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Rice grain number is a crucial agronomic trait impacting yield. In this study, we characterized a quantitative trait locus (QTL), GRAIN NUMBER 1.1 (GN1.1), which encodes a Flowering Locus T‐like1 (FT‐L1) protein and acts as a negative regulator of grain number in rice. The elite allele GN1.1B, derived from the Oryza indica variety, BF3‐104, exhibits a 14.6% increase in grain yield compared with the O. japonica variety, Nipponbare, based on plot yield tests. We demonstrated that GN1.1 interacted with and enhanced the stability of ADP‐ribosylation factor (Arf)‐GTPase‐activating protein (Gap), OsZAC. Loss of function of OsZAC results in increased grain number. Based on our data, we propose that GN1.1B facilitates the elevation of auxin content in young rice panicles by affecting polar auxin transport (PAT) through interaction with OsZAC. Our study unveils the pivotal role of the GN1.1 locus in rice panicle development and presents a novel, promising allele for enhancing rice grain yield through genetic improvement. [ABSTRACT FROM AUTHOR]

Auxin is a crucial phytohormone, controlling multiple aspects of plant growth and responses to the changing environment. However, the role of local auxin biosynthesis in specific developmental programs remains unknown in crops. This study characterized the rice tillering and small grain 1 (tsg1) mutant, which has more tillers but a smaller panicle and grain size resulting from a reduction in endogenous auxin. TSG1 encodes a tryptophan aminotransferase that is allelic to the FISH BONE (FIB) gene. The tsg1 mutant showed hypersensitivity to indole‐3‐acetic acid and the competitive inhibitor of aminotransferase, L‐kynurenine. TSG1 knockout resulted in an increased tiller number but reduction in grain number and size, and decrease in height. Meanwhile, deletion of the TSG1 homologs OsTAR1, OsTARL1, and OsTARL2 caused no obvious changes, although the phenotype of the TSG1/OsTAR1 double mutant was intensified and infertile, suggesting gene redundancy in the rice tryptophan aminotransferase family. Interestingly, TSG1 and OsTAR1, but not OsTARL1 and OsTARL2, displayed marked aminotransferase activity. Meanwhile, subcellular localization was identified as the endoplasmic reticulum, while phylogenetic analysis revealed functional divergence of TSG1 and OsTAR1 from OsTARL1 and OsTARL2. These findings suggest that TSG1 dominates the tryptophan aminotransferase family, playing a prominent role in local auxin biosynthesis in rice. [ABSTRACT FROM AUTHOR]

Heat stress poses a significant threat to grain yield. Our previous study identified TT1, which encodes an α2 subunit of the 26S proteasome, as a critical regulator for rice heat tolerance, representing the first cloned QTL for crop heat tolerance. However, the mechanisms mediated by TT1 still remained elusive. In this study, we unveil SUMO-conjugating enzyme 1 (SCE1), which interacts with TT1 and acts as a downstream component of TT1, engaging in the TT1-mediated 26S proteasome degradation. SCE1 functions as a negative regulator of heat tolerance and can be linked to ubiquitination modification. Additionally, we observed that sHSPs such as Hsp24.1 and Hsp40 can undergo SUMOylation mediated by SCE1, leading to increased accumulation of sHSPs in the absence of SCE1. Furthermore, we propose that the global SUMOylation modulated by SCE1 serves as a crucial signal in response to heat stress, and the rapid decline in elevated SUMOylation is considered a positive effect to enhance heat tolerance due to the loss of SCE1 gene function. Reducing protein levels of SCE1 significantly enhanced grain yield under high-temperature stress by improving seed-setting rate and rice grain filling capacity. Our results uncover the critical role of SCE1 in TT1-mediated heat tolerance pathway, regulating the abundance of sHSP proteins and SUMOylation, and ultimately impacting rice heat tolerance. These findings underscore the significant potential of the TT1-SCE1 module in improving the heat tolerance of crops., (Copyright © 2024 The Author. Published by Elsevier Inc. All rights reserved.)

Phosphoinositides (PIs) as regulatory membrane lipids play essential roles in multiple cellular processes. Although the exact molecular targets of PI-dependent modulation remain largely elusive, the effects of disturbed PI metabolism could be employed to identify regulatory modules associated with particular downstream targets of PIs. Here, we identified the role of GRAIN NUMBER AND PLANT HEIGHT1 ( GH1 ), which encodes a suppressor of actin (SAC) domain-containing phosphatase with unknown function in rice ( Oryza sativa ). Endoplasmic reticulum-localized GH1 specifically dephosphorylated and hydrolyzed phosphatidylinositol 4-phosphate (PI4P) and phosphatidylinositol 4,5-bisphosphate [PI(4,5)P 2 ]. Inactivation of GH1 resulted in massive accumulation of both PI4P and PI(4,5)P 2 , while excessive GH1 caused their depletion. Notably, superabundant PI4P and PI(4,5)P 2 could both disrupt actin cytoskeleton organization and suppress cell elongation. Interestingly, both PI4P and PI(4,5)P 2 inhibited actin-related protein2 and -3 (Arp2/3) complex-nucleated actin-branching networks in vitro, whereas PI(4,5)P 2 showed more dramatic effects in a dose-dependent manner. Overall, the overaccumulation of PI(4,5)P 2 resulting from dysfunction of SAC phosphatase possibly perturbs Arp2/3 complex-mediated actin polymerization, thereby disordering cell development. These findings imply that the Arp2/3 complex might be the potential molecular target of PI(4,5)P 2 -dependent modulation in eukaryotes, thereby providing insights into the relationship between PI homeostasis and plant growth and development., (© 2020 American Society of Plant Biologists. All Rights Reserved.)

As sessile organisms, plants have evolved numerous strategies to acclimate to changes in environmental temperature. However, the molecular basis of this acclimation remains largely unclear. In this study we identified a tRNA His guanylyltransferase, AET1, which contributes to the modification of pre-tRNA His and is required for normal growth under high-temperature conditions in rice. Interestingly, AET1 possibly interacts with both RACK1A and eIF3h in the endoplasmic reticulum. Notably, AET1 can directly bind to OsARF mRNAs including the uORFs of OsARF19 and OsARF23, indicating that AET1 is associated with translation regulation. Furthermore, polysome profiling assays suggest that the translational status remains unaffected in the aet1 mutant, but that the translational efficiency of OsARF19 and OsARF23 is reduced; moreover, OsARF23 protein levels are obviously decreased in the aet1 mutant under high temperature, implying that AET1 regulates auxin signaling in response to high temperature. Our findings provide new insights into the molecular mechanisms whereby AET1 regulates the environmental temperature response in rice by playing a dual role in tRNA modification and translational control., (Copyright © 2019 The Author. Published by Elsevier Inc. All rights reserved.)