals.

Hyperhydricity (HH) or vitrification is a physiological disorder during plant growth, which shows a typical translucent phenotype like water-soaked that often occurs in the plant tissue culture. Vitrification is one of the three main influencing factors that limit the tissue culture technology and the commercialized production of seedlings during the plant tissue culture, but its molecular mechanism is still unclear by far. Using plantlets from the tissue culture as a research object often lead to an interference of man-made factors, which can be avoided by non-tissue culture material to reveal the molecular mechanism of vitrification in nature. This review summarized the recent progress of mechanism for inducing HH in non-tissue culture plants, including the abnormal deposit of suberin, the reduction of cuticular wax, the lipid peroxidation in cellular membranes and the disrupted transmembrane transport of ion or water, to provide new clues and thinking for hyperhydricity in plant seedling growth.

The optical clearing techniques are common methods that allow biological tissues or organs to be deeply transparent and imaged under an optical microscope by processing with chemical reagents. Driven by a variety of optical microscopy technologies, the entire tissue can be imaged and reconstructed three-dimensionally (3D) using the clearing technique to deeply analyze the internal spatial characteristics and formation mechanism of biological tissues. In recent years, several optical clearing techniques and multi-scale imaging techniques have been developed and fruitful researches have been reported. This article discusses basic principles and some new techniques of optical clearing, with particular focus on new imaging methods based on optical clearing technique and their applications in plant imaging and cell biology. This review will provide theoretical basis and technical support for the subsequent research on clearing, imaging and 3D reconstruction and function of whole plants, tissues or organs.

Melatonin (N-acetyl-5-methoxytryptamine) is a small molecule indoleamine that is essential for life. Melatonin is widely present in animals and plants, and plays a vital role in the growth and development. With the study of plant melatonin, its synthesis pathway and roles in plants have become clear. Studies have shown that melatonin has the regulatory effects in improving plant resistance to abiotic and biotic stresses. This review summarizes the research progress of melatonin in plant abiotic and biotic stresses in recent years; it provides reference for in-depth analysis of influence of melatonin on the regulation mechanism of plant resistance to stresses.

Nihewan Basin in North China is endowed with ‘the Olduvai Gorge in East Africa'. Both basins have a similar geological evolution with well-developed fluvial and lacustrine deposits, rich fossil and a large number of remains of early humans. Undoubtedly, it is a key area to study the changes of habitats of early humans in East Asia. Compiling the literatures, we sketched the changes in vegetation, climate and early human habitats in the Nihewan Basin since the late Pliocene and noticed that the first vegetation shift from broad-leaved forest to coniferous forest occurred at ~2.6 Ma (Mega annum); the second important change of vegetation succession occurred at about 1.92 Ma. After that time, the vegetation was mainly temperate forest-steppe (covering Pinus, Artemisia, Chenopodiaceae)/temperate steppe (mainly Artemisia and Poaceae). By comparison, it is found that the vegetation change from forest to forest-steppe appeared gradually from west to central throughout northern China since the late Pliocene. In addition, at least 13 cold-warm cycles and 15 dry-wet cycles were recorded. Significant cold-dry events occurred at 2.8 Ma, 2.6 Ma, 1.92 Ma, and 143.8 ka (kilo annum), while humid events took place at 43, 32, and 6.6 ka. Early humans lived in forest-steppe or steppe environment with rich water resources where cold-warm and dry-wet climate fluctuated periodically, and co-existed with other mammals. In the future, under the chronological framework of establishing a more fine stratum of Nihewan human site, quantitative research on temperature and precipitation parameters of paleoclimate will benifit accurate reconstruction of the habitat of hominins and reflection of the law of change.