A novel single-base mutation in CaSGR1 confers the stay-green phenotype in pepper

The stay-green trait is of considerable importance in extending the shelf life of green pepper fruit(Capsicum annuum L.)and in enhancing the appearance of ornamental plants.The study revealed the genetic and regulatory mechanisms of the stay-green trait in pepper,which will aid in the selection of ornamental pepper varieties.In this study,a pepper mutant with stay-green fruit named TNX348 was identified from a germplasm resource bank.Two segregating populations were constructed using the stay-green mutant TNX348 and then used in bulked segregant analysis combined with RNA sequencing and linkage analyses.The causal gene of the stay-green trait was mapped to an approximately 131-kb region,and a senescence-induced chloroplast protein gene,CaSGR1(Capana01g000359),was identified as a candidate gene.Sequencing analysis revealed a G→A single-base mutation of CaSGR1 in TNX348 that led to early termination of translation.Based on the single-base mutation,a single nucleotide polymorphism(SNP)marker co-segregating with the stay-green trait was developed.Furthermore,in transcriptome analysis,expression patterns of 11 hormone transduction-related transcription factors,such as abscisic acid-insensitive(ABI),abscisic acidresponsive element-binding factor(ABF),and NAC transcription factor,were similar or opposite to that of CaSGR1.The results indicated that the transcription factors might mediate chlorophyll degradation by regulating the expression of CaSGR1.

Maize-soybean relay cropping increases soybean yield synergistically by extending the post-anthesis leaf stay-green period and accelerating grain filling

Relay cropping of Poaceae and Fabaceae promotes high yield and land-use efficiency by allowing a double harvest.However,it is difficult to increase yield synergistically because of the reduced photosynthetic abilities of legume leaves under the shade of graminoids.Leaf photosynthetic capacity in relay cropping systems is associated with ecological niche differentiation and photosynthetic compensation after restoration of normal light.We conducted a field experiment in southwest China in 2020–2021 to evaluate the effects of three cropping patterns:maize–soybean relay cropping(IMS),monoculture maize(MM),and monoculture soybean(SS),and N application levels:no N application(NN:0 kg N ha^(−1)),reduced N(RN:180 kg N ha^(−1)),and conventional N(CN:240 kg N ha^(−1)).Compared to monocropping,relay cropping increased the stay-green traits of maize and soybean by 13%and 89%,respectively.Relay cropping prolonged the leaf stay-green duration in the maize and soybean lag phase by almost 4 and 8 days,respectively.Relay cropping maize(IM)increased the leaf area index(LAI)by 79.4%to 88.5%under NN and 55.5%to 148%under RN.Relay cropping soybean(IS)increased the LAI from 115%to 437%at days 40 to 50 after anthesis.IM increased yield by 65.6%.IS increased yield by 9.7%.HI and system yield were at their highest values under RN.In the relay cropping system,reduced N application extended green leaf duration,increased photosynthesis inside the canopy at multiple levels,ultimately increases soybean yield synergistically.

Arabidopsis STAY-GREEN2 Is a Negative Regulator of Chlorophyll Degradation during Leaf Senescence

Chlorophyll （Chl） degradation causes leaf yellowing during senescence or under stress conditions. For Chl breakdown, STAY-GREEN1 （SGR1） interacts with Chl catabolic enzymes （CCEs） and light-harvesting complex II （LHCII） at the thylakoid membrane, possibly to allow metabolic channeling of potentially phototoxic Chl breakdown intermediates. Among these Chl catabolic components, SGR1 acts as a key regulator of leaf yellowing. In addition to SGR1 （At4g22920）, the Arabidopsis thaliana genome contains an additional homolog, SGR2 （At4g11910）, whose biological function remains elusive. Under senescence-inducing conditions, SGR2 expression is highly up-regulated, similarly to SGR1 expression. Here we show that SGR2 function counteracts SGR1 activity in leaf Chl degradation; SGR2-overexpressing plants stayed green and the sgr2-1 knockout mutant exhibited early leaf yellowing under age-, dark-, and stress-induced senescence conditions. Like SGR1, SGR2 interacted with LHCII but, in contrast to SGR1, SGR2 interactions with CCEs were very limited. Furthermore, SGR1 and SGR2 formed homo- or heterodimers, strongly suggesting a role for SGR2 in negatively regulat- ing Chl degradation by possibly interfering with the proposed CCE-recruiting function of SGR1. Our data indicate an antagonistic evolution of the functions of SGR1 and SGR2 in Arabidopsis to balance Chl catabolism in chloroplasts with the dismantling and remobilizing of other cellular components in senescing leaf cells.

桃PpSGR基因功能鉴定及其对乙烯合成的调控

【目的】乙烯合成及果肉褪绿是桃果实成熟过程中相伴出现的两个生理事件。STAY-GREEN(SGR)是参与植物叶片和果实褪绿的重要基因。然而,桃SGR基因在果实成熟及褪绿过程中的功能尚不清晰,旨在初步探究PpSGR基因在桃果实成熟及褪绿过程中的功能。【方法】以秋蜜红为试验材料,对PpSGR基因进行克隆,对PpSGR的核苷酸及氨基酸序列进行分析,对不同发育时期桃果肉中PpSGR的转录水平进行检测,并对PpSGR基因调控叶绿素降解及乙烯合成的功能进行研究。【结果】PpSGR编码区全长为831 bp;该基因编码的蛋白序列含有1个高度保守的SGR域。PpSGR基因的表达水平随着果肉逐渐褪绿呈现上升的趋势。瞬时过表达PpSGR基因后,桃叶片颜色明显褪绿,并且在300 mmol·L-1NaCl的盐胁迫下,过表达PpSGR的叶片褪绿更加明显。此外,过表达PpSGR后,桃苗乙烯合成的限速基因PpACS1、PpACS4及PpACS6均表达上调,且内源乙烯释放量显著增多。【结论】对PpSGR的基因功能进行鉴定和研究,并分析了其对乙烯的调控作用,为进一步解析桃果实成熟及果肉褪绿提供了新的思路,也为不同成熟期桃品种的选育提供了理论基础。

Wheat leaf senescence and its regulatory gene network

Wheat leaf senescence is a developmental process that involves expressional changes in thousands of genes that ultimately impact grain protein content(GPC), grain yield(GY), and nitrogen use efficiency.The onset and rate of senescence are strongly influenced by plant hormones and environmental factors e.g. nitrogen availability. At maturity, decrease in nitrogen uptake could enhance N remobilization from leaves and stem to grain, eventually leading to leaf senescence. Early senescence is related to high GPC and somewhat low yield whereas late senescence is often related to high yield and somewhat low GPC. Early or late senescence is principally regulated by up and down-regulation of senescence associated genes. Integration of external and internal factors together with genotypic variation influence senescence associated genes in a developmental age dependent manner. Although regulation of genes involved in senescence has been studied in rice, Arabidopsis, maize, and currently in wheat, there are genotypespecific variations yet to explore. A major effort is needed to understand the interaction of positive and negative senescence regulators in determining the onset of senescence. In wheat, increasing attention has been paid to understand the role of positive senescence regulator, e.g. GPC-1, regulated gene network during early senescence time course. Recently, gene regulatory network involved early to late senescence time course revealed important senescence regulators. However, the known negative senescence regulator Ta NAC-S gene has not been extensively studied in wheat and little is known about its value in breeding. Existing data on senescence-related transcriptome studies and gene regulatory network could effectively be used for functional study in developing nitrogen efficient wheat varieties.

Agronomic Management Strategies to Reduce the Yield Loss Associated with Spring Harvested Corn in Ontario

Some growers in northern corn (Zea mays L.) producing regions forgo the typical autumn harvest for various reasons, but not without the risk of significant yield loss. Therefore, strategies are needed for managing the risks to yield when harvesting corn in spring. Field experiments, with various management strategies, were initiated in Ontario, Canada near Belmont and Ridgetown in 2009 and near Belmont, Ridgetown, and Lucan in 2010. Management strategies investigated the use of hybrids with a range in maturity, the use of standard and reduced plant populations, and the use of a foliar fungicide applied around tasseling. The parameters examined were stay-green in autumn, lodging in spring, and grain yield, moisture, and test weight of corn harvested in autumn and spring. Standard corn production practices consist of using a full-season hybrid planted at 80,000 plants&middotha-1 with no late-season fungicide application;however, if over-wintered at Belmont, corn managed using these practices resulted in a 23.1% yield loss (12.1 vs 9.3 Mg&middotha-1) averaged across years when the crop was harvested in the spring. An overwintering management strategy for corn was identified, which consisted of planting at a reduced plant population (60,000 plants&middotha-1) and spraying the crop with QUILT&reg (azoxystrobin + propiconazole at 200 g a.i. ha-1) at the VT to R1 growth stage. Averaged across all hybrids, this strategy minimized yield losses through improvements on corn standability with only a 3.5% yield loss at Ridgetown and a 13.2% yield loss at Belmont. Furthermore, grain test weights for corn with the overwintering strategy were similar to or greater than corn overwintered with the standard production practice. However, weather conditions have the potential to overwhelm any management strategy. In spite of the favorable data indicating reduced risks with a spring harvest, lodging was still higher than expected and yield losses would likely be unacceptable for most growers to make a spring corn harvest a widely accepted practice, unless autumn grain moistures are extremely high, drying charges are high, and if stalk strength going into the winter was exceptional.

Grain Sink Strength Related to Carbon Staying in the Leaves of Hybrid Wheat XN901

XN901 is a K-type three-line hybrid wheat with a high yield potential, and its leaves and stem remaining green during grain maturation, suggesting much assimilate stay in leaves and stem. The grain water content, grain volume, carbohydrate content, and enzyme activity of sucose metabolism in the grain, as well as source-sink relationship were studied in order to investigate the physiological reason of the assimilate remaining in leaves and stem at the late stage. The results showed that the hybrid grains had more water and soluble sugar, higher activities of acid invertase and sucrose synthase at the early stage that led to a faster expansion growth, greater grain volume and faster starch synthesis at the early to mid stage of grain development. Also it had a longer period for actively filling. As a result, the grain weight and yield of the hybrid were increased by 14 and 15% respectively compared to that of Shaan 229. Additionally, the biomass of XN901 was 41.7% more than that of control, but its harvest index was 9% lower than Shaan 229. However, its lower activity of sucrose synthase indicated a lower sink activity at the late stage, resulting in a slow rate of filling and starch synthesis. Also, the hybrid wheat XN901 had a large source-sink ratio. It is the main reason for much assimilate remaining in the straw at the late stage and lower harvest index. Strengthening the sink activity and raising the harvest index should be the key means of improving the yield of hybrid wheat.

叶绿素降解过程中SGRs蛋白表达调控和功能分析的研究进展

虽然叶绿素(Chl)的降解过程和6种Chl降解酶(CCEs)现在都已有深入了解,但在拟南芥中发现滞绿基因(SGRs)对植物衰老起关键调控作用。SGRs蛋白的同系物SGR1和SGRL过表达促进Chl降解,而SGR2起反作用,从而实现Chl代谢的平衡。最新研究表明在拟南芥中发现SGRs编码脱镁螯合酶(MCS),能嵌入到Chl-蛋白酶复合体中提取Mg^(2+),具有酶的活性。这项研究打破了原有的脱Mg^(2+)过程是由小分子物质酸性条件自发进行的观点。另外,对于SGRs表达调控的研究也取得了一定进展。研究发现SGRs蛋白的表达能被ABA触发,而ABIs转录因子是ABA信号转导的效应器。因此ABIs能结合在SGRs启动子上的ABA响应元件,进而调控SGRs蛋白的表达,对Chl的降解起关键作用。

Identification of Differentially Senescing Mutants of Wheat and Impacts on Yield,Biomass and Nitrogen Partitioning

Increasing photosynthetic capacity by extending canopy longevity during grain filling using slow senescing stay-green genotypes is a possible means to improve yield in wheat. Ethyl methanesulfonate （EMS） mutated wheat lines （Triticum aestivum L. cv. Paragon） were screened for fast and slow canopy senescence to investigate the impact on yield and nitrogen partitioning. Stay-green and fast-senescing lines with similar anthesis dates were characterised in detail. Delayed senescence was only apparent at higher nitrogen supply with low nitrogen supply enhancing the rate of senescence in all lines. In the stay-green line 3 （SG3）, on a whole plant basis, tiller and seed number increased whilst thousand grain weight （TGW） decreased; although a greater N uptake was observed in the main tiller, yield was not affected. In fast-senescing line 2 （FS2）, yield decreased, principally as a result of decreased TGW. Analysis of N-partitioning in the main stem indicated that although the slow-senescing line had lower biomass and consequently less nitrogen in all plant parts, the proportion of biomass and nitrogen in the flag leaf was greater at anthesis compared to the other lines; this contributed to the grain N and yield of the slow-senescing line at maturity in both the main tiller and in the whole plant. A field trial confirmed senescence patterns of the two lines, and the negative impact on yield for FS2 and a positive impact for SG3 at low N only. The lack of increased yield in the slow-senescing line was likely due to decreased biomass and additionally a possible sink limitation.

Mutation of Oryza sativa CORONATINE INSENSITIVE 1b(OsCOI1b) delays leaf senescence

Jasmonic acid （JA） functions in plant development, including senescence and immunity. Arabidopsis thaliana CORONATINE INSENSITIVE 1 encodes a JA receptor and functions in the JA‐responsive signaling pathway. The Arabidopsis genome harbors a single COI gene, but the rice （Oryza sativa） genome harbors three COI homologs, OsCOI1a, OsCOI1b, and OsCOI2. Thus, it remains unclear whether each OsCOI has distinct, additive, synergistic, or redundant func-tions in development. Here, we use the oscoi1b‐1 knockout mutants to show that OsCOI1b mainly affects leaf senescence under senescence‐promoting conditions. oscoi1b‐1 mutants stayed green during dark‐induced and natural senescence, with substantial retention of chlorophylls and photosyn-thetic capacity. Furthermore, several senescence‐associated genes were downregulated in oscoi1b‐1 mutants, including homologs of Arabidopsis thaliana ETHYLENE INSENSITIVE 3 and ORESARA 1, important regulators of leaf senescence. These results suggest that crosstalk between JA signaling and ethylene signaling affects leaf senescence. The Arabidopsis coi1‐1 plants containing 35S：OsCOI1a or 35S：OsCOI1b rescued the delayed leaf senescence during dark incubation, sug-gesting that both OsCOI1a and OsCOI1b are required for promoting leaf senescence in rice. oscoi1b‐1 mutants showed significant decreases in spikelet fertility and grain weight, leading to severe reduction of grain yield, indicating that OsCOI1‐mediated JA signaling affects spikelet fertility and grain filling.