Since the 1990s, the development of tagging methods has facilitated the isolation and identification of causative genes through the acquisition of loss-of-function mutants. However, a limitation of this approach was its inability to isolate genes with redundant functions. Therefore, I focused on gain-of-function mutants. In this study, numerous rice mutants were generated through activation tagging and Full-length cDNA OvereXpression (FOX), and the causal genes were subsequently isolated and characterized. The Spl18 mutant, which exhibits a lesion-mimic phenotype in the activation tagging lines, was found to result from the overexpression of an uncharacterized acyltransferase gene, OsAT1. The brassinosteroid (BR) biosynthetic gene, OsBR6ox, was the first BR biosynthetic gene isolated from monocots as the causal gene of the brd1 mutant, which exhibits a severe dwarf phenotype. Additionally BU1 and SG1 were found to positively and negatively regulate BR signaling, respectively. DPF, the causal gene of another lesion mimic mutant, was shown to regulate the transcription of diterpenoid phytoalexin biosynthetic genes. Furthermore, two BROAD-SPECTRUM RESISTANCE (BSR) genes were identified, which confer broad-spectrum disease resistance when overexpressed in multiple plant species. BSR1, which encodes a receptor-like cytoplasmic kinase, is involved in MAMP signaling, while BSR2, which encodes a cytochrome P450 protein, is associated with flower and seed size in addition to disease resistance.

Land plants have evolved to survive in terrestrial conditions. On the other hand, they lost the ability to live under prolonged submerged conditions. Some plants referred to as amphibious plants can thrive both in terrestrial and submerged conditions. They often show phenotypic plasticity to respond to fluctuating surrounding conditions. Under submerged condition, they emerge narrower and thinner than aerial leaves with low stomatal density. Furthermore, it has been suggested that ethylene is important for the response to submergence. The accumulation of ethylene triggers amphibious plants to cause physiological change. Although the mechanism of submergence response is not fully elucidated, recent analysis with omics techniques shed light on the molecular basis to adapt to fluctuating environments. In this review, we summarize the function of amphibious plants to survive underwater and the role of ethylene in submerged responses.

This study explores the mechanism of columnar tree formation in apples and its chemical regulation. Apple production in Japan is declining due to an aging workforce and labor-intensive tasks like pruning and harvesting. The columnar tree shape offers a potential solution by enabling compact growth, simplifying pruning, and allowing mechanized harvesting. The columnar shape originated from a natural mutation in McIntosh Wijcik. Genetic studies identified the Co gene as its key effector, with MdDOX-Co, which is a dioxygenase family enzyme, playing a crucial role. While normally expressed in roots, MdDOX-Co is also expressed in aerial parts in columnar apples, leading to abnormal growth. It inhibits gibberellin (GA) activation by hydroxylating GA at the C-12 position, causing shorter internodes and dwarfism. A chemical screening approach identified C4 as a selective MdDOX-Co inhibitor, allowing potential chemical control of tree morphology. This research contributes to the development of new apple varieties, such as Benitsurugi, introduced in 2024. By regulating MdDOX-Co, fruit coloration and yield may be further improved. These findings could also be applied to other fruit trees, offering a new strategy for enhancing productivity and sustainability in modern agriculture.

Temperature sensing is crucial for the survival of organisms. While animals use TRP channels as thermosensors, land plants lack these genes. Previous studies suggested the presence of TRP-like temperature-sensitive ion channels in plants, but their molecular identity was unknown. This study investigated the temperature-sensitive leaf-folding movement of Samanea saman and showed that chill-induced leaf-folding was associated with the swelling of motor cells at the base of the leaflet. This finding led us to investigate the temperature sensitivity of an outward-rectifying K+channel, SPORK2, which has been reported as an ion channel responsible for the nyctinastic (circadian-rhythmic) leaf movement of S. saman. As a result, we discovered that SPORK2 has a temperature-sensitive K+transport activity in Xenopus laevis oocytes. When expressed in Arabidopsis guard cells, SPORK2 induced temperature-dependent stomatal closure. These findings suggest that SPORK2 functions as a temperature-sensing molecule, similar to animal TRP channels, and advance our understanding of temperature-sensing mechanisms in plants.

While the molecular mechanisms by which plants respond to external nitrogen, such as nitrate, are recently well understood, those of responding to internal nitrogen to regulate plant physiological processes remain elusive. In root nodule symbiosis (RNS), iron is important for symbiotic nitrogen fixation, but how iron is accumulated in the nodules remains unclear. In this study, we focused on the internal nitrogen status during RNS in Lotus japonicus and revealed that LjIMA1/2 are expressed in shoots and roots and function both systemically and locally in the root. IMA is a small non-secreted peptide that promotes the iron deficiency response, and LjIMA1/2 play a role in accumulating iron in the nodules. Furthermore, LjIMA1/2 are also expressed in response to external nitrogen nutrients, contributing to the regulation of nitrogen homeostasis by adjusting the nitrogen-iron balance. These findings indicate the existence of a molecular mechanism linking iron- and nitrogen-related physiological processes through IMA peptides.

IAA carboxyl methyltransferase 1 (IAMT1) converts auxin (IAA) into its methyl ester (MeIAA). IAMT1 is reportedly critical for shoot development of Arabidopsis, but its metabolic role has remained unclear. We previously discovered auxin methylation during root nodule symbiosis in Lotus japonicus, and are currently investigating its metabolic role in this context. The symbiotic organ, the nodule, requires spatiotemporal regulation to accommodate rhizobia during its formation. Nodule formation involves bacterial infection of the root epidermis, followed by primordium formation in the adjacent layers root cortex, steps that must be spatiotemporally coordinated. While IAMT1 expression was induced in epidermis during infection, its function was required in cortex, where it promoted nodule development. This suggests a spatiotemporal role of IAMT1 across tissue layers. Endogenous MeIAA increased in roots after epidermal infection. Exogenous MeIAA, in combination with cytokinin, a key phytohormone in nodule primordium formation, was sufficient to induce organogenesis in rhizobia-susceptible zone in the absence of rhizobia. Our results could provide evidence for the role of auxin methylation in the spatial regulation of the site of organogenesis.

Plants response to inappropriate environmental conditions to survive. However, drought and high temperatures coursed by global boiling are serious problems for plant ecosystems, including forests and agriculture. We have discovered a novel survival mechanism mediated acetic acid against drought in plants and have developed technology to maintain plant resources. This review outlines plant stress response mechanisms, including epigenetically regulated acetic acid-mediated plant drought tolerance mechanisms, and show the technology for practical applications of the acetic acid-mediated drought and heat tolerances.