Tao Song

Asynchronous floret opening hinders hybrid rice seed production, particularly between indica and japonica subspecies. Although jasmonate (JA) signaling regulates diurnal floret opening time (DFOT), the mechanism underlying structural changes in the lodicule as a swellable organ driving floret opening remains unclear. Here, we identified OsbHLH091 as a lodicule-specific transcription factor mediating JA-induced floret opening. The null mutants of OsbHLH091 exhibit cleistogamy (closed flowers) without defects in floral organ, while OsbHLH091 overexpression accelerates floral opening. Mechanistically, OsbHLH091 activates cell expansion genes, including EXPANSINs and CELLULOSE SYNTHASEs, and such activity is repressed by JAZ proteins, the JA signaling inhibitors. Increasing JA before anthesis degrades JAZs, which releases OsbHLH091 to trigger lodicule expansion. Natural variation in OsbHLH091 contributes to DFOT differences between subspecies: the japonica haplotype interacts more strongly with JAZs, thus delaying opening. Together, as a lodicule-specific regulator, OsbHLH091 not only reveals a previously unknown mechanism controlling floret opening but also provides a precise tool to synchronize DFOT across subspecies, enabling efficient indica-japonica hybrid breeding.

The grain sorghum inbred line 654 serves as a parent for numerous Chinese commercial hybrids and recombinant inbred lines (RILs), which have played a pivotal role in the cloning of several agronomically important traits. In this study, we present a telomere-to-telomere (T2T) genome assembly of the inbred line 654 (728.81 Mb) using PacBio HiFi, ultra-long Oxford Nanopore Technology, and Hi-C sequencing data. The T2T genome assembly has high integrity (contains all of 10 centromeres and 20 telomeres without any gaps), high contiguity (contig N90: 52.02 Mb), high completeness (98.33% BUSCO completeness, 98.88% k-mer completeness, and LAI 24.38), and extremely low base error (3.37 × 10^-7, QV: 64.72). A total of 62.34% sequences were identified as repetitive, and rest region contained 44,399 protein-coding genes, of which 30,245 were functionally annotated. The gap-free T2T genome assembly enables the full picture of the potential translational genomics, and provides the highest resolution genetic map for future studies on genome evolution, structure variation, and the genetic control of agronomic traits in sorghum breeding.

Seed plants overtook ferns to become the dominant plant group during the late Carboniferous, a period in which the climate became colder and dryer^1,2. However, the specific innovations driving the success of seed plants are not clear. Here we report that the appearance of suberin lamellae (SL) contributed to the rise of seed plants. We show that the Casparian strip and SL vascular barriers evolved at different times, with the former originating in the most recent common ancestor (MRCA) of vascular plants and the latter in the MRCA of seed plants. Our results further suggest that most of the genes required for suberin formation arose through gene duplication in the MRCA of seed plants. We show that the appearance of the SL in the MRCA of seed plants enhanced drought tolerance through preventing water loss from the stele. We hypothesize that SL provide a decisive selective advantage over ferns in arid environments, resulting in the decline of ferns and the rise of gymnosperms. This study provides insights into the evolutionary success of seed plants and has implications for engineering drought-tolerant crops or fern varieties.

Functionally similar to the tight junctions present in animal guts, plant roots have evolved a lignified Casparian strip as an extracellular diffusion barrier in the endodermis to seal the root apoplast and maintain nutrient homeostasis. How this diffusion barrier is structured has been partially defined, but its lignin polymerization and assembly steps remain elusive. Here, we characterize a family of dirigent proteins (DPs) essential for both the localized polymerization of lignin required for Casparian strip biogenesis in the cell wall and for attachment of the strip to the plasma membrane to seal the apoplast. We reveal a Casparian strip lignification mechanism that requires cooperation between DPs and the Schengen pathway. Furthermore, we demonstrate that DPs directly mediate lignin polymerization as part of this mechanism.

Cell–cell junctions are essential for multicellular organisms to maintain nutrient homoeostasis. A plant-type tight junction, the Casparian strip (CS)–Casparian strip membrane domain (CSD) that seals the paracellular space between adjacent endodermal cells, has been known for more than one hundred years. However, the molecular basis of this structure remains unknown. Here we report that a new family of proteins containing a glycine/alanine/proline-rich domain, a lectin domain and a secretory signal peptide (GAPLESS) mediates tethering of the plasma membrane to the CS in rice. The GAPLESS proteins are specifically localized in the CS of root endodermal cells, and loss of their functions results in a disabled cell–cell junction and disrupted nutrient homoeostasis. The GAPLESS protein forms a tight complex with OsCASP1 in the plasma membrane, thereby mediating the CS–CSD junction. This study provides valuable insights into the junctional complex of plant endodermal cells, shedding light on our understanding of nutrient homoeostasis in crops and the cell junctions of eukaryotes.