Photosynthetic performance of glumes of oat spikelets is more stable for grain-filling stage under drought stress.

Drought stress affects plant photosynthesis, leading to a reduction in the quality and yield of crop production. Non-foliar organs play a complementary role in photosynthesis during plant growth and development and are important sources of energy. However, there are limited studies on the performance of non-foliar organs under drought stress. The photosynthetic-responsive differences of oat spikelet organs (glumes, lemmas and paleas) and flag leaves to drought stress during the grain-filling stage were examined. Under drought stress, photosynthetic performance of glume is more stable. Intercellular CO2 concentration (Ci), chlorophyll b, maximum photochemical efficiency of photosystem II. (Fv/Fm), and electron transport rate (ETR) were significantly higher in the glume compared to the flag leaf. The transcriptome data revealed that stable expression of the RCCR gene under drought stress was the main reason for maintaining higher chlorophyll content in the glume. Additionally, no differential expression genes (DEGs) related to Photosystem Ⅰ (PSI) reaction centers were found, and drought stress primarily affects the Photosystem II (PSII) reaction center. In spikelets, the CP43 and CP47 subunits of PSII and the AtpB subunit of ATP synthase were increased on the thylakoid membrane, contributing to photosynthetic stabilisation of spikelets as a means of supplementing the limited photosynthesis of the leaves under drought stress. The results enhanced understanding of the photosynthetic performance of oat spikelet during the grain-filling stage, and also provided an important basis on improving the photosynthetic capacity of non-foliar organs for the selection and breeding new oat varieties with high yield and better drought resistance.

Engineering brassinosteroids pathway: a key strategy for enhancing crop yields.

KEY MESSAGE: Two significant studies have unveiled the pivotal role of BR regulation in shaping distinct features: the clustered-spikelet architecture in rice and the superior semi-dwarf stature in wheat.

OsPRMT6a-mediated arginine methylation of OsJAZ1 regulates jasmonate signaling and spikelet development in rice.

Although both protein arginine methylation (PRMT) and jasmonate (JA) signaling are crucial for regulating plant development, the relationship between these processes in the control of spikelet development remains unclear. In this study, we used the CRISPR/Cas9 technology to generate two OsPRMT6a loss-of-function mutants that exhibit various abnormal spikelet structures. Interestingly, we found that OsPRMT6a can methylate arginine residues in JA signal repressors OsJAZ1 and OsJAZ7. We showed that arginine methylation of OsJAZ1 enhances the binding affinity of OsJAZ1 with the JA receptors OsCOI1a and OsCOI1b in the presence of JAs, thereby promoting the ubiquitination of OsJAZ1 by the SCFOsCOI1a/OsCOI1b complex and degradation via the 26S proteasome. This process ultimately releases OsMYC2, a core transcriptional regulator in the JA signaling pathway, to activate or repress JA-responsive genes, thereby maintaining normal plant (spikelet) development. However, in the osprmt6a-1 mutant, reduced arginine methylation of OsJAZ1 impaires the interaction between OsJAZ1 and OsCOI1a/OsCOI1b in the presence of JAs. As a result, OsJAZ1 proteins become more stable, repressing JA responses, thus causing the formation of abnormal spikelet structures. Moreover, we discovered that JA signaling reduces the OsPRMT6a mRNA level in an OsMYC2-dependent manner, thereby establishing a negative feedback loop to balance JA signaling. We further found that OsPRMT6a-mediated arginine methylation of OsJAZ1 likely serves as a switch to tune JA signaling to maintain normal spikelet development under harsh environmental conditions such as high temperatures. Collectively, our study establishes a direct molecular link between arginine methylation and JA signaling in rice.

Non-cell-autonomous signaling associated with barley ALOG1 specifies spikelet meristem determinacy.

Inflorescence architecture and crop productivity are often tightly coupled in our major cereal crops. However, the underlying genetic mechanisms controlling cereal inflorescence development remain poorly understood. Here, we identified recessive alleles of barley (Hordeum vulgare L.) HvALOG1 (Arabidopsis thaliana LSH1 and Oryza G1) that produce non-canonical extra spikelets and fused glumes abaxially to the central spikelet from the upper-mid portion until the tip of the inflorescence. Notably, we found that HvALOG1 exhibits a boundary-specific expression pattern that specifically excludes reproductive meristems, implying the involvement of previously proposed localized signaling centers for branch regulation. Importantly, during early spikelet formation, non-cell-autonomous signals associated with HvALOG1 expression may specify spikelet meristem determinacy, while boundary formation of floret organs appears to be coordinated in a cell-autonomous manner. Moreover, barley ALOG family members synergistically modulate inflorescence morphology, with HvALOG1 predominantly governing meristem maintenance and floral organ development. We further propose that spatiotemporal redundancies of expressed HvALOG members specifically in the basal inflorescence may be accountable for proper patterning of spikelet formation in mutant plants. Our research offers new perspectives on regulatory signaling roles of ALOG transcription factors during the development of reproductive meristems in cereal inflorescences.

Rice myo-inositol-3-phosphate synthase 2 (RINO2) alleviates heat injury-induced impairment in pollen germination and tube growth by modulating Ca2+ signaling and actin filament cytoskeleton.

Low phytic acid (lpa) crop is considered as an effective strategy to improve crop nutritional quality, but a substantial decrease in phytic acid (PA) usually has negative effect on agronomic performance and its response to environment adversities. Myo-inositol-3-phosphate synthase (MIPS) is the rate-limiting enzyme in PA biosynthesis pathway, and regarded as the prime target for engineering lpa crop. In this paper, the rice MIPS gene (RINO2) knockout mutants and its wild type were performed to investigate the genotype-dependent alteration in the heat injury-induced spikelet fertility and its underlying mechanism for rice plants being imposed to heat stress at anthesis. Results indicated that RINO2 knockout significantly enhanced the susceptibility of rice spikelet fertility to heat injury, due to the severely exacerbated obstacles in pollen germination and pollen tube growth in pistil for RINO2 knockout under high temperature (HT) at anthesis. The loss of RINO2 function caused a marked reduction in inositol and phosphatidylinositol derivative concentrations in the HT-stressed pollen grains, which resulted in the strikingly lower content of phosphatidylinositol 4,5-diphosphate (PI (4,5) P2) in germinating pollen grain and pollen tube. The insufficient supply of PI (4,5) P2 in the HT-stressed pollen grains disrupted normal Ca2+ gradient in the apical region of pollen tubes and actin filament cytoskeleton in growing pollen tubes. The severely repressed biosynthesis of PI (4,5) P2 was among the regulatory switch steps leading to the impaired pollen germination and deformed pollen tube growth for the HT-stressed pollens of RINO2 knockout mutants.

The genetic basis and process of inbreeding depression in an elite hybrid rice.

Inbreeding depression refers to the reduced performance arising from increased homozygosity, a phenomenon that is the reverse of heterosis and exists among plants and animals. As a natural self-pollinated crop with strong heterosis, the mechanism of inbreeding depression in rice is largely unknown. To understand the genetic basis of inbreeding depression, we constructed a successive inbreeding population from the F2 to F4 generation and observed inbreeding depression of all heterotic traits in the progeny along with the decay of heterozygosity in each generation. The expected depression effect was largely explained by 13 QTLs showing dominant effects for spikelets per panicle, 11 for primary branches, and 12 for secondary branches, and these loci constitute the main correlation between heterosis and inbreeding depression. However, the genetic basis of inbreeding depression is also distinct from that of heterosis, such that a biased transmission ratio of alleles for QTLs with either dominant or additive effects in four segregation distortion regions would result in minor effects in expected depression. Noticeably, two-locus interactions may change the extent and direction of the depression effects of the target loci, and overall interactions would promote inbreeding depression among generations. Using an F2:3 variation population, the actual performance of the loci showing expected depression was evaluated considering the heterozygosity decay in the background after inbreeding. We found inconsistent or various degrees of background depression from the F2 to F3 generation assuming different genotypes of the target locus, which may affect the actual depression effect of the locus due to epistasis. The results suggest that the genetic architecture of inbreeding depression and heterosis is closely linked but also differs in their intrinsic mechanisms, which expand our understanding of the whole-genome architecture of inbreeding depression.

Micrometeorological monitoring reveals that canopy temperature is a reliable trait for the screening of heat tolerance in rice.

Micrometeorological monitoring is not just an effective method of determining the impact of heat stress on rice, but also a reliable way of understanding how to screen for heat tolerance in rice. The aim of this study was to use micrometeorological monitoring to determine varietal differences in rice plants grown under two weather scenarios-Long-term Heat Scenario (LHS) and Normal Weather Scenario (NWS)- so as to establish reliable methods for heat tolerance screening. Experiments were conducted with two heat susceptible varieties-Mianhui 101 and IR64-and two heat tolerant varieties, Quanliangyou 681 and SDWG005. We used staggered sowing method to ensure that all varieties flower at the same time. Our results showed that heat tolerant varieties maintained lower canopy temperature compared to heat susceptible varieties, not just during the crucial flowering period of 10 am to 12 pm, but throughout the entire day and night. The higher stomatal conductance rate observed in heat tolerant varieties possibly decreased their canopy temperatures through the process of evaporative cooling during transpiration. Conversely, we found that panicle temperature cannot be used to screen for heat tolerance at night, as we observed no significant difference in the panicle temperature of heat tolerant and heat susceptible varieties at night. However, we also reported that higher panicle temperature in heat susceptible varieties decreased spikelet fertility rate, while low panicle temperature in heat tolerant varieties increased spikelet fertility rate. In conclusion, the results of this study showed that canopy temperature is probably the most reliable trait to screen for heat tolerance in rice.

HOMEOBOX2, the paralog of SIX-ROWED SPIKE1/HOMEOBOX1, is dispensable for barley spikelet development.

The HD-ZIP class I transcription factor Homeobox 1 (HvHOX1), also known as Vulgare Row-type Spike 1 (VRS1) or Six-rowed Spike 1, regulates lateral spikelet fertility in barley (Hordeum vulgare L.). It was shown that HvHOX1 has a high expression only in lateral spikelets, while its paralog HvHOX2 was found to be expressed in different plant organs. Yet, the mechanistic functions of HvHOX1 and HvHOX2 during spikelet development are still fragmentary. Here, we show that compared with HvHOX1, HvHOX2 is more highly conserved across different barley genotypes and Hordeum species, hinting at a possibly vital but still unclarified biological role. Using bimolecular fluorescence complementation, DNA-binding, and transactivation assays, we validate that HvHOX1 and HvHOX2 are bona fide transcriptional activators that may potentially heterodimerize. Accordingly, both genes exhibit similar spatiotemporal expression patterns during spike development and growth, albeit their mRNA levels differ quantitatively. We show that HvHOX1 delays the lateral spikelet meristem differentiation and affects fertility by aborting the reproductive organs. Interestingly, the ancestral relationship of the two genes inferred from their co-expressed gene networks suggested that HvHOX1 and HvHOX2 might play a similar role during barley spikelet development. However, CRISPR-derived mutants of HvHOX1 and HvHOX2 demonstrated the suppressive role of HvHOX1 on lateral spikelets, while the loss of HvHOX2 does not influence spikelet development. Collectively, our study shows that through the suppression of reproductive organs, lateral spikelet fertility is regulated by HvHOX1, whereas HvHOX2 is dispensable for spikelet development in barley.

Simplified panicle fertilization is applicable to japonica cultivars, but splits are preferred in indica rice for a higher paddy yield under wheat straw return.

Introduction: The panicle fertilization strategy for japonica and indica rice under wheat straw return (SR) has not been updated, especially on the elaboration of their impacts on spikelet differentiation and degeneration. This study aimed to verify the hypothesis that SR increases spikelet number by reducing spikelet degeneration and to explore the possibility of simplifying panicle fertilization. Methods: In three consecutive years, four varieties of japonica and indica rice were field-grown in Yangzhou, Jiangsu Province, China. Six panicle fertilization rates and split treatments were applied to SR and no straw return (NR) conditions. Results: The results showed that SR promoted rice yield significantly by 3.77%, and the highest yields were obtained under the T2 (split panicle fertilization at the panicle initiation (PI) and spikelet primordium differentiation (SPD) stages) and T1 (panicle fertilization only at the PI stage) treatments, for indica and japonica rice, respectively. Correlation and path analysis revealed that the number of spikelets per panicle was the most attributable to yield variation. SR significantly increased the concentration of alkali hydrolyzable N in the soil 40 days after rice transplantation, significantly increased the nitrogen accumulation per stem (NA) during the SPD-pollen mother cell meiosis (PMC) stage, and increased the brassinosteroids level in the young panicles at the PMC stage. SR also reduced the degeneration rate of spikelets (DRS) and increased the number of surviving spikelets (NSS). The dry matter accumulation per stem was more important to increasing the NA in japonica rice at the PMC stage, whereas NA was more affected by the N content than the dry matter accumulation in indica rice. In japonica rice, panicle N application once only at the PI stage combined with the N released from SR was enough to improve the plant N content, reduce the DRS, and increase the NSS. For indica rice, split application of N panicle fertilization at both the PI and SPD stages was still necessary to achieve a maximum NSS. Discussion: In conclusion, under wheat SR practice, panicle fertilization could be simplified to once in japonica rice with a significant yield increase, whereas equal splits might still be optimal for indica rice.

Anatomical insights into the vascular layout of the barley rachis: implications for transport and spikelet connection.

BACKGROUND AND AIMS: Vascular patterning is intimately related to plant form and function. Here, using barley (Hordeum vulgare) as a model, we studied the vascular anatomy of the spike-type inflorescence. The main aim of the present work was to clarify the relationship between rachis (spike axis) vasculature and spike size, to define vascular dynamics and to discuss the implications for transport capacity and its interaction with the spikelets. METHODS: We used serial transverse internode sections to determine the internode area, vascular area and number of veins along the rachis of several barley lines. KEY RESULTS: Internode area and total vascular area show a clear positive correlation with spike size, whereas the number of veins is only weakly correlated. The lateral periphery of the rachis contains large mature veins of constant size, whereas the central part is occupied by small immature veins. Spikelet-derived veins entering the rachis often merge with the immature rachis veins but never merge with the mature veins. An increase in floret fertility through the conversion of a two-rowed barley into an isogenic six-rowed line, in addition to a decrease in floret fertility owing to enhanced pre-anthesis tip degeneration caused by the mutation tip sterile 2.b (tst2.b), significantly affected vein size but had limited to no effects on the number of veins or internode area. CONCLUSIONS: The rachis vasculature is the result of a two-step process involving an initial layout followed by size adjustment according to floret fertility/spike size. The restriction of large mature vessels to the periphery and that of small immature vessels to the centre of the rachis suggests that long-distance transport and local supply to spikelets are spatially separated processes. The identification of spikelet-derived veins entering the rachis without fusing with its vasculature indicates that a vascular continuity between rachis and spikelets might be non-essential.

First Report of Curvularia plantarum Causing Rice Spikelet Rot Disease in China.

In September 2022, rice spikelets rot disease (RSRD) was investigated in Songjiang District (30.94132N, 121.18393E), China, leading to a 26.77% yield loss. At the heading stage, infected spikelets exhibited small, yellowish-brown dots with water-stained husks, subsequently coalescing to form irregular brown to black lesions. Later, the lesions were enlarged and rotted, which eventually caused blighted grains. About 10% of husked grains showed black spots. 30 infected grains and 30 husked grains with black spots were surface sterilized in 75% ethanol for 2 min, then rinsed with ddH2O and plated on PDA medium at 28°C in darkness for 4 d. 22 and 13 fungal isolates with similar morphology were obtained in shriveled and husked grains, respectively. Three isolates (SJTU1, SJTU2 and SJTU3) were selected by the single-spore isolation method. The colonies were brown to blackish green, smooth, and contained a large number of stolons with a few aerial mycelia in the center. Hyphae and conidiophores were blackish green, thick-walled, branched with septa. Conidia were 14.77 to 26.82×4.74 to 11.36 µm (average 20.42×8.58 µm, n= 100) in size, lightly curved with blackish green. Conidia with three septa and four cells, apical and basal cells transparent, middle cell unequal in size. Based on morphological characteristics, the isolates were preliminarily identified as Curvularia plantarum (Raza et al. 2019). The genomic DNA of the three isolates (SJTU1 to 3) was extracted for molecular identification. 3 pairs of primers ITS1/TTS4 (Peever et al. 2004), gpd1/gpd2 (Berbee et al. 1999), and EF-983F/EF-2218R (Rehner and Buckley 2005) were used to amplify ITS, GAPDH, and EF1-α genes, respectively. These sequences were all uploaded in GenBank (ITS: OR726053 to 55; EF1-α: OR732471 to 73; GAPDH: OR732474 to 76). According to data in GenBank, the ITS, EF1-α, and GAPDH genes of 3 isolates (SJTU1 to 3) showed 99-100% identity (573/575 bp, 542/543 bp, and 531/531 bp) to the ITS (MW581905, MN044755, and MN215690), 99-100% identity (869/869 bp, 868/869 bp, and 855/856 bp) to the EF1-α (MN263982 to 83, and MT628901), and 99-100% identity (543/544 bp, 528/528 bp, and 540/540 bp) to the GAPDH (MT628902, MN264120, and MT432926) gene of C. plantarum, respectively. The phylogenetic analysis by Maximum Likelihood (ML) method based on the concatenated sequences of ITS, EF1-α, and GAPDH genes showed that the three isolates (SJTU1 to 3) clustered with C. plantarum. According to morphology and molecular identification, these fungal isolates were identified as C. plantarum. Pathogenicity tests were conducted in the field used only for inoculation with pathogens by spraying 30 spikelets of rice cultivar 'Song1013' at the heading stage with conidial suspension (5 × 105 conidia/mL). 30 spikelets sprayed with ddH2O were designated as control. The test was conducted 3 times at 22 to 31°C with 78 to 89% RH. All the inoculated spikelets exhibited similar symptoms to those of the infected spikelets in paddy at 10 d after spraying, while the control spikelets remained healthy. All reisolated strains from infected spikelets were identified the same as the original inoculated strains by morphology and ITS sequences, fulfilling Koch's postulates. To our knowledge, this is the first report of C. plantarum causing RSRD in China. The discovery of this new disease and its pathogens will facilitate the provision of pathogenically relevant information vital for management strategies to RSRD caused by C. plantarum in the future.

Identification and map-based cloning of long glume mutant gene lgm1 in barley.

The spikes of gramineous plants are composed of specialized units called spikelets. Two bracts at the spikelet bases are known as glumes. The spikelet glumes in barley are degenerated into threadlike structures. Here, we report a long glume mutant, lgm1, similar in appearance to a lemma with a long awn at the apex. Map-based cloning showed that the mutant lgm1 allele has an approximate 1.27 Mb deletion of in chromosome 2H. The deleted segment contains five putative high-confidence genes, among which HORVU.MOREX.r3.2HG0170820 encodes a C2H2 zinc finger protein, an ortholog of rice NSG1/LRG1 and an important candidate for the Lgm1 allele. Line GA01 with a long glume and short awn was obtained in progenies of crosses involving the lgm1 mutant. Interestingly, lsg1, a mutant with long glumes on lateral spikelets, was obtained in the progenies of the lgm1 mutant. The long glume variant increased the weight of kernels in the lateral spikelets and increased kernel uniformity across the entire spike, greatly improving the potential of six-rowed barley for malting. Supplementary Information: The online version contains supplementary material available at 10.1007/s11032-024-01448-x.

Low sucrose availability reduces basal spikelet fertility by inducing abscisic acid and jasmonic acid synthesis in wheat.

Within a spike of wheat, the central spikelets usually generate three to four fertile florets, while the basal spikelets generate zero to one fertile floret. The physiological and transcriptional mechanism behind the difference in fertility between the basal and central spikelets is unclear. This study reports a high temporal resolution investigation of transcriptomes, number and morphology of floret primordia, and physiological traits. The W6.5-W7.5 stage was regarded as the boundary to distinguish between fertile and abortive floret primordia; those floret primordia reaching the W6.5-W7.5 stage during the differentiation phase (3-9 d after terminal spikelet stage) usually developed into fertile florets in the next dimorphism phase (12-27 d after terminal spikelet stage), whereas the others aborted. The central spikelets had a greater number of fertile florets than the basal spikelets, which was associated with more floret primordia reaching the W6.5-W7.5 stage. Physiological and transcriptional results demonstrated that the central spikelets had a higher sucrose content and lower abscisic acid (ABA) and jasmonic acid (JA) accumulation than the basal spikelets due to down-regulation of genes involved in ABA and JA synthesis. Collectively, we propose a model in which ABA and JA accumulation is induced under limiting sucrose availability (basal spikelet) through the up-regulation of genes involved in ABA and JA synthesis; this leads to floret primordia in the basal spikelets failing to reach their fertile potential (W6.5-W7.5 stage) during the differentiation phase and then aborting. This fertility repression model may also regulate spikelet fertility in other cereal crops and potentially provides genetic resources to improve spikelet fertility.

Involvement of brassinosteroids and abscisic acid in spikelet degeneration in rice under soil drying during meiosis.

Spikelet degeneration in rice (Oryza sativa L.) is a serious physiological defect, and can be regulated by soil moisture status and phytohormones. This study investigated the possibility that brassinosteroids (BRs) in collaboration with abscisic acid (ABA) are involved in mediating the effect of soil drying during meiosis on spikelet degeneration in rice. Three rice cultivars were field grown and three irrigation regimes including well watered (WW), moderate soil drying (MD), and severe soil drying (SD) were imposed during meiosis. MD significantly decreased spikelet degeneration in comparison with WW, due mainly to the alleviation in oxidative damage via enhancing ascorbate-glutathione (AsA-GSH) cycle activity in young panicles, and SD exhibited the opposite effects. Enhanced AsA-GSH cycle strength, decreased oxidative stress, and spikelet degeneration rate were closely associated with the synergistically elevated BR and ABA levels in young panicles in MD. In contrast, low BR and excessive ABA levels led to an increase in spikelet degeneration in SD. The three cultivars exhibited the same tendencies. The intrinsic link among AsA-GSH cycle, oxidative stress, spikelet degeneration rate, and BR and ABA levels was further verified by using transgenic rice lines and chemical regulators. BRs or ABA play a unique role in regulating spikelet degeneration. Synergistically increased BR and ABA levels in MD could work together to strengthen AsA-GSH cycle activity, leading to a reduction in oxidative damage and spikelet degeneration. On the other hand, a severe imbalance between low BR and excessive ABA levels may have contributed to the opposite effects in SD.

A transcriptional atlas identifies key regulators and networks for the development of spike tissues in barley.

Grain number and size determine grain yield in crops and are closely associated with spikelet fertility and grain filling in barley (Hordeum vulgare). Abortion of spikelet primordia within individual barley spikes causes a 30%-50% loss in the potential number of grains during development from the awn primordium stage to the tipping stage, after that grain filling is the primary factor regulating grain size. To identify transcriptional signatures associated with spike development, we use a six-rowed barley cultivar (Morex) to develop a spatiotemporal transcriptome atlas containing 255 samples covering 17 stages and 5 positions along the spike. We identify several fundamental regulatory networks, in addition to key regulators of spike development and morphology. Specifically, we show HvGELP96, encoding a GDSL domain-containing protein, as a regulator of spikelet fertility and grain number. Our transcriptional atlas offers a powerful resource to answer fundamental questions in spikelet development and degeneration in barley.

Unraveling the genetic basis of grain number-related traits in a wheat-Agropyron cristatum introgressed line through high-resolution linkage mapping.

BACKGROUND: Grain number per spike (GNS) is a pivotal determinant of grain yield in wheat. Pubing 3228 (PB3228), a wheat-Agropyron cristatum germplasm, exhibits a notably higher GNS. RESULTS: In this study, we developed a recombinant inbred line (RIL) population derived from PB3228/Gao8901 (PG-RIL) and constructed a high-density genetic map comprising 101,136 loci, spanning 4357.3 cM using the Wheat 660 K SNP array. The genetic map demonstrated high collinearity with the wheat assembly IWGSC RefSeq v1.0. Traits related to grain number and spikelet number per spike were evaluated in seven environments for quantitative trait locus (QTL) analysis. Five environmentally stable QTLs were detected in at least three environments. Among these, two major QTLs, QGns-4A.2 and QGns-1A.1, associated with GNS, exhibited positive alleles contributed by PB3228. Further, the conditional QTL analysis revealed a predominant contribution of PB3228 to the GNS QTLs, with both grain number per spikelet (GNSL) and spikelet number per spike (SNS) contributing to the overall GNS trait. Four kompetitive allele-specific PCR (KASP) markers that linked to QGns-4A.2 and QGns-1A.1 were developed and found to be effective in verifying the QTL effect within a diversity panel. Compared to previous studies, QGns-4A.2 exhibited stability across different trials, while QGns-1A.1 represents a novel QTL. The results from unconditional and conditional QTL analyses are valuable for dissecting the genetic contribution of the component traits to GNS at the individual QTL level and for understanding the genetic basis of the superior grain number character in PB3228. The KASP markers can be utilized in marker-assisted selection for enhancing GNS. CONCLUSIONS: Five environmentally stable QTLs related to grain number and spikelet number per spike were identified. PB3228 contributed to the majority of the QTLs associated with GNS.

Evolution of cereal floral architecture and threshability.

Hulled grains, while providing natural protection for seeds, pose a challenge to manual threshing due to the pair of glumes tightly encasing them. Based on natural evolution and artificial domestication, gramineous crops evolved various hull-like floral organs. Recently, progress has been made in uncovering novel domesticated genes associated with cereal threshability and deciphering common regulatory modules pertinent to the specification of hull-like floral organs. Here we review morphological similarities, principal regulators, and common mechanisms implicated in the easy-threshing traits of crops. Understanding the shared and unique features in the developmental process of cereal threshability may not only shed light on the convergent evolution of cereals but also facilitate the de novo domestication of wild cereal germplasm resources through genome-editing technologies.

Endophytic Fungus Reshapes Spikelet Microbiome to Reduce Mycotoxin Produced by Fusarium proliferatum through Altering Rice Metabolites.

Rice spikelet rot disease (RSRD) caused by Fusarium proliferatum seriously reduces rice yield and produces mycotoxins that threaten human health. The root symbiotic endophytic fungus Phomopsis liquidambaris reduces RSRD incidence and fumonisins accumulation in grain by 21.5 and 9.3%, respectively, while the mechanism of disease resistance remains largely elusive. Here, we found that B3 significantly reduced the abundance of pathogen from 79.91 to 2.84% and considerably enriched resistant microbes Pseudomonas and Proteobacteria in the spikelet microbial community. Further study revealed that B3 altered the metabolites of spikelets, especially hordenine and l-aspartic acid, which played a key role in reshaping the microbiome and supporting the growth of the functional core microbe Pseudomonas, and inhibited the pathogen growth and mycotoxin production. This study provided a feasibility of regulating the function of aboveground microbial communities by manipulating plant subsurface tissues to control disease and mycotoxin pollutants in agricultural production.

Development and Characterization of Near-Isogenic Lines Derived from Synthetic Wheat Revealing the 2 kb Insertion in the PPD-D1 Gene Responsible for Heading Delay and Grain Number Improvement.

Spikelet number and grain number per spike are two crucial and correlated traits for grain yield in wheat. Photoperiod-1 (Ppd-1) is a key regulator of inflorescence architecture and spikelet formation in wheat. In this study, near-isogenic lines derived from the cross of a synthetic hexaploid wheat and commercial cultivars generated by double top-cross and two-phase selection were evaluated for the number of days to heading and other agronomic traits. The results showed that heading time segregation was conferred by a single incomplete dominant gene PPD-D1, and the 2 kb insertion in the promoter region was responsible for the delay in heading. Meanwhile, slightly delayed heading plants and later heading plants obviously have advantages in grain number and spikelet number of the main spike compared with early heading plants. Utilization of PPD-D1 photoperiod sensitivity phenotype as a potential means to increase wheat yield potential.

Delayed development of basal spikelets in wheat explains their increased floret abortion and rudimentary nature.

Large differences exist in the number of grains per spikelet across an individual wheat (Triticum aestivum L.) spike. The central spikelets produce the highest number of grains, while apical and basal spikelets are less productive, and the most basal spikelets are commonly only developed in rudimentary form. Basal spikelets are delayed in initiation, yet they continue to develop and produce florets. The precise timing or the cause of their abortion remains largely unknown. Here, we investigated the underlying causes of basal spikelet abortion using shading applications in the field. We found that basal spikelet abortion is likely to be the consequence of complete floret abortion, as both occur concurrently and have the same response to shading treatments. We detected no differences in assimilate availability across the spike. Instead, we show that the reduced developmental age of basal florets pre-anthesis is strongly associated with their increased abortion. Using the developmental age pre-abortion, we were able to predict final grain set per spikelet across the spike, alongside the characteristic gradient in the number of grains from basal to central spikelets. Future efforts to improve spikelet homogeneity across the spike could thus focus on improving basal spikelet establishment and increasing floret development rates pre-abortion.