In the past decade, root biology achieved significant accomplishments remarkably advancing our knowledge on the molecular mechanisms for morphogenesis including tissue and organ differentiation, and responses to environmental cues.　Here, we emphasize recent developments that revealed novel regulatory mechanisms of root cap differentiation, lateral root formation, and tropisms in roots.

Plant tropisms have fascinated plant biologists since the early work of Charles and Francis Darwin.　Today, it is well known that the tropisms play important role in formation of plant architecture to gain environmental resource such as light, water and nutrients, effectively.　In gravitropism, stems grow upward and roots elongate toward downward.　It has been critical challenge to understand how plants sense the direction of gravity and convert it into biochemical signal.　This review focuses on recent advance in gravity sensing mechanisms.　Then, we introduce the identification and molecular function of LAZY1 family genes as a factor involved in gravity signaling process.　Finally, we discuss the contribution of gravitropism on the regulation of growth angle in lateral organs that the mechanism leads to the determination of entire plant architecture.

Roots of land plants show gravitropism and hydrotropism in response to gravity and moisture gradients, respectively, for controlling their growth orientation.　It has been shown that in Arabidopsis roots MIZ1 and MIZ2, as well as ABA, play critical roles in hydrotropic response.　Both MIZ1 and ABA responses occur in cortex of the elongation zone.　Auxin negatively regulates hydrotropism in Arabidopsis roots.　On the other hand, auxin transport and redistribution are required for hydrotropic response of cucumber roots.　However, the root cap is dispensable for the induction of hydrotropism in both Arabidopsis and cucumber roots.　These results imply that regulatory mechanisms unique to root hydrotropism exist and that the mechanisms differ among plant species.　This review describes recent development of research on root hydrotropism, with special references to regulatory genes and molecules, signaling systems, and species differences.

Root caps are commonly found at the tip of plant roots.　Root caps not only serve as a physical protectant of the root meristem, but also execute a wide variety of physiological functions important for root and shoot growth, such as gravity-sensing, lubrication, and rhizosphere interaction.　While the knowledge on root cap functions has been obtained mostly from crop species such as pea and maize, which have thick roots and thus are suitable for root tip handling, recent molecular genetics and imaging analyses of the model plant Arabidopsis thaliana have identified key factors regulating root cap differentiation, as well as those implementing root cap-specific functions and cellular dynamics.　These studies now started to address how this complex plant tissue is generated and how its physiological functions are executed at genetic and molecular levels.　In this review, I first introduce current knowledge on basic structures and developmental regulation of root caps, and then discuss how the structures and cellular dynamics unique to the root caps contribute to their specific functions, as well as to optimizing root development and plant growth.

Lateral root（LR）formation in most vascular plants is initiated by asymmetric division of founder cells, followed by coordinated cell proliferation and differentiation for patterning new primordia.　The sequential developmental processes of LR formation are triggered by a localized auxin response.　In Arabidopsis, LATERAL ORGAN BOUNDARIES‐DOMAIN 16 （LBD16）, an auxin‐inducible transcription factor, is one of the key regulators linking auxin response in LR founder cells to LR initiation.　This review summarizes recent findings on LR formation, focusing on the molecular mechanisms of auxin/LBD16-regulated LR initiation and lateral inhibition of LR founder cell formation.

Cytokinin is a classical phytohormone discovered approximately 65 years ago.　Cytokinin was first shown to promote cell division and subsequently determined to play a key role in regulating a wide variety of aspects in plant growth and development.　Studies of cytokinin biosynthesis and its actions in the past 20 years have revealed a basic frame of cytokinin biosynthesis in plants and some phytopathogens, as well as the biological significance of its structural variations.　These findings have provided valuable information for understanding the mechanisms underlying proper plant growth regulation in response to environmental changes and niche formation strategies of some plant pathogens.

It has been more than half a century since abscisic acid （ABA） was isolated and identified in the 1960s as a substance that promotes the abscission of cotton fruits and as a growth inhibitor related to dormancy of maple buds.　On the other hand, only 10 years have passed since the identification of the ABA receptor.　However, during this short period of time, research on ABA receptors has been actively conducted from various points of view, and it has become possible to draw detailed and wide-ranging views of ABA perception and signal transduction.　In this review, we would like to introduce the present knowledge about the factors that regulate the function of ABA receptors and their mechanisms, including the results of our research.

The set and growth of eggplant fruits can be improved by using insect pollinators or by treating flowers with phytohormones.　These techniques can be costly and labor-intensive.　Parthenocarpic cultivars offer the most cost-effective solution to improving fruit set and growth under suboptimal conditions.　‘Anominori 2 go’, a parthenocarpic eggplant cultivar developed at the NARO Institute of Vegetable and Tea Science in 2011, is an F1 hybrid between two parthenocarpic inbred lines, ‘AE-P01’ and ‘AE-P24’.　‘AE-P01’ was selected from a cross between ‘Talina’ （a commercial parthenocarpic F1 hybrid that was widely cultivated in Italy） and ‘Nasu Chukanbohon No 1 go’ （a Japanese parental line）.　‘AE-P24’ was developed from selective crossing of ‘Nakate Shinkuro’ （a Japanese traditional cultivar）, ‘Talina’, ‘Nasu Chukanbohon No 1 go’, and ‘Senryo Nigo’ （a commercial F1 hybrid that is widely cultivated in Japan）.　‘Anominori 2 go’ produces commercial fruits without phytohormone treatment;yields are higher than those of ‘Anominori’, another parthenocarpic cultivar developed at our institute.

MLX56 family defense proteins, MLX56 and its close homolog LA-b, are chitin-binding defense proteins found in mulberry latex that show strong growth-inhibitions against caterpillars when fed at concentrations as low as 0.01%.　MLX56 family proteins contain a unique structure with an extensin domain surrounded by two hevein-like chitin-binding domains and have totally unique mode of defensive action against insects.　Experimental results suggest that MLX56 family proteins, through their chitin-binding domains, bind to the chitin framework of the peritrophic membrane （PM:a thin membrane consisting of chitin that wraps food materials in the midgut lumen of insects）, then through their extensin-domain （gum arabic-like structure）, which functions as swelling agent, swells PM into an abnormally thick membrane that inhibits the digestive processes and growth of insects.　Plants expressing mlx56 gene （MLX56 protein） showed strong resistances to various pests including Spodoptera litura, Mamestra brassicae, Plutella xylostella （Lepidoptera）, and other pests belonging to Coleoptera （ladybirds） and Thysanoptera （thrips）, suggesting that MLX56 is a promising substitute of Bt toxin in making pest-resistant plants in future.

Seed germination and establishment of seedlings are crucial for agriculture.　High quality seeds of every crop are demanded in the seed market.　Seed treatment techniques are one of the most important solutions to deal with this situation.　Seed treatments consist of seed coating, disinfection and seed enhancement techniques.　This article is intended to introduce the seed treatments techniques which are basic and essential in the seed industry.