OsNPF3.1,a nitrate,abscisic acid and gibberellin transporter gene,is essential for rice tillering and nitrogen utilization efficiency

Low-affinity nitrate transporter genes have been identified in subfamilies 4-8 of the rice nitrate transporter 1(NRT1)/peptide transporter family(NPF),but the OsNPF3 subfamily responsible for nitrate and phytohormone transport and rice growth and development remains unknown.In this study,we described OsNPF3.1 as an essential nitrate and phytohormone transporter gene for rice tillering and nitrogen utilization efficiency(NUtE).OsNPF3.1 possesses four major haplotypes of its promoter sequence in 517 cultivars,and its expression is positively associated with tiller number.Its expression was higher in the basal part,culm,and leaf blade than in other parts of the plant,and was strongly induced by nitrate,abscisic acid(ABA)and gibberellin 3(GA_3)in the root and shoot of rice.Electrophysiological experiments demonstrated that OsNPF3.1 is a pH-dependent low-affinity nitrate transporter,with rice protoplast uptake assays showing it to be an ABA and GA_3 transporter.OsNPF3.1 overexpression significantly promoted ABA accumulation in the roots and GA accumulation in the basal part of the plant which inhibited axillary bud outgrowth and rice tillering,especially at high nitrate concentrations.The NUtE of OsNPF3.1-overexpressing plants was enhanced under low and medium nitrate concentrations,whereas the NUtE of OsNPF3.1 clustered regularly interspaced short palindromic repeats(CRISPR)plants was increased under high nitrate concentrations.The results indicate that OsNPF3.1 transports nitrate and phytohormones in different rice tissues under different nitrate concentrations.The altered OsNPF3.1 expression improves NUtE in the OsNPF3.1-overexpressing and CRISPR lines at low and high nitrate concentrations,respectively.

The auxin transporter OsAUX1 regulates tillering in rice(Oryza sativa)

Tillering is an important agronomic trait of rice(Oryza sativa)that affects the number of effective panicles,thereby affecting yields.The phytohormone auxin plays a key role in tillering.Here we identified the high tillering and semi-dwarf 1(htsd1)mutant with auxin-deficiency root characteristics,such as shortened lateral roots,reduced lateral root density,and enlarged root angles.htsd1 showed reduced sensitivity to auxin,but the external application of indole-3-acetic acid(IAA)inhibited its tillering.We identified the mutated gene in htsd1 as AUXIN1(OsAUX1,LOC_Os01g63770),which encodes an auxin influx transporter.The promoter sequence of OsAUX1 contains many SQUAMOSA PROMOTER BINDING PROTEIN-LIKE(SPL)binding sites,and we demonstrated that SPL7 binds to the OsAUX1 promoter.TEOSINTE BRANCHED1(OsTB1),a key gene that negatively regulates tillering,was significantly downregulated in htsd1.Tillering was enhanced in the OsTB1 knockout mutant,and the external application of IAA inhibited tiller elongation in this mutant.Overexpressing OsTB1 restored the multi-tiller phenotype of htsd1.These results suggest that SPL7 directly binds to the OsAUX1 promoter and regulates tillering in rice by altering OsTB1 expression to modulate auxin signaling.

Genetic and environmental control of rice tillering

Increasing tiller number is a target of high-yield rice breeding. Identification of tiller-defect mutants and their corresponding genes is helpful for clarifying the molecular mechanism of rice tillering. Summarizing research progress on the two processes of rice tiller formation, namely the formation and growth of axillary meristem, this paper reviews the effects of genetic factors, endogenous hormones, and exogenous environment on rice tillering, finding that multiple molecular mechanisms and signal pathways regulating rice tillering cooperate rice tillering, and discusses future research objectives and application of its regulatory mechanism. Elucidation of theis mechanism will be helpful for breeding high-yielding rice cultivars with ideal plant type via molecular design breeding.

Tiller fertility is critical for improving grain yield,photosynthesis,and nitrogen efficiency in wheat

Genetic improvement has promoted wheat’s grain yield and nitrogen use efficiency(NUE)during the past decades.Therefore,the current wheat cultivars exhibit higher grain yield and NUE than previous cultivars in the Yangtze River Basin,China since the 2000s.However,the critical traits and mechanisms of the increased grain yield and NUE remain unknown.This study explores the mechanisms underlying these new cultivars’increased grain yield and NUE by studying 21 local cultivars cultivated for three growing seasons from 2016 to 2019.Significantly positive correlations were observed between grain yield and NUE in the three years.The cultivars were grouped into high(HH),medium(MM),and low(LL)grain yield and NUE groups.The HH group exhibited significantly high grain yield and NUE.High grain yield was attributed to more effective ears by high tiller fertility and greater single-spike yield by increasing post-anthesis single-stem biomass.Compared to other groups,the HH group demonstrated a longer leaf stay-green ability and a greater flag leaf photosynthetic rate after anthesis.It also showed higher N accumulation at pre-anthesis,which contributed to increasing N accumulation per stem,including stem and leaf sheath,leaf blade,and unit leaf area at pre-anthesis,and promoting N uptake efficiency,the main contribution of high NUE.Moreover,tiller fertility was positively related to N accumulation per stem,N accumulation per unit leaf area,leaf stay-green ability,and flag leaf photosynthetic rate,which indicates that improving tiller fertility promoted N uptake,leaf N accumulation,and photosynthetic ability,thereby achieving synchronous improvements in grain yield and NUE.Therefore,tiller fertility is proposed as an important kernel indicator that can be used in the breeding and management of cultivars to improve agricultural efficiency and sustainability.

Advances in studies on the physiological and molecular regulation of barley tillering

Tillering is a crucial trait closely associated with yield potential and environmental adaptation in cereal crops,regulated by the synergy of endogenous(genetic)and exogenous(environmental)factors.The physiological and molecular regulation of tillering has been intensively studied in rice and wheat.However,tillering research on barley is scarce.This review used the recent advances in bioinformatics to map all known and potential barley tiller development genes with their chromosomal genetic and physical positions.Many of them were mapped for the first time.We also discussed tillering regulation at genetic,physiological,and environmental levels.Moreover,we established a novel link between the genetic control of phytohormones and sugars with tillering.We provided evidence of how environmental cues and cropping systems help optimize the tiller number.This comprehensive review enhances the understanding of barley’s physiological and genetic mechanisms controlling tillering and other developmental traits.

PROG1 acts upstream of LAZY1 to regulate rice tiller angle as a repressor

Rice tiller angle,as a component of plant architecture,affects rice grain yield via plant density.However,the molecular mechanism underlying rice tiller angle remains elusive.We report that the key domestication gene PROSTRATE GROWTH 1(PROG1)controls rice tiller angle by regulating shoot gravitropism and LAZY1(LA1)-mediated asymmetric distribution of auxin.Acting as a transcriptional repressor,PROG1 negatively regulates the expression of LA1 in light-grown rice seedlings.Overexpression of LA1 partially rescued the larger tiller angle of the PROG1 complementation transgenic plant(prog1-D).Double-mutant analysis showed that PROG1 acts upstream of LA1 to regulate shoot gravitropism and tiller angle.Mutation of Suppressors of lazy1(SOL1),encoding DWARF3(D3)acting in the strigolactone signal pathway,suppressed the large tiller angle of prog1-D by rescuing the transcription of LA1.The discovery of a light-sensitive PROG1-LA1 transcription regulatory module controlling rice shoot gravitropism and tiller angle sheds light on the genetic control of rice tiller angle.

Identification of the candidate gene controlling tiller angle in common wheat through genome-wide association study and linkage analysis

Wheat tiller angle(TA)is an important agronomic trait that contributes to grain production by affecting plant architecture.It also plays a crucial role in high-yield wheat breeding.An association panel and a recombinant inbred line(RIL)population were used to map quantitative trait loci(QTL)for TA.Results showed that 470 significant SNPs with 10.4%–28.8%phenotypic variance explained(PVE)were detected in four replicates by a genome-wide association study(GWAS).Haplotype analysis showed that the TA_Hap_4B1 locus on chromosome 4B was a major QTL to regulate wheat TA.Ten QTL were totally detected by linkage mapping with the RIL population,and QTA.hau-4B.1 identified in six environments with the PVE of 7.88%–18.82%was a major and stable QTL.A combined analysis demonstrated that both TA_Hap_4B1 and QTA.hau-4B.1 were co-located on the same region.Moreover,QTA.hau-4B.1 was confirmed by bulked segregant RNA-Seq(BSR-Seq)analysis.Phenotypic analysis showed that QTA.hau-4B.1was also closely related to yield traits.Furthermore,Traes CS4B02G049700 was considered as a candidate gene through analysis of gene sequence and expression.This study can be potentially used in cloning key genes modulating wheat tillering and provides valuable genetic resources for improvement of wheat plant architecture.

Does Selection for Seedling Tiller Number in Perennial Biomass Feedstocks Translate to Yield and Quality Improvements in Mature Swards?

Breeding for seedling traits in herbaceous perennial biomass feedstocks that translate into increased biomass yield or quality in established swards could accelerate the development of perennial grass cultivars for bioenergy or forage. In previously reported research, breeding for single large tillers (ST) or multiple tillers (MT, ≥3) six weeks after planting for two generations in big bluestem (Andropogon gerardii Vitman) and switchgrass (Panicum virgatum L.) base populations produced ST and MT populations that differed significantly for seedling and mature plant traits including biomass yield in spaced planted nurseries. Our objective was to evaluate these ST and MT populations in sward trials to determine the effect of these genetic changes on biomass yield and quality when the plants were grown in competitive sward conditions. Big bluestem monocultures of the base, ST, and MT populations were evaluated at three locations in Nebraska in 2001 and 2002 as randomized complete block experiments with four replicates. Switchgrass monocultures of the base, ST, and MT populations were evaluated in 2003, 2004, and 2005 near Mead, NE as a randomized complete block with six replicates. In both big bluestem and switchgrass, the ST and MT populations did not consistently differ from the base population or each other for biomass yield or forage quality. These results demonstrate the importance of evaluating perennial grasses in sward trials and not relying solely on greenhouse-grown plants or space-planted nurseries to develop selection criteria and make selection decisions.

Yield and tillering response of super hybrid rice Liangyoupeijiu to tillage and establishment methods

Tillering is an important agronomic trait for rice grain production. To evaluate yield and tillering response, Liangyoupeijiu(super hybrid rice) was grown in Hunan, China during 2011–2012 under different methods of tillage(conventional and no-tillage system) and crop establishment methods(transplanting at a spacing of 20 cm × 20 cm with one seedling per hill and direct seeding at a seeding rate of 22.5 kg ha-1). Our results revealed that, at maximum tillering(Max.) and at maturity(MA) stages, direct seeding(DS) resulted in 22% more tillers than transplanting(TP) irrespective of tillage system. Tiller mortality reached a peak between panicle initiation(PI) and booting(BT) stages, and was 16% higher under conventional tillage(CT) than under no-tillage(NT). Transplanting required 29% more time for the completion of tillering and less for DS. Tillering rate was 43% higher in DS than TP under either CT or NT. There was a positive correlation between panicle number per m2and maximum tiller number per m2, but not panicle-bearing tiller rate. The panicle bearing tiller rate was higher under DS than TP and higher under NT than CT. Tiller dry weight gradually increased up to heading(HD) stage, and was 14% higher under TP than DS. Leaf area(cm2tiller-1) gradually increased from Max. to HD stage and then decreased by 34% in conventional tillage transplanting(CTTP) and 45% in no-tillage transplanting(NTTP) from 12DAH–24DAH(days after heading), but was similar(35%) under DS under either CT or NT. Grain yield was higher under CTTP owing to the larger sink size(heavier panicle, more spikelets in per cm length of panicle) than under DS.

Effects of key growth conditions on endogenous hormone content in tillering stem bases,germination of lateral buds,and biomass allocation in Indocalamus decorus

Physiological responses and changes in growth of Indocalamus decorus Q.H.Dai under different ecological conditions are essential for further understanding growth regulation and adaptive mechanisms and establishing an evidence-based management system for optimal growth. In this study, the endogenous hormone content in tillering stem bases, germination of lateral buds, and biomass allocation of this bamboo species in different growth environments were investigated. Among the endogenous hormones in the basal stems of tillers, indole-3-pyruvic acid and zeatin riboside were highly correlated with lateral buds that germinated to form shoots, while gibberellic acid was highly correlated with lateral buds that germinated to form rhizomes. The best lateral bud germination characteristics were achieved with full sun, a density of six plantlets per pot, and watering every 6 days. I. decorus plantlets used different resource allocation strategies depending on treatment. Different ecological factors influenced endogenous hormones in the bamboo stem base,which affected lateral bud germination and biomass allocation.

GNP6,a novel allele of MOC1,regulates panicle and tiller development in rice

The yield of rice is mostly affected by three factors,namely,panicle number,grain number and grain weight.Variation in panicle and grain numbers is mainly caused by tiller and panicle branches generated from axillary meristems(AMs).MOC1 encodes a putative GRAS family nuclear protein that regulates AM formation.Although several alleles of MOC1 have been identified,its variation in germplasm resources remains unclear.In the present study we characterized a novel mocl allele named gnp6 which has a thymine insertion in the coding sequence of the SAW motif in the GRAS domain.This mutation causes arrested branch formation.The SAW motif is necessary for nuclear localization of GNP6/MOC1 where it functions as a transcription factor or co-regulator.Haplotype analysis showed that the coding region of GNP6/MOC1 was conserved without any non-synonymous mutations in 240 rice accessions.However,variation in the promoter region might affect the expression of it and its downstream genes.Joint haplotype analysis of GNP6/MOC1 and MOC3 showed that haplotype combinations H9,H10 and H11,namely MOC1-Hap1 in combination with MOC3-Hap3,MOC3-Hap4 or MOC3-Hap5 could be bred to promote branch formation.These findings will enrich the genetic resources available for rice breeders.

Genetic, hormonal, and environmental control of tillering in wheat

Tillering contributes greatly to grain yield in wheat.Investigating the mechanisms of tillering provides a theoretical foundation and genetic resources for the molecular breeding of wheat.The regulation of tillering is a complex molecular process that involves a multitude of factors.Little is known about the molecular mechanisms in the wheat genome,although progress has been made in rice.Here we review the developmental characteristics of tillers and summarize current knowledge of the roles of endogenous and environmental factors in wheat tillering.We propose directions for future studies and advanced technologies to be used for gene identification and functional studies.

Straw mulch-based no-tillage improves tillering capability of dryland wheat by reducing asymmetric competition between main stem and tillers

The moisture-conserving effect of straw mulch-based no-tillage(SMNT)is expected to increase fertile spikes and grain yield in environments with rainfall less than 200 mm.However,the mechanisms under-lying the positive effect of SMNT on wheat tillering are not fully elucidated.A split-plot experiment was designed to investigate the combined effects of SMNT and cultivars on tillering of dryland wheat grown under both dry and favorable climates.Application of SMNT to a cultivar with 1-2 tillers exploited both tillering and kernel-number plasticity,increasing the mean grain yield by 20.5%.This increase was attrib-uted primarily to an increased first-tiller emergence rate resulting from increased N uptake,leaf N con-tent,and N remobilization from tillers to their grain.The second and third tillers,as transient sinks,contributed to the tiller survival rate,which depends on tiller leaf number.The increased total N uptake by SMNT also increased the dry mass yield of tillers and the C:N ratio,reducing the asymmetric compe-tition between main stem and tillers.Owing to these beneficial effects,reduced mitogen-activated pro-tein kinase(MAPK)and abscisic acid signals were observed under SMNT,whereas indole-3-acetic acid(IAA)signals and genes involved in DNA replication and mismatch repair were increased.These signals activated three critical transcription factors(the calmodulin-binding transcription activator,GRAS domain,and cysteine-2/histidine-2 family)and further increased rapid drought response and tiller main-tenance after stem extension.Phenylpropanoid biosynthesis,sphingolipid biosynthesis,and galactose metabolism were most relevant to increased tillering under SMNT because of their critical role in drought response and lignin biosynthesis.Our results suggest that straw mulch-based no-tillage activates rapid drought response and improved wheat tillering by coordinating root N uptake,N remobilization,and asymmetric competition between main stem and tillers.

Studies on the Developmental Genetics of Tiller Number in Three-line Indica Hybrid Rice

Following NC Ⅱ design, the developmental genetic behavior of tiller number (TN) in three-line indica hybrid rice was studied using additive-dominance developmental genetic models and the corresponding statistical methods. The results showed that dominance effects were predominant for TN. The expression of those additive effects were affected by environment and genotype interaction, but the expression of dominance effects were not affected. Heterosis was the strongest in the middle developmental periods of TN. Additive effects and dominance effects were selectively expressed throughout in the entire tillering developmental stage.Analysis of genetic correlation between TN at different stages and the productive panicles indicated that a close correlation appeared earlier in the populations with higher heterosis than in those with less heterosis. Utilization of heterosis at the middle tillering stage might enhance the final biomass but reduce the percentage of productive panicles.

The chloroplast-localized protein LTA1 regulates tiller angle and yield of rice

Plant architecture strongly influences rice grain yield.We report the cloning and characterization of the LTA1 gene,which simultaneously controls tiller angle and yield of rice.LTA1 encodes a chloroplastlocalized protein with a conserved YbaB DNA-binding domain,and is highly expressed in photosynthetic tissues including leaves and leaf sheaths.Disrupting the function of LTA1 leads to large tiller angle and yield reduction of rice.LTA1 affects the gravity response by mediating the distribution of endogenous auxin,thereby regulating the tiller angle.An lta1 mutant showed abnormal chloroplast development and decreased chlorophyll content and photosynthetic rate,in turn leading to reduction of rice yield.Our findings shed light on the genetic basis of tiller angle and provide a potential gene resource for the improvement of plant architecture and rice yield.

Variation in Senescence Pattern of Different Classes of Rice Tillers and Its Effect on Panicle Biomass Growth and Grain Yield

In rice, the initiation of tillers is staggered and temporally spaced, but maturity is synchronous. Duration of growth in a later-initiated tiller on a higher culm node is shorter and it contributes less biomass and grain yield. The present investigation attempts to discover the manner in which ordered pattern of senescence in basipetal succession impacts source capacity of tillers in two contrasting rice cultivars, namely Lalat (high tillering) and MGD-106 (medium tillering) during the dry season of 2009 and ascertain how tiller production capacity influences dry matter partitioning and tiller dynamics of the plant. In both the rice cultivars, the progress of senescence among different types of tillers was indicated by gradual decline of photosynthetic pigments, total nitrogen and protein concentrations and increase of lipid peroxidation and peroxidase activity of the flag leaf, which affected photosynthetic efficiency. The effects were more pernicious on the newer tillers compared to older tillers. It was observed that metabolic dominance of the older tillers over newer tillers could be accrued due to higher photosynthetic source capacity of the former than that of the latter. It was concluded that flag leaf of a later-initiated tiller is less tolerant to senescence induced photo-oxidative stress, which decreases both source and sink activities. Increase of tiller number and order in rice increases vulnerability of the later-initiated tillers for oxidative stress and grain filling.

Effects of Seed Soaking with Paclobutrazol on Tillering and Physio-logical Characteristics of Sugarcane Seedlings

In order to study the effects of seed soaking with Paclobutrazol( PP333) on the tillering and physiological characteristics of sugarcane seedlings,sugar cane variety ROC22 was used as experimental material. The effects of seed soaking with different concentrations of PP333 were studied. The tiller number and growth of sugarcane were surveyed at the 6-leaf stage,the physiological indicators such as chlorophyll content,soluble protein content,proline content and peroxidase activity were measured at the 2-leaf,4-leaf,and 6-leaf stages. The results showed that the seed soaking with PP333 can effectively improve the tillering of sugarcane seedlings. The suitable concentration for the tillering of sugarcane and the growth and development of sugarcane was of 50 mg/L; the seed soaking with PP333 significantly increased the chlorophyll,soluble protein,proline,and peroxidase activity of leaves of sugarcane seedlings; the content of chlorophyll and soluble protein in leaves of sugarcane seedlings treated with 90 mg/L PP333 was the highest,and the proline content and peroxidase activity of sugarcane treated with 50 mg/L PP333 were the highest.

Effects of gibberellic acid on tiller-bulb number and growth performance of Lilium davidii var. unicolor

Lilium davidii var.unicolor(Lanzhou lily)is an important economic crop in the northwest cold and arid regions of China.Effective regulation of tiller-bulb development and plant growth is the key to improving yield and quality of the lily.This study attempted to evaluate the effect of gibberellic acid(GA3)on tiller-bulb development and plant growth of Lanzhou lily by applying GA3 at various concentrations(0 mg/L,10 mg/L,30 mg/L,60 mg/L,and 100 mg/L)before planting and in the seedling period.Results showed that the 60-mg/L GA3 application had an inhibiting effect on tiller-bulb formation and increased the ratios of single and double bulbs but decreased the ratios of bulbs with three or more tiller bulbs,as com pared to the control(CK)and other GA3 treatments.The difference in flower number did not reach significant levels among the treatments.The tillering-related endogenous hormones IAA(indole-3-acetic acid)and Z(zeatin)content de creased,while IAA/Z increased with the 60-mg/L GA3 treatment during tiller initiation.And also,the shoot-bulb number and total daughter-bulb number decreased significantly with the 60-mg/L GA3 treatment.Furthermore,the 10-mg/L GA3 application promoted growth of Lanzhou lily significantly and resulted in an increase in plant height;bulb diameter;bulb circumference;and biomass of shoots,bulbs,fibrous roots,and the whole plant.Therefore,GA3 application is promising as a new regulation method for inhibiting tiller-bulb development and promoting bulb growth in Lanzhou lily production.

Divergent responses of tiller and grain yield to fertilization and fallow precipitation:Insights from a 28-year long-term experiment in a semiarid winter wheat system

Tillering is an important phenological stage,which is strongly related to the yield in spike components and final grain yield during winter wheat growth.Precipitation during the fallow season(fallow precipitation)influences tillering in winter wheat on the semi-arid Chinese Loess Plateau.However,little work has been done regarding tiller number changes under various types of fertilization and amounts of fallow precipitation on a long-term scale.Effects of fallow precipitation and fertilization on tiller were investigated in a winter wheat(Triticum aestivum L.)system in a 28-year field study(1990 to 2017)in a semiarid agro-ecosystem.Tiller number,spike number and grain yield were measured in four fertilization conditions:control without fertilizer(CK);mineral nitrogen fertilizer alone(N);mineral phosphorus fertilizer alone(P);mineral nitrogen and phosphorus fertilizer together(NP).Based on the long-term annual fallow precipitation,dry years(mean annual fallow precipitation)were distinguished.Phosphorus fertilization alone significantly increased the mean annual tiller number(23%),and the increase in tiller number was higher in wet years(29%)than in the dry years(17%).However,nitrogen fertilization alone had little effect on mean tiller number,while nitrogen and phosphorus together significantly increased mean annual tiller number(30%),mean tiller number in wet years(45%)and mean tiller number in dry years(17%).Tiller number was significantly and positively correlated with fallow precipitation in dry years for all fertilizer treatments,whereas it was weakly and either positively or negatively correlated with fallow precipitation in wet years depending on the treatment.This study found positive correlations between tiller number and fallow precipitation in the CK and NP treatments,and it found negative correlations between tiller number and fallow precipitation in the treatments with nitrogen fertilization alone or phosphorous fertilization alone in wet years.Understanding the impacts of fallow precipitation and fertilization on tiller development shed light on ways to improve crop production in rain-fed agricultural regions.

A Standardized Method for Determining Tillering Capacity of Wheat Cultivars

Genotype and agronomic management greatly influence crop growth and grain yield in wheat (Triticum aestivum L.). To ensure sustainable production, seeding rate selection is important to maximize efficiency of every plant. Tillering can allow wheat plants to adjust growth relative to plant density and quality of growing conditions. This research sought to determine a method for assessing tillering of wheat cultivars and develop a standardized approach for characterizing cultivar tillering capacity. Nine cultivars with diverse genetic and phenotypic characteristics were seeded in 2017-2018 at Prosper, ND using various seeding techniques at differing plant spacing arrangements to evaluate tillering habit and spikes plant-1. Cultivars grown at population densities common in grower fields did not express full tillering potential. Spaced-plantings of cultivars promoted cultivar expression of tillering phenotype. The SOFATT (seed only a few, and then thin) method, where average spikes plant-1 was determined from multiple plants sampled from a cultivar grown at spaced-plantings (inter-row and intra-row spacing at 30 ± 12 cm), is recommended to properly assess tillering habits of wheat cultivars. Breeders and researchers can use results from SOFATT evaluations to determine tillering capacity rating for each cultivar based on raw or transformed z-score values for spikes plant-1.