Panicle Size Research Articles

The plasticity of the oat panicle and associated changes in leaf area and grain weight

The objective of the current investigation was to study the plasticity of the oat panicle together with associated changes in leaf area and grain weight as affected by seed rate and tiller order. Plants (cv. Husky) were sampled from autumn sown seed rate experiments (100, 200, 300, 400, 500 seeds/m2) in 2016 and 2017 after anthesis and separated into their component tillers. The number of primary, secondary and tertiary grains on each whorl of the panicle of each tiller were counted, green leaf area per tiller was measured and, in 2017, the number of green leaves per shoot in addition to leaf length and leaf width were measured. At grain maturity, plants were sampled from three treatments (100, 300, 500 seeds/m2) and separated into their component tillers. The number of primary, secondary and tertiary grains on each whorl were counted and weighed. Primary and secondary grain numbers on all mainstem whorls except the uppermost whorl increased significantly as seed rate decreased, the largest changes being on the bottom whorls. There were also significant increases in green leaf area per stem as seed rate was decreased due to increases both in the number and size of leaves. Grain numbers per whorl decreased significantly with increasing tiller order but green leaf number per stem and leaf area per grain increased with increasing tiller order. The number of secondary grains per panicle was tightly correlated with the number of primary grains per panicle irrespective of seed rate or tiller order. Seed rate had no significant effect on the weight of primary or secondary grains but primary and secondary grain weights were significantly greater on the first tiller compared to the mainstem and second tiller. The oat panicle is a highly plastic organ, the plasticity of the oat panicle contributes to yield stability. Grain weight stability is preserved across a wide range of panicle sizes by changes in leaf area per stem and by the highly stable nature of the relationships between primary and secondary grain numbers and between primary and secondary grain weight.

Strigolactone promotes cytokinin degradation through transcriptional activation of CYTOKININ OXIDASE/DEHYDROGENASE 9 in rice.

Strigolactones (SLs), a group of terpenoid lactones derived from carotenoids, are plant hormones that control numerous aspects of plant development. Although the framework of SL signaling that the repressor DWARF 53 (D53) could be SL-dependently degraded via the SL receptor D14 and F-box protein D3 has been established, the downstream response genes to SLs remain to be elucidated. Here we show that the cytokinin (CK) content is dramatically increased in shoot bases of the rice SL signaling mutant d53 By examining transcript levels of all the CK metabolism-related genes after treatment with SL analog GR24, we identified CYTOKININ OXIDASE/DEHYDROGENASE 9 (OsCKX9) as a primary response gene significantly up-regulated within 1 h of treatment in the wild type but not in d53 We also found that OsCKX9 functions as a cytosolic and nuclear dual-localized CK catabolic enzyme, and that the overexpression of OsCKX9 suppresses the browning of d53 calli. Both the CRISPR/Cas9-generated OsCKX9 mutants and OsCKX9-overexpressing transgenic plants showed significant increases in tiller number and decreases in plant height and panicle size, suggesting that the homeostasis of OsCKX9 plays a critical role in regulating rice shoot architecture. Moreover, we identified the CK-inducible rice type-A response regulator OsRR5 as the secondary SL-responsive gene, whose expression is significantly repressed after 4 h of GR24 treatment in the wild type but not in osckx9 These findings reveal a comprehensive plant hormone cross-talk in which SL can induce the expression of OsCKX9 to down-regulate CK content, which in turn triggers the response of downstream genes.

Sensitivity Analysis of Multifrequency MIMP SAR Data From Rice Paddies

The determination of the accurate composition ratio of scattering mechanisms (volume scattering, double-bounce scattering, and surface scattering) within a radar backscatter is essential to validate current polarimetric decomposition techniques. Multiincidence angle and multipolarimetric synthetic aperture radar (MIMP SAR) observations at the X- and L-bands were applied to rice paddies at late vegetative stage in Niigata City in Japan in 2014 and 2016, respectively. In this paper, multifrequency MIMP SAR analysis is introduced based on the observation results. The approach, combined with theoretical characterization of the data by a discrete scatterer model, showed that rice panicles affect the backscatter from rice paddies. Contrary to expectation, an effect of transmissivity by using different bands is not obvious. The similar level of copolarization (HH and VV) backscatter at X- and L-bands could be explained by the effective size of rice panicles. They are the most characteristic scatters in rice paddy field with respect to multiple frequency polarimetric sensing. In addition, HV shows a distinct sensitivity to the mean orientation angle and the size of panicles regardless of the wavelength. The mean orientation angle affects the polarimetric randomness under azimuthal symmetry, whereas the size of panicles directly affects the attenuation of the volume scattering from the grains. The multifrequency MIMP SAR analysis also indicated the importance of considering the backscatter and attenuation in the interpretation of the backscattering cross section from vegetated fields.

Characterization of Agronomic Traits and Composition of Antioxidant Compounds in Sweet Sorghum (Sorghum bicolor L. Moench) Germplasms

Sweet sorghum (Sorghum bicolor L. Moench) is one of the most important crops for bioethanol production and the provision of antioxidant compounds for human health. In this study, we investigated the 8 agronomic traits of 153 sweet sorghum germplasms, which demonstrated a variety of phenotypes. In particular, nine sweet sorghum germplasms exhibited a sugar content exceeding 20 Brix. Based on agronomic characteristics, we selected eight elite sweet sorghum germplasms that showed highperformance agronomic and growth characteristics such as tall height, large panicle size with short height, high sugar content, and seed-specific characteristics. The selected germplasms also showed significant differential amount of 3 antioxidant compounds of 3-deoxyanthocyanins, flavonoids, and tannins. SS113 contained the highest levels of total 3-deoxyanthocyanins with apigeninidin contents 3-9 fold higher than that of other germplasms, while SS129 had a white seed coat with the highest recorded total flavonoid level (7.52 mg/g) but no detectable 3-deoxyanthocyanins compounds. The characterization of the traits and compounds will be useful for basic research into the selection of suitable cultivars in the breeding of sweet sorghum.

Yield performance of machine-transplanted double-season rice grown following oilseed rape

Growing oilseed rape in the fallow season may be a feasible alternative to growing green manure (e.g. Chinese milk vetch) for improving rice productivity. The objective of this study was to determine the yield performance of machine-transplanted double-season rice (i.e. early- and late-season rice) grown following oilseed rape. Field experiments were conducted to compare machine-transplanted double-season rice grown following oilseed rape, Chinese milk vetch and fallow (i.e. no crop) at Hengyang and Yueyang, Hunan Province, China in three cropping cycles from 2014 to 2017. Results showed that machine-transplanted double-season rice grown following oilseed rape and Chinese milk vetch produced similar grain yield, which was higher than that grown following fallow across two sites and three cropping cycles. The higher grain yield of machine-transplanted double-season rice grown following oilseed rape and Chinese milk vetch was attributable to improvement in both sink size (spikelet number per m2) and source capacity (total biomass). However, the reasons for the improved sink size of machine-transplanted double-season rice grown following oilseed rape and Chinese milk vetch were not entirely the same. Growing oilseed rape increased panicle size (spikelet number per panicle) and panicle number in early- and late-season rice, respectively, while growing Chinese milk vetch increased panicle number in both the early- and late-season rice. Our study suggests that growing oilseed rape in the fallow season is a useful alternative strategy for improving productivity of machine-transplanted double-season rice.

OsMADS18, a membrane-bound MADS-box transcription factor, modulates plant architecture and the abscisic acid response in rice.

The APETALA1 (AP1)/FRUITFULL (FUL)-like transcription factor OsMADS18 plays diverse functions in rice development, but the underlying molecular mechanisms are far from fully understood. Here, we report that down-regulation of OsMADS18 expression in RNAi lines caused a delay in seed germination and young seedling growth, whereas the overexpression of OsMADS18 produced plants with fewer tillers. In targeted OsMADS18 genome-edited mutants (osmads18-cas9), an increased number of tillers, altered panicle size, and reduced seed setting were observed. The EYFP-OsMADS18 (full-length) protein was localized to the nucleus and plasma membrane but the EYFP-OsMADS18-N (N-terminus) protein mainly localized to the nucleus. The expression of OsMADS18 could be stimulated by abscisic acid (ABA), and ABA stimulation triggered the cleavage of HA-OsMADS18 and the translocation of OsMADS18 from the plasma membrane to the nucleus. The inhibitory effect of ABA on seedling growth was less effective in the OsMADS18-overexpressing plants. The expression of a set of ABA-responsive genes was significantly reduced in the overexpressing plants. The phenotypes of transgenic plants expressing EYFP-OsMADS18-N resembled those observed in the osmads18-cas9 mutants. Analysis of the interaction of OsMADS18 with OsMADS14, OsMADS15, and OsMADS57 strongly suggests an essential role for OsMADS18 in rice development.

OsSHI1 Regulates Plant Architecture Through Modulating the Transcriptional Activity of IPA1 in Rice.

Tillering and panicle branching are important determinants of plant architecture and yield potential in rice (Oryza sativa). IDEAL PLANT ARCHITECTURE1 (IPA1) encodesSQUAMOSA PROMOTER BINDING PROTEIN-LIKE14, which acts as a key transcription factor regulating tiller outgrowth and panicle branching by directly activating the expression of O. sativa TEOSINTE BRANCHED1 (OsTB1) and O. sativa DENSE AND ERECT PANICLE1 (OsDEP1), thereby influencing grain yield in rice. Here, we report the identification of a rice mutant named shi1 that is characterized by dramatically reduced tiller number, enhanced culm strength, and increased panicle branch number. Map-based cloning revealed that O. sativa SHORT INTERNODES1 (OsSHI1) encodes a plant-specific transcription factor of the SHI family with a characteristic family-specific IGGH domain and a conserved zinc-finger DNA binding domain. Consistent with the mutant phenotype, OsSHI1 is predominantly expressed in axillary buds and young panicle, and its encoded protein is exclusively targeted to the nucleus. We show that OsSHI1 physically interacts with IPA1 both in vitro and in vivo. Moreover, OsSHI1 could bind directly to the promoter regions of both OsTB1 and OsDEP1 through a previously unrecognized cis-element (T/GCTCTAC motif). OsSHI1 repressed the transcriptional activation activity of IPA1 by affecting its DNA binding activity toward the promoters of both OsTB1 and OsDEP1, resulting in increased tiller number and diminished panicle size. Taken together, our results demonstrate that OsSHI1 regulates plant architecture through modulating the transcriptional activity of IPA1 and provide insight into the establishment of plant architecture in rice.

Continuous applications of biochar to rice: Effects on grain yield and yield attributes

Biochar is considered as a beneficial soil amendment for crop production. However, limited information is available on the effects of continuous applications of biochar on rice. In this study, a fixed field experiment was conducted in the early and late rice-growing seasons from 2015 to 2017. Grain yield and yield attributes with a widely-grown rice cultivar Zhongzao 39 were compared, with and without applications of biochar in each season. The results showed that grain yield initially decreased with biochar applications in the first three seasons due to decreases in grain weight and harvest index. Although there were further relative decreases in grain weight and harvest index for rice that was supplied with biochar in the fourth to sixth seasons, grain yield was increased (by 4–10%) because of increases in sink size (spikelets per m2) and total biomass. The increased sink size in rice whose soil had been supplied with biochar in the fourth to sixth seasons was achieved by increasing panicle size (spikelets per panicle) or number of panicles, or both. Our study suggests that the positive effects of biochar application on rice yield and yield attributes depend on the duration of biochar application. Further investigations are needed to determine what are the soil and physiological processes for producing yield responses associated with ongoing applications of biochar. Also, it should be evaluated the performance of biochar application combined with other management practices, especially those can increase the grain weight and harvest index in rice production.

Long‐Term Selection in Hybrid Sorghum Breeding Programs

Estimating genetic gains in sorghum [Sorghum bicolor (L.) Moench] is necessary to assess whether the current rates of improvement will meet future production demands. The current study was conducted to determine the rate of genetic gain in yield and associated traits over the commercial hybrid era using sorghum germplasm from the Texas A&M sorghum breeding program and a US sorghum seed company. From the Texas A&M AgriLife program, 60 hybrids that represented a 50‐yr span of hybrid breeding were grown and evaluated in five environments across Texas in 2016. In a separate set of trials, 14 commercial hybrids representing a similar timespan were evaluated in three Texas environments in 2016. In both programs, grain sorghum yields increased 0.008 t ha−1 annually over their respective timespans. Traits that increased over time included yield potential per plant, heterosis, test weight, panicle size, and grain number per panicle, whereas leaf angle, days to maturity, plant height, and yield stability demonstrated little to no change. Overall, ∼60% of total yield gains in US sorghum production are attributed to genetic improvement through sorghum breeding. Compared with other major US field crops, the rate of genetic gain in sorghum has been slower, presumably due to a combination of factors, which include continually shifting production environments, changing priorities in traits, reduced research investments (compared with other crops), and less‐than‐optimized heterotic groups.

Effects of short-term heat stress at booting stage on rice-grain quality

Extreme heat-stress events are becoming more frequent under anticipated global warming, which is having devastating effect on grain yield, as well as quality, of rice (Oryza sativa L.). The effects of heat stress at booting stage on grain quality of two japonica varieties, Nanjing41 and Wuyunjing24, were investigated in phytotrons during 2014 and 2015. Rice plants were subjected to four mean temperature regimes 27°C, 31°C, 35°C and 39°C of 2, 4 and 6 days’ duration. The results showed that high temperatures of 35°C and 39°C for 4 and 6 days significantly reduced panicle size, seed-setting rate, grain size, chalky grain rate, milling characteristics and amylose content, but increased protein content. Severe heat stress decreased values of peak viscosity and breakdown, and increased pasting temperature. An increase in heat degree-days decreased the percentage of chalky grains exponentially, and decreased amylose content and increased protein content linearly. Sensitivity of grain quality to heat stress in the two varieties differed among quality traits and with heat stress intensity. This study indicates that rice-grain quality had some resistance to mild heat stress, but it could not withstand severe heat stress at booting. Short-term heat stress at booting stage deteriorates most grain-quality traits, posing a potential risk to rice quality. The impacts on grain quality could be well quantified by the combined effects of the intensity and duration of heat stress at booting stage.

Improved Upland Rice: Adaptability, Agronomic and Farmer Acceptability Assessment under Semi-Arid Conditions of South Western Uganda

Enhancing the ability of plants to tolerate abiotic and biotic stresses is the cur-rent strategy for increasing agricultural productivity worldwide. Improved up-land rice varieties characterized by early maturity, high disease resistance, high drought tolerance, high yielding potential, high grain quality and marketability are required by farmers to increase upland rice production to meet the increas-ing food and income demands. Improved and local upland rice varieties were evaluated across two seasons with and without fertilizer application. Insuffi-cient soil water availability, low soil fertility and the blast disease were the major stresses that affected upland rice in the Rubirizi and Mitooma experi-mental sites in the South Western Agro Ecological Zone of Uganda. Integration of improved rice variety and soil fertility amendment with fertilizer plus proper crop management cultural practices resulted in high agronomic performance. Varieties NamChe 4, NamChe 5 and E22 showed superior performance over the other varieties in the field, and had significantly high probability (P ≤ 0.15) of being accepted by farmers. The early maturing NERICA 10, late maturing NERICA 6, SUPERICA 1 and Local Var., had high probabilities of being re-jected because of low yielding, late maturity, drought intolerance, small panicle size, poor grain filling and high susceptibility to rice blast caused by Mag-naporthe grisea. Therefore, improved varieties have great potential of increas-ing rice production in SWAEZ-Uganda, if farmers adopt the multi-technology integration approach.

Field‐based robotic phenotyping of sorghum plant architecture using stereo vision

AbstractSorghum (Sorghum bicolor) is known as a major feedstock for biofuel production. To improve its biomass yield through genetic research, manually measuring yield component traits (e.g. plant height, stem diameter, leaf angle, leaf area, leaf number, and panicle size) in the field is the current best practice. However, such laborious and time‐consuming tasks have become a bottleneck limiting experiment scale and data acquisition frequency. This paper presents a high‐throughput field‐based robotic phenotyping system which performed side‐view stereo imaging for dense sorghum plants with a wide range of plant heights throughout the growing season. Our study demonstrated the suitability of stereo vision for field‐based three‐dimensional plant phenotyping when recent advances in stereo matching algorithms were incorporated. A robust data processing pipeline was developed to quantify the variations or morphological traits in plant architecture, which included plot‐based plant height, plot‐based plant width, convex hull volume, plant surface area, and stem diameter (semiautomated). These image‐derived measurements were highly repeatable and showed high correlations with the in‐field manual measurements. Meanwhile, manually collecting the same traits required a large amount of manpower and time compared to the robotic system. The results demonstrated that the proposed system could be a promising tool for large‐scale field‐based high‐throughput plant phenotyping of bioenergy crops.

Down regulation of a heavy metal transporter gene influences several domestication traits and grain Fe-Zn content in rice

Biofortification of rice (Oryza sativa L.) would alleviate iron and zinc deficiencies in the target populations. We identified two alleles 261 and 284 of a Gramineae-specific heavy metal transporter gene OsHMA7 by analyzing expression patterns and sequences of genes within QTLs for high Fe & Zn, in Madhukar x Swarna recombinant inbred lines (RILs) with high (HL) or low (LL) grain Fe & Zn. Overexpression of 261 allele increased grain Fe and Zn but most of the transgenic plants either did not survive or did not yield enough seeds and could not be further characterized. Knocking down expression of OsHMA7 by RNAi silencing of endogenous gene resulted in plants with altered domestication traits such as plant height, tiller number, panicle size and architecture, grain color, shape, size, grain shattering, heading date and increased sensitivity to Fe and Zn deficiency. However, overexpression of 284 allele resulted in transgenic lines with either high grain Fe & Zn content (HL-ox) and tolerance to Fe and Zn deficiency or low grain Fe & Zn content (LL-ox) and phenotype similar to RNAi-lines. OsHMA7 transcript levels were five-fold higher in the HL-ox plants whereas LL-ox and RNAi plants showed 2–3 fold reduced levels compared to Kitaake control. Spraying LL-ox and RNAi lines with Fe & Zn at grain filling stage resulted in increased grain yield, significant increase in Fe & Zn content and brown pericarp. Altered expression of OsHMA7 influenced transcript levels of iron-responsive genes indicating cellular Fe-Zn homeostasis and also several domestication-related genes in rice. Our study shows that a novel heavy metal transporter gene influences yield and grain Fe & Zn content and has potential to improve rice production and biofortification.

Why high grain yield can be achieved in single seedling machine-transplanted hybrid rice under dense planting conditions?

This study was conducted to identify the factors associated with high grain yield in single seedling machine-transplanted hybrid rice under dense planting conditions. Field experiments were done in Yong'an Town, Hunan Province, China in 2015 and 2016. Two hybrid rice cultivars were grown under single seedling machine transplanting (SMT) and conventional machine transplanting (CMT) at a high planting density in each year. Grain yield and yield attributes were compared between SMT and CMT. Averaged across cultivars and years, grain yield was 12% higher under SMT than under CMT. Plant height, basal stem width, and shoot and root dry weights were higher in seedlings for SMT than those for CMT. SMT had less maximum tiller number per m2 and consequently less panicle number per m2 than did CMT. Branch number per panicle, especially the secondary branch number per panicle, and spikelet number per cm of panicle length were more under SMT than under CMT, which resulted in more spikelet number per panicle under SMT than under CMT. SMT had higher or equal spikelet filling percentage than did CMT. The difference in grain weight between SMT and CMT was relatively small and inconsistent cross years. SMT had higher or equal total biomass and harvest index than did CMT. Dry weight per stem under SMT was heavier than that under CMT. Larger leaf area per stem was partly responsible for the heavier dry weight per stem under SMT than under CMT. Our study suggests that improvement in seedling quality, panicle size, and dry weight per stem are critical to the high grain yield in single seedling machine-transplanted hybrid rice under dense planting conditions.

Site-specific nutrient management enhances sink size, a major yield constraint in rainfed lowland rice

Nutrient management can increase crop yield and income, but its effects on yield components are rarely dissected in on-farm research. In this study, we compared aboveground biomass and yield components of rainfed lowland rice under site-specific nutrient management and farmer management from 69 demonstration sites prone to mild to moderate intermittent drought across 9 Philippine provinces over 3 years (the 2011–2013 wet seasons). The sink size (spikelets m−2) was most closely associated with grain yield in all years. Panicle size (spikelets per panicle) increased by 10.4% and 13.0% in 2011 and 2012, respectively, under site-specific nutrient management, with N application around the early reproductive stage of <25 kg N ha−1 in farmer nutrient management versus 30–33 kg N ha−1 in site-specific management. Higher N application during seedling establishment in farmer nutrient management (55 kg N ha−1) than in site-specific management (22 kg N ha−1) did not increase panicles m−2 in any year. Our results demonstrate the yield advantage of site-specific nutrient management in rainfed lowland rice in relatively fertile and less drought-prone environments: enhancing sink size should be the major target of nutrient management; it is unnecessary to apply high amounts of N during seedling establishment to secure a sufficient panicle number; and N application is most important during the early reproductive stage to increase panicle size.

Integrating mechanization with agronomy and breeding to ensure food security in China

Productivity of intensive rice cropping systems plays a pivotal role in national food security in China. By 2030, a 20% increase in rice yield will be required to meet the growing demand for food that will result from population growth. The success of China’s super hybrid rice was expected to provide an opportunity to cope with the increased demand for rice. However, in China the planting area of super hybrid rice is less than 8% of the national total rice planting area and the planting area of hybrid rice has continued to decline since 1996. The decreased planting area of hybrid rice is related to the shift in rice establishment methods from manual transplanting to direct seeding and mechanical transplanting. These shifts can result in increased seeding rates and reduced morphological advantages of heterosis (e.g. reduced panicle size), both of which can influence cultivar choice by rice farmers, who will tend to favor cheaper inbred cultivars. The shifts in rice establishment methods can also eliminate or reduce the seedling nursey period and subsequently shorten the growth duration and negatively affect the yield. We anticipate that the above problems will be resolved by integrating mechanization (e.g. designing high-precision seed sowing machines) with agronomy (e.g. improving management practices for increasing seed vigor) and breeding (e.g. developing high-yielding cultivars with short growth durations). This strategy also has implications for production of other crops in intensive farming systems in China and for other developing countries with rice-based intensive cropping systems.

Phylogenetic and CRISPR/Cas9 Studies in Deciphering the Evolutionary Trajectory and Phenotypic Impacts of Rice ERECTA Genes.

The ERECTA family genes (ERfs) have been found to play diverse functions in Arabidopsis, including controlling cell proliferation and cell growth, regulating stomata patterning, and responding to various stresses. This wide range of functions has rendered them as a potential candidate for crop improvement. However, information on their functional roles, particularly their morphological impact, in crop genomes, such as rice, is limited. Here, through evolutionary prediction, we first depict the evolutionary trajectory of the ER family, and show that the ER family is actually highly conserved across different species, suggesting that most of their functions may also be observed in other plant species. We then take advantage of the CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats–associated nuclease 9) system to assess their morphological impact on one of the most important crops, rice. Loss-of-function mutants of OsER1 and OsER2 display shortened plant stature and reduced panicle size, suggesting they possibly also functioned in regulating cell proliferation and cell growth in rice. In addition to functions similar to that in Arabidopsis, we also find clues that rice ERfs may play unique functional roles. The OsER2 displayed more severe phenotypic changes than OsER1, indicating putative differentiation in their functions. The OsERL might be of essential in its function, and the proper function of all three rice ER genes might be dependent of their genetic background. Future investigations relating to these functions are key to exploiting ERfs in crop development.

OsALMT7 Maintains Panicle Size and Grain Yield in Rice by Mediating Malate Transport.

Panicle size is a critical determinant of grain yield in rice (Oryza sativa) and other grain crops. During rice growth and development, spikelet abortion often occurs at either the top or the basal part of the panicle under unfavorable conditions, causing a reduction in fertile spikelet number and thus grain yield. In this study, we report the isolation and functional characterization of a panicle abortion mutant named panicle apical abortion1-1 (paab1-1). paab1-1 exhibits degeneration of spikelets on the apical portion of panicles during late stage of panicle development. Cellular and physiological analyses revealed that the apical spikelets in the paab1-1 mutant undergo programmed cell death, accompanied by nuclear DNA fragmentation and accumulation of higher levels of H2O2 and malondialdehyde. Molecular cloning revealed that paab1-1 harbors a mutation in OsALMT7, which encodes a putative aluminum-activated malate transporter (OsALMT7) localized to the plasma membrane, and is preferentially expressed in the vascular tissues of developing panicles. Consistent with a function for OsALMT7 as a malate transporter, the panicle of the paab1-1 mutant contained less malate than the wild type, particularly at the apical portions, and injection of malate into the paab1-1 panicle could alleviate the spikelet degeneration phenotype. Together, these results suggest that OsALMT7-mediated transport of malate into the apical portion of panicle is required for normal panicle development, thus highlighting a key role of malate in maintaining the sink size and grain yield in rice and probably other grain crops.

GRAIN SIZE AND NUMBER1 Negatively Regulates the OsMKKK10-OsMKK4-OsMPK6 Cascade to Coordinate the Trade-off between Grain Number per Panicle and Grain Size in Rice.

Grain number and size are interactive agronomic traits that determine grain yield. However, the molecular mechanisms responsible for coordinating the trade-off between these traits remain elusive. Here, we characterized the rice (Oryza sativa) grain size and number1 (gsn1) mutant, which has larger grains but sparser panicles than the wild type due to disordered localized cell differentiation and proliferation. GSN1 encodes the mitogen-activated protein kinase phosphatase OsMKP1, a dual-specificity phosphatase of unknown function. Reduced expression of GSN1 resulted in larger and fewer grains, whereas increased expression resulted in more grains but reduced grain size. GSN1 directly interacts with and inactivates the mitogen-activated protein kinase OsMPK6 via dephosphorylation. Consistent with this finding, the suppression of mitogen-activated protein kinase genes OsMPK6, OsMKK4, and OsMKKK10 separately resulted in denser panicles and smaller grains, which rescued the mutant gsn1 phenotypes. Therefore, OsMKKK10-OsMKK4-OsMPK6 participates in panicle morphogenesis and acts on a common pathway in rice. We confirmed that GSN1 is a negative regulator of the OsMKKK10-OsMKK4-OsMPK6 cascade that determines panicle architecture. The GSN1-MAPK module coordinates the trade-off between grain number and grain size by integrating localized cell differentiation and proliferation. These findings provide important insights into the developmental plasticity of the panicle and a potential means to improve crop yields.

MSD1 regulates pedicellate spikelet fertility in sorghum through the jasmonic acid pathway

Grain number per panicle (GNP) is a major determinant of grain yield in cereals. However, the mechanisms that regulate GNP remain unclear. To address this issue, we isolate a series of sorghum [Sorghum bicolor (L.) Moench] multiseeded (msd) mutants that can double GNP by increasing panicle size and altering floral development so that all spikelets are fertile and set grain. Through bulk segregant analysis by next-generation sequencing, we identify MSD1 as a TCP (Teosinte branched/Cycloidea/PCF) transcription factor. Whole-genome expression profiling reveals that jasmonic acid (JA) biosynthetic enzymes are transiently activated in pedicellate spikelets. Young msd1 panicles have 50% less JA than wild-type (WT) panicles, and application of exogenous JA can rescue the msd1 phenotype. Our results reveal a new mechanism for increasing GNP, with the potential to boost grain yield, and provide insight into the regulation of plant inflorescence architecture and development.