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.

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.

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.

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.

Cold-upregulated glycosyltransferase gene 1 (OsCUGT1) plays important roles in rice height and spikelet fertility.

Glycosyltransferases (GTs) regulate many physiological processes and stress responses in plants. However, little is known about the function of GT in rice development. In this study, molecular analyses revealed that the expression of a rice GT gene (Cold-Upregulated Glycosyltransferase Gene 1, CUGT1) is developmentally controlled and stress-induced. OsCUGT1 was knocked out by using the clustered regularly interspaced short palindromic repeats (CRISPR) system to obtain the mutant oscugt1, which showed a severe dwarf and sterility phenotype. Further cytological analyses indicated that the dwarfism seen in the oscugt1 mutant might be caused by fewer and smaller cells. Histological pollen analysis suggests that the spikelet sterility in oscugt1 mutants may be caused by abnormal microsporogenesis. Moreover, multiple transgenic plants with knockdown of OsCUGT1 expression through RNA interference were obtained, which also showed obvious defects in plant height and fertility. RNA sequencing revealed that multiple biological processes associated with phenylpropanoid biosynthesis, cytokinin metabolism and pollen development are affected in the oscugt1 mutant. Overall, these results suggest that rice OsCUGT1 plays an essential role in rice development.

Quantitative trait loci (QTL) for low temperature tolerance at the young microspore stage in rice (Oryza sativa L.) in Australian breeding material.

Low temperatures at the young microspore stage (YMS) decreases spikelet fertility and is a major limiting factor to rice production in temperate Australia. Low temperature tolerance is a difficult trait to phenotype, hence there is a strong desire for the identification of quantitative trait loci (QTL) for their use in marker-assisted selection (MAS). Association mapping was used in several breeding populations with a known source of low temperature tolerance, Norin PL8, to identify QTL for low temperature tolerance. A novel QTL for spikelet fertility was identified on chromosome 6, qYMCT6.1, in which the Australian variety, Kyeema, was the donor for increased fertility. Additional five genomics regions were identified that co-located with previously reported QTL, two of which have been previously cloned. Additionally, for the first time a QTL for spikelet fertility qYMCT10.1, has been shown to co-locate with the number of dehisced anthers qYMCTF10.1 which increases the shedding of pollen from the anthers. This study revealed one new QTL for low temperature tolerance at YMS in temperate japonica germplasm and identified an additional five previously reported. These QTL will be utilised for MAS in the Australian rice breeding program and may have merit for temperate breeding programs globally.

Screening and identification of genes affecting grain quality and spikelet fertility during high-temperature treatment in grain filling stage of rice.

BACKGROUND: Recent temperature increases due to rapid climate change have negatively affected rice yield and grain quality. Particularly, high temperatures during right after the flowering stage reduce spikelet fertility, while interfering with sugar energy transport, and cause severe damage to grain quality by forming chalkiness grains. The effect of high-temperature on spikelet fertility and grain quality during grain filling stage was evaluated using a double haploid line derived from another culture of F1 by crossing Cheongcheong and Nagdong cultivars. Quantitative trait locus (QTL) mapping identifies candidate genes significantly associated with spikelet fertility and grain quality at high temperatures. RESULTS: Our analysis screened OsSFq3 that contributes to spikelet fertility and grain quality at high-temperature. OsSFq3 was fine-mapped in the region RM15749-RM15689 on chromosome 3, wherein four candidate genes related to the synthesis and decomposition of amylose, a starch component, were predicted. Four major candidate genes, including OsSFq3, and 10 different genes involved in the synthesis and decomposition of amylose and amylopectin, which are starch constituents, together with relative expression levels were analyzed. OsSFq3 was highly expressed during the initial stage of high-temperature treatment. It exhibited high homology with FLOURY ENDOSPERM 6 in Gramineae plants and is therefore expected to function similarly. CONCLUSION: The QTL, major candidate genes, and OsSFq3 identified herein could be effectively used in breeding rice varieties to improve grain quality, while tolerating high temperatures, to cope with climate changes. Furthermore, linked markers can aid in marker-assisted selection of high-quality and -yield rice varieties tolerant to high temperatures.

Silicon application improves caryopsis development and yield in rice.

BACKGROUND: Caryopsis development consists of several processes in the production of grain yield in field crops. This study evaluated the effect of silicon (Si) on spikelet formation, spikelet fertility, and grain filling and its impact on grain yield in rice. RESULTS: Applying Si increased grain yield by 44% in Chainat 1( CNT1) and by 23% in Pathumthani 1 (PTT1). With no Si application, CNT1 had fewer total spikelets, and the fertilized and filled spikelets responded more strongly to Si than PTT1 did. Grain yield in both genotypes increased with increasing number of spikelets and filled fertilized grains. There were close relationships between Si concentration in the shoots, flag leaf, and the husk, which were positively correlated with grain yield, the number of spikelets, and fertilized and filled grains. Applying Si fertilizer also increased the expression level of Lsi6 in both CNT1 and PTT1 by 202% and 144% respectively compared with the expression of plants with no Si supplied. CONCLUSION: This study has shown how rice grain yield can be limited by Si deficiency through the spikelet formation, fertilization, and grain filling processes. Applying Si fertilizer could improve rice grain yield through increasing spikelet formation, fertilization, and grain filling, which is in parallel with Lsi6 gene expression. This information can be used for improving rice productivity by Si fertilization management. © 2020 Society of Chemical Industry.

Acid invertase confers heat tolerance in rice plants by maintaining energy homoeostasis of spikelets.

Heat stress impairs both pollen germination and pollen tube elongation, resulting in pollination failure caused by energy imbalance. Invertase plays a critical role in the maintenance of energy homoeostasis; however, few studies investigated this during heat stress. Two rice cultivars with different heat tolerance, namely, TLY83 (heat tolerant) and LLY722 (heat susceptible), were subjected to heat stress. At anthesis, heat stress significantly decreased spikelet fertility, accompanied by notable reductions in pollen germination on stigma and pollen tube elongation in ovule, especially in LLY722. Acid invertase (INV), rather than sucrose synthase, contributed to sucrose metabolism, which explains the different tolerances of both cultivars. Under heat stress, larger enhancements in NAD(H), ATP, and antioxidant capacity were found in TLY83 compared with LLY722, whereas a sharp reduction in poly(ADP-ribose) polymerase (PARP) activity was found in the former compared with the latter. Importantly, exogenous INV, 3-aminobenzamide (a PARP inhibitor), sucrose, glucose, and fructose significantly increased spikelet fertility under heat stress, where INV activity was enhanced and PARP activity was inhibited. Therefore, INV can balance the energy production and consumption to provide sufficient energy for pollen germination and pollen tube growth under heat stress.

Deterioration of ovary plays a key role in heat stress-induced spikelet sterility in sorghum.

In sorghum (Sorghum bicolor [L.] Moench), the impact of heat stress during flowering on seed set is known, but mechanisms that lead to tolerance are not known. A diverse set of sorghum genotypes was tested under controlled environment and field conditions to ascertain the impact of heat stress on time-of-day of flowering, pollen viability, and ovarian tissue. A highly conserved early morning flowering was observed, wherein >90% of spikelets completed flowering within 30 min after dawn, both in inbreds and hybrids. A strong quantitative impact of heat stress was recorded before pollination (reduced pollen viability) and post pollination (reduced pollen tube growth and linear decline in fertility). Although viable pollen tube did reach the micropylar region, 100% spikelet sterility was recorded under 40/22°C (day/night temperatures), even in the tolerant genotype Macia. Heat stress induced significant damage to the ovarian tissue near the micropylar region, leading to highly condensed cytoplasmic contents and disintegrated nucleolus and nucleus in the susceptible genotype RTx430. Whereas, relatively less damages to ovarian cell organelles were observed in the tolerant genotype Macia under heat stress. Integrating higher tolerance in female reproductive organ will help in effective utilization of the early morning flowering mechanism to enhance sorghum productivity under current and future hotter climate.

Interaction between row-type genes in barley controls meristem determinacy and reveals novel routes to improved grain.

Hordeum species develop a central spikelet flanked by two lateral spikelets at each inflorescence node. In 'two-rowed' spikes, the central spikelet alone is fertile and sets grain, while in 'six-rowed' spikes, lateral spikelets can also produce grain. Induced loss-of-function alleles of any of five Six-rowed spike (VRS) genes (VRS1-5) cause complete to intermediate gains of lateral spikelet fertility. Current six-row cultivars contain natural defective vrs1 and vrs5 alleles. Little information is known about VRS mechanism(s). We used comparative developmental, expression and genetic analyses on single and double vrs mutants to learn more about how VRS genes control development and assess their agronomic potential. We show that all VRS genes repress fertility at carpel and awn emergence in developing lateral spikelets. VRS4, VRS3 and VRS5 work through VRS1 to suppress fertility, probably by inducing VRS1 expression. Pairing vrs3, vrs4 or vrs5 alleles increased lateral spikelet fertility, despite the presence of a functional VRS1 allele. The vrs3 allele caused loss of spikelet identity and determinacy, improved grain homogeneity and increased tillering in a vrs4 background, while with vrs5, decreased tiller number and increased grain weight. Interactions amongst VRS genes control spikelet infertility, determinacy and outgrowth, and novel routes to improving six-row grain.

Boron application improves yield of rice cultivars under high temperature stress during vegetative and reproductive stages.

It is reported that high temperatures (HT) would cause a marked decrease in world rice production. In tropical regions, high temperatures are a constraint to rice production and the most damaging effect is on spikelet sterility. Boron (B) plays a very important role in the cell wall formation, sugar translocation, and reproduction of the rice crop and could play an important role in alleviating high temperature stress. A pot culture experiment was conducted to study the effect of B application on high temperature tolerance of rice cultivars in B-deficient soil. The treatments comprised of four boron application treatments viz. control (B0), soil application of 1 kg B ha-1 (B1), soil application of 2 kg B ha-1 (B2), and foliar spray of 0.2% B (Bfs); three rice cultivars viz. Annapurna (HT stress tolerant), Naveen, and Shatabdi (both HT stress susceptible); and three temperature regimes viz. ambient (AT), HT at vegetative stage (HTV), and HT at reproductive stage (HTR). The results revealed that high temperature stress during vegetative or flowering stage reduced grain yield of rice cultivars mainly because of low pollen viability and spikelet fertility. The effects of high temperature on the spikelet fertility and grain filling varied among cultivars and the growth stages of plant when exposed to the high temperature stress. Under high temperature stress, the tolerant cultivar displays higher cell membrane stability, less accumulation of osmolytes, more antioxidant enzyme activities, and higher pollen viability and spikelet fertility than the susceptible cultivars. In the present work, soil application of boron was effective in reducing the negative effects of high temperature both at vegetative and reproductive stages. Application of B results into higher grain yield under both ambient and high temperature condition over control for all the three cultivars; however, more increase was observed for the susceptible cultivar over the tolerant one. The results suggest that the exogenous application of boron had a substantial effect on cell membrane stability, sugar mobilization, pollen viability, and spikelet fertility, hence the yield. The cultivars due to their variation in the tolerance level for high temperature stress behaved differently, and at high temperature stress, more response of the application of boron was seen in susceptible cultivars.

iTRAQ-Based Quantitative Proteomics Analysis on Rice Anther Responding to High Temperature.

As one of the most important crops, rice provides the major food for more than half of the world population. However, its production is limited by many environmental factors, among which high temperature stress (HS) frequently occurs during anthesis and reduces its spikelet fertility. To explore the mechanism of HS tolerance in rice, we conducted a comparative proteomics analysis on the anthers between HS resistant and sensitive cultivars under different levels of high temperature. Under the same HS treatment, the resistant cultivar showed much higher spikelet fertility than the sensitive cultivar. Proteomic data showed that HS lead to the degradation of ribosomal proteins in the sensitive cultivar but not in the resistant one, which might result in the injury of protein biosynthetic machinery. In contrast, HS induced the increase of sHSP, ß-expansins and lipid transfer proteins in the resistant cultivar, which might contribute to its ability to tolerate HS. The results provide some new insights into the mechanism of rice HS response.

Unraveling the molecular basis of oxidative stress management in a drought tolerant rice genotype Nagina 22.

BACKGROUND: Drought stress tolerance for crop improvement is an important goal worldwide. Drought is a complex trait, and it is vital to understand the complex physiological, biochemical, and molecular mechanisms of drought tolerance to tackle it effectively. Osmotic adjustment, oxidative stress management (OSM), and cell membrane stability (CMS) are major components of cellular tolerance under drought stress. In the current study, we explored the molecular basis of OSM in the drought tolerant rice variety, Nagina 22 and compared it with the popular drought sensitive rice variety, IR 64, under drought imposed at the reproductive stage, to understand how the parental polymorphisms correlate with the superiority of Nagina 22 and tolerant bulk populations under drought. RESULTS: We generated recombinant inbred lines (RIL) from contrasting parents Nagina 22 and IR 64 and focussed on spikelet fertility (SF), in terms of its correlation with OSM, which is an important component of drought tolerance in Nagina 22. Based on SF under drought stress and its correlations with other yield related traits, we used superoxide dismutase (SOD), glutathione reductase (GR), and ascorbate peroxidase (APX) activity assays to establish the relationship between SF and OSM genes in the tolerant and sensitive lines. Among the OSM enzymes studied, GR had a significant and positive correlation with single plant yield (SPY) under drought stress. GR was also positively correlated with APX but negatively so with SOD. Interestingly, none of the enzyme-morphology correlations were significant under irrigated control (IC). Through genome-wide SNP analysis of the 21 genes encoding for OSM enzymes, we identified the functional polymorphisms between the parents and identified superior alleles. By using network analysis of OSM genes in rice, we identified the genes that are central to the OSM network. CONCLUSIONS: From the biochemical and morphological data and the SNP analysis, the superiority of Nagina 22 in spikelet fertility under drought stress is because of its superior alleles for SOD (SOD2, SODCC1, SODA) and GR (GRCP2) rather than for APX, for which IR 64 had the superior allele (APX8). Nagina 22 can bypass APX8 by directly interacting with SODA. For nine of the 11 genes present in the central network, Nagina 22 had the superior alleles. We propose that Nagina 22 tolerance could mainly be because of SODA which is a reactive oxygen scavenger in mitochondria which is directly associated with spikelet fertility.

Genome-Wide Transcriptome Analysis During Anthesis Reveals New Insights into the Molecular Basis of Heat Stress Responses in Tolerant and Sensitive Rice Varieties.

Rice is one of the main food crops in the world. In the near future, yield is expected to be under pressure due to unfavorable climatic conditions, such as increasing temperatures. Therefore, improving rice germplasm in order to guarantee rice production under harsh environmental conditions is of top priority. Although many physiological studies have contributed to understanding heat responses during anthesis, the most heat-sensitive stage, molecular data are still largely lacking. In this study, an RNA-sequencing approach of heat- and control-treated reproductive tissues during anthesis was carried out using N22, one of the most heat-tolerant rice cultivars known to date. This analysis revealed that expression of genes encoding a number of transcription factor families, together with signal transduction and metabolic pathway genes, is repressed. On the other hand, expression of genes encoding heat shock factors and heat shock proteins was highly activated. Many of these genes are predominantly expressed at late stages of anther development. Further physiological experiments using heat-tolerant N22 and two sensitive cultivars suggest that reduced yield in heat-sensitive plants may be associated with poor pollen development or production in anthers prior to anthesis. In parallel, induction levels of a set of heat-responsive genes in these tissues correlated well with heat tolerance. Altogether, these findings suggest that proper expression of protective chaperones in anthers is needed before anthesis to overcome stress damage and to ensure fertilization. Genes putatively controlling this process were identified and are valuable candidates to consider for molecular breeding of highly productive heat-tolerant cultivars.

Gibberellic Acid: A Key Phytohormone for Spikelet Fertility in Rice Grain Production.

The phytohormone gibberellic acid (GA) has essential signaling functions in multiple processes during plant development. In the "Green Revolution", breeders developed high-yield rice cultivars that exhibited both semi-dwarfism and altered GA responses, thus improving grain production. Most studies of GA have concentrated on germination and cell elongation, but GA also has a pivotal role in floral organ development, particularly in stamen/anther formation. In rice, GA signaling plays an important role in spikelet fertility; however, the molecular genetic and biochemical mechanisms of GA in male fertility remain largely unknown. Here, we review recent progress in understanding the network of GA signaling and its connection with spikelet fertility, which is tightly associated with grain productivity in cereal crops.

Field level evaluation of rice introgression lines for heat tolerance and validation of markers linked to spikelet fertility.

Rice lines derived from wild species and mutants can serve as a good resource for favorable alleles for heat tolerance. In all, 48 stable lines including 17 KMR3/O. rufipogon introgression lines (KMR3 ILs), 15 Swarna/O. nivara ILs (Swarna ILs) along with their parents, Nagina 22 (N22) and its 4 EMS induced mutants and 7 varieties were evaluated for heat tolerance under irrigated conditions under field in two seasons, wet season 2012 using poly cover house method and dry season 2013 using late sown method. Spikelet fertility (SF), yield per plant (YP) and heat susceptibility index (HSI) for these two traits were considered as criteria to assess heat tolerance compared to control. Four KMR3 ILs and eight Swarna ILs were identified as heat tolerant based on SF and YP and their HSIs in both wet and dry seasons. S-65 and S-70 showed low SF and high YP consistently in response to heat in both seasons. We provide evidence that SF alone may not be the best criterion to assess heat tolerance and including YP is important as lines with low SF but high YP and vice versa were identified under heat stress. Out of 49 SSR markers linked to spikelet fertility, 18 were validated for five traits. RM229 in wet season and RM430 and RM210 in dry season were significantly associated with both SF and its HSI under heat stress. RM430 was also significantly associated with both YP and its HSI in dry season. Thirty two candidate genes were identified close to nine markers associated with traits under heat stress.

Rice responses to rising temperatures--challenges, perspectives and future directions.

Phenotypic plasticity in overcoming heat stress-induced damage across hot tropical rice-growing regions is predominantly governed by relative humidity. Expression of transpiration cooling, an effective heat-avoiding mechanism, will diminish with the transition from fully flooded paddies to water-saving technologies, such as direct-seeded and aerobic rice cultivation, thus further aggravating stress damage. This change can potentially introduce greater sensitivity to previously unaffected developmental stages such as floral meristem (panicle) initiation and spikelet differentiation, and further intensify vulnerability at the known sensitive gametogenesis and flowering stages. More than the mean temperature rise, increased variability and a more rapid increase in nighttime temperature compared with the daytime maximum present a greater challenge. This review addresses (1) the importance of vapour pressure deficit under fully flooded paddies and increased vulnerability of rice production to heat stress or intermittent occurrence of combined heat and drought stress under emerging water-saving rice technologies; (2) the major disconnect with high night temperature response between field and controlled environments in terms of spikelet sterility; (3) highlights the most important mechanisms that affect key grain quality parameters, such as chalk formation under heat stress; and finally (4), we model and estimate heat stress-induced spikelet sterility taking South Asia as a case study.

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.

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.