Increased Tiller Number Research Articles

Swarna × Oryza nivara introgression lines: a resource for seedling vigour traits in rice

AbstractSeedling vigour is an important indicator of crop establishment, subsequent crop growth and yield. Initial seedling vigour is most vital in case of water-limited conditions and in environments where the crop is exposed to different stresses at the early growth stage. Wild and weedy species are well known for their vigour and survival in adverse environmental conditions. Seedling vigour traits of backcross introgression lines (BILs) derived from Swarna × Oryza nivara IRGC81848(S) (accession from Uttar Pradesh, India) and IRGC81832 (K) (accession from Bihar, India) were studied in wet (Kharif) and dry (Rabi) seasons. Seedling vigour was estimated in terms of plant height and tiller number at 30 and 60 d after transplanting under field conditions. In both the seasons, 148S showed highest seedling vigour for plant height. The highest number of tillers were produced by 7K in Kharif and 248S in Rabi season. 75S showed the highest percentage increase in tiller number consistently. High yielding BILs 166S, 14S and 148S showed higher seedling vigour indices compared with checks Tulasi and Sahbhagidhan. Seedling vigour was also evaluated using paper roll method and shoot length, root length and dry weight were used to estimate vigour index. Season-wise association studies were conducted to determine the relative contribution of seedling vigour to yield traits. Seedling vigour was significantly correlated with yield traits. Markers RM217 and RM253 on chromosome 6 differentiated lines with high seedling vigour from those with low seedling vigour and have the potential for use in marker-assisted breeding.

Modulation of plant architecture by the miR156f-OsSPL7-OsGH3.8 pathway in rice.

Tiller number and plant height are two of the main features of plant architecture that directly influence rice yield. Auxin and miR156, an extensively studied small RNA (smRNA), are both broadly involved in plant development and physiology, suggesting a possible relationship between the two. In this study, we identified a rice T-DNA insertion cluster and dwarf (cd) mutant that has an increased tiller number and reduced plant height. The T-DNA insertion was in close proximity to the miR156f gene and was associated with its up-regulation. Plants overexpressing miR156f resembled the cd mutant. In contrast, plants overexpressing an miR156f target mimic (MIM156fOE) had a reduced tiller number and increased height. Genetic analysis showed that OsSPL7 is a target of miR156f that regulates plant architecture. Plants overexpressing OsSPL7 had a reduced tiller number, while OsSPL7 RNAi plants had an increased tiller number and a reduced height. We also found that OsSPL7 binds directly to the OsGH3.8 promoter to regulate its transcription. Overexpression of OsGH3.8 and OsGH3.8 RNAi partially complemented the MIM156fOE and cd mutant phenotypes, respectively. Our combined data show that the miR156f-OsSPL7-OsGH3.8 pathway regulates tiller number and plant height in rice, and this pathway may allow crosstalk between miR156 and auxin.

CHLORIDE CHANNEL 1 promotes drought tolerance in rice, leading to increased grain yield

Plant chloride channels (CLCs) localize to the plasma and organellar membranes; these channels play pivotal roles in the modulation of ion homeostasis and cell turgor. Recent studies have shown that the expression of CLCs is involved in plant responses to environmental stress. Here, we examined the rice (Oryza sativa) tonoplast-localized channel OsCLC1. OsCLC1 is preferentially expressed in roots, and therefore, we generated transgenic rice with root-specific overexpression of OsCLC1 (RCc3::OsCLC1). We also identified a T-DNA mutant line that lacks expression of OsCLC1 (osclc1). We found that RCc3::OsCLC1 rice plants showed increased tiller number and grain yield, whereas the osclc1 plants exhibited decreased tiller number and grain yield, compared with wild type. These observations suggest that expression of OsCLC1 affects rice growth and productivity. Furthermore, RCc3::OsCLC1 plants showed enhanced drought tolerance, leading to increased grain yield compared to wild-type plants grown under the same conditions. By contrast, osclc1 mutants exhibited reduced drought tolerance and productivity compared to wild-type plants. When expression of OsCLC1 was analyzed in drought, jasmonic acid (JA) or abscisic acid (ABA)-treated rice, expression of OsCLC1 was preferentially upregulated in roots in response to drought and JA, and was preferentially upregulated in shoots in response to ABA. Together with the finding that expression of OsCLC1 is positively correlated both with expressions of OsDREB1A and OsbHLH148, key transcription factors in drought and JA responses, respectively, these results suggest that OsCLC1 regulates drought tolerance in rice and JA signaling is involved in this process.

Impact of Elevated CO<sub>2</sub> on <i>Oryza sativa</i> Phenology and Brown Planthopper, <i>Nilaparvata lugens</i> (Hemiptera:Delphacidae) Population

The impact of elevated CO 2 (570 ± 25 ppm) on brown planthopper, Nilaparvata lugens (Stal) and Pusa Basmati 1401 rice in comparison to ambient CO 2 was studied in open top chambers (OTCs) during the rainy seasons of 2013 and 2014. Crop canopy circumference was higher (13.1–16.8 cm) under elevated CO 2 when compared to ambient CO 2 (10.3–13.1 cm) during different rice phenological stages indicating the positive influence of elevated CO 2 . In addition, elevated CO 2 exhibited a positive effect on rice plants through increase in tiller number (17.6%), reproductive tiller number (16.2%), number of seeds/panicle (15.1%) and thousand grains weight (10.8%) that resulted in higher grain yield (15%) when compared to ambient CO 2 . Elevated CO 2 also exhibited a positive effect on brown planthopper population through increase in fecundity (29% and 31.6%) which resulted in a significant increase in its population to 150.3 ± 16.4 and 97.7 ± 8.7 hoppers/hill at peak incidence during 2013 and 2014 respectively, when compared to the corresponding 49.1 ± 9.3 and 43.7 ± 7.0 hoppers/hill under ambient CO 2 . Moreover, brown planthopper females excreted more honeydew (68.2% and 72.3%) under elevated CO 2 over ambient CO 2 during both years. However, elevated CO 2 caused reduction in the longevity of females (23.9–27.4%) during both years and male longevity (24.1%) during 2013. Despite the positive effect, rice crops suffered higher yield loss under elevated CO 2 (29.9–34.9%) due to increased brown planthopper infestation coupled with higher sucking rate due to reduced nitrogen level under elevated CO 2 compared to ambient CO 2 (17–23.1%) during 2013 and 2014.

Mutations in the MIT3 gene encoding a caroteniod isomerase lead to increased tiller number in rice

Carotenoids not only play important roles in light harvesting and photoprotection against excess light, but also serve as precursors for apocaroteniod hormones such as abscisic acid (ABA) and strigolactones (SLs). Although light- and ABA-associated phenotypes of the carotenoid biosynthesis mutants such as albino, leaf variegation and preharvest sprouting have been studied extensively, the SLs-related branching phenotype is rarely explored. Here we characterized four allelic rice mutants named mit3, which exhibited moderately increased tiller number, semi-dwarfism and leaf variegation. Map-based cloning revealed that MIT3 encodes a carotenoid isomerase (CRTISO), the key enzyme catalyzing the conversion from prolycopene to all-trans-lycopene in carotenoid biosynthesis. Prolycopene was accumulated while all-trans-lycopene was barely detectable in the dark-grown mit3 seedlings. Accordingly, content of lutein and β-carotene, the two most abundant carotenoids, was significantly reduced. Furthermore, content of epi-5DS, a native SL, was significantly reduced in mit3. Exogenously applied GR24, a synthetic SL, could rescue the tillering phenotype of mit3. Double mutant analysis of mit3 with the SLs biosynthesis mutant d17 revealed that MIT3 controls tiller development upstream of the SLs biosynthesis pathway. Our results reveal that the tillering phenotype of mit3 is due to SL deficiency and directly link carotenoid deficiency with SL-regulated rice tillering.

Semi-commercial scale production of carrageenan plant growth promoter by E-beam technology

The plant growth promoter (PGP) effect of different formulations of gamma-irradiated carrageenan solutions were tested on rice by foliar spraying. The best formulation was produced in large quantity for field application. Multilocation trials of around 1600ha rice field in different regions of the Philippines indicated increase in yield of an average of around 20%. Increased resistance to tungro virus was also noted. Likewise, there was extensive root growth, increase in number of tillers, and development of sturdy stems that prevented lodging of rice plant.E-beam irradiation of carrageenan PGP was also studied to increase its throughput of production. Degradation of carrageenan by e-beam irradiation is inhibited by the formation of crosslinks. Optimisation by addition of hydrogen peroxide to improve degradation is discussed. A continuous flow liquid handling system has been fabricated to increase throughput of the carrageenan PGP. Using the optimized parameters, the system can produce a volume of approximately 1700L/h.

MiR156-Targeted SBP-Box Transcription Factors Interact with DWARF53 to Regulate TEOSINTE BRANCHED1 and BARREN STALK1 Expression in Bread Wheat

Genetic and environmental factors affect bread wheat (Triticum aestivum) plant architecture, which determines grain yield. In this study, we demonstrate that miR156 controls bread wheat plant architecture. We show that overexpression of tae-miR156 in bread wheat cultivar Kenong199 leads to increased tiller number and severe defects in spikelet formation, probably due to the tae-miR156-mediated repression of a group of SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) genes. Furthermore, we found that the expression of two genes TEOSINTE BRANCHED1 (TaTB1) and BARREN STALK1 (TaBA1), whose orthologous genes in diverse plant species play conserved roles in regulating plant architecture, is markedly reduced in the tae-miR156-OE bread wheat plants. Significantly, we demonstrate that the strigolactone (SL) signaling repressor DWARF53 (TaD53), which physically associates with the transcriptional corepressor TOPLESS, can directly interact with the N-terminal domains of miR156-controlled TaSPL3/17. Most importantly, TaSPL3/17-mediated transcriptional activation of TaBA1 and TaTB1 can be largely repressed by TaD53 in the transient expression system. Our results reveal potential association between miR156-TaSPLs and SL signaling pathways during bread wheat tillering and spikelet development.

Influence of silicon on growth, yield, and lodging resistance of MR219, a lowland rice of Malaysia

ABSTRACTLodging has limited yield and potential of increasing yield in rice. Lodging could be minimized by increasing the mechanical or physical strength of the rice culm. Silicon (Si) is associated with sturdiness and rigidity. Therefore, the objectives of this experiment were to evaluate the effects and optimum rate of Si application to improve yield, growth, and lodging resistance of MR219, a popular rice variety in Malaysia. Si, in the form of fertilizer, was applied at the onset of reproductive stage as topdressing. All Si-treated plants showed an increase in number of tillers, number of spikelets per panicle, number of effective tillers, percentage of filled spikelets, and weight per panicle in Si-treated plants as compared to control. Lodging resistance was higher in plants treated with Si as shown by bending parameters. Si-treated plants showed significant increase in flag leaf area, chlorophyll content, and Si content.

Drought-tolerant QTL qVDT11 leads to stable tiller formation under drought stress conditions in rice

Drought is an important limiting factor for rice production, but the genetic mechanisms of drought tolerance is poorly understood. Here, we screened 218 rice varieties to identify 32 drought-tolerant varieties. The variety Samgang exhibited strong drought tolerance and stable yield in rain-fed conditions and was selected for further study. To identify QTLs for drought tolerance, we examined visual drought tolerance (VDT) and relative water content (RWC) phenotypes in a doubled haploid (DH) population of 101 individuals derived from a cross between Samgang and Nagdong (a drought-sensitive variety). Three QTLs from Samgang were identified for VDT and explained 41.8% of the phenotypic variance. In particular, qVDT11 contributed 20.3% of the phenotypic variance for RWC. To determine QTL effects on drought tolerance in rain-fed paddy conditions, seven DH lines were selected according to the number of QTLs they contained. Of the drought-tolerance-associated QTLs, qVDT2 and qVDT6 did not affect tiller formation, but qVDT11 increased tiller number. Tiller formation was most stable when qVDT2 and qVDT11 were combined. DH lines with both of these drought-tolerance-associated QTLs exhibited the most stable tiller formation. Together, these results suggest that qVDT11 is important for drought tolerance and stable tiller formation in rain-fed paddy fields.

No selection for greater size in an introduced grass invading semiarid grassland

Exotic species are often planted for restoration or to enhance production. Populations that expand from plantings may undergo selection in directions that differ from those produced by artificial selection prior to planting. Here, we test whether a highly productive grass, Agropyron cristatum (L.) Gaertn., introduced to the semiarid Great Plains of North America, evolves during invasion from seeded fields into native grassland. We grew individuals of A. cristatum from six seeded populations and 12 invading populations in 12 common gardens separated by 0.5–12 km for two growing seasons. Contrary to expectations, individuals from invading populations did not have significantly greater tiller number or growth (increase in tiller number) than did individuals from seeded populations, suggesting that they have not undergone evolution towards increased invasion ability through increased size or growth. Instead, there was a general trend for individuals from invading populations to have lower growth rates and fewer tillers when grown without neighbours. Large size or high growth rates arising from artificial selection prior to introduction may be disadvantageous to populations invading semiarid grassland on dry, nutrient-poor soils. In this case, evolution may have resulted in convergence between the relatively large planted species and the smaller native species.

Rice Dwarf Virus P2 Protein Hijacks Auxin Signaling by Directly Targeting the Rice OsIAA10 Protein, Enhancing Viral Infection and Disease Development.

The phytohormone auxin plays critical roles in regulating myriads of plant growth and developmental processes. Microbe infection can disturb auxin signaling resulting in defects in these processes, but the underlying mechanisms are poorly understood. Auxin signaling begins with perception of auxin by a transient co-receptor complex consisting of an F-box transport inhibitor response 1/auxin signaling F-box (TIR1/AFB) protein and an auxin/indole-3-acetic acid (Aux/IAA) protein. Auxin binding to the co-receptor triggers ubiquitination and 26S proteasome degradation of the Aux/IAA proteins, leading to subsequent events, including expression of auxin-responsive genes. Here we report that Rice dwarf virus (RDV), a devastating pathogen of rice, causes disease symptoms including dwarfing, increased tiller number and short crown roots in infected rice as a result of reduced sensitivity to auxin signaling. The RDV capsid protein P2 binds OsIAA10, blocking the interaction between OsIAA10 and OsTIR1 and inhibiting 26S proteasome-mediated OsIAA10 degradation. Transgenic rice plants overexpressing wild-type or a dominant-negative (degradation-resistant) mutant of OsIAA10 phenocopy RDV symptoms are more susceptible to RDV infection; however, knockdown of OsIAA10 enhances the resistance of rice to RDV infection. Our findings reveal a previously unknown mechanism of viral protein reprogramming of a key step in auxin signaling initiation that enhances viral infection and pathogenesis.

Canopy Architecture and Leaf Nitrogen Distribution of Rice (Oryza sativa L.) under Chronic Soil Water Deficit

AbstractThe development of vertical gradients of specific leaf nitrogen (SLN) in accordance with light gradients within a canopy is important for maximising resource‐use efficiency. In this study, we aimed to clarify the effect of chronic soil water deficit on the SLN gradient in rice. In a series of field experiments, SLN gradients of an indica cultivar and a tropical japonica cultivar were investigated under chronic soil water deficit. As a result, SLN gradient of an indica cultivar tended to be more uniform than that of a tropical japonica cultivar during the recovery period after dry spells under aerobic conditions: an indica cultivar distributed much N in shaded leaves while a japonica cultivar enhanced the SLN in the upper layers. We conclude that vertical gradient of SLN of indica cultivars becomes less optimal for photo‐assimilation under chronic soil water deficit, although they can take‐up sufficient amounts of N. This would be attributable to the rapid increase in tiller number upon rainfall or irrigation and prolonged tillering period for their recovery growth, leading to a more compact canopy architecture. The tillering habit in the current indica irrigated rice cultivars would be associated with the response of SLN gradients to chronic soil water deficit.

Down-Regulation of Cytokinin Oxidase 2 Expression Increases Tiller Number and Improves Rice Yield.

BackgroundCytokinins are plant-specific hormones that affect plant growth and development. The endogenous level of cytokinins in plant cells is regulated in part by irreversible degradation via cytokinin oxidase/dehydrogenase (CKX). Among the 11 rice CKXs, CKX2 has been implicated in regulation of rice grain yield.ResultsTo specifically down-regulate OsCKX2 expression, we have chosen two conserved glycosylation regions of OsCKX2 for designing artificial short hairpin RNA interference genes (shRNA-CX3 and -CX5, representing the 5′ and 3′ glycosylation region sequences, respectively) for transformation by the Agrobacterium-mediated method. For each construct, 5 independent transgenic lines were obtained for detailed analysis. Southern blot analysis confirmed the integration of the shRNA genes into the rice genome, and quantitative real time RT-PCR and northern blot analyses showed reduced OsCKX2 expression in the young stem of transgenic rice at varying degrees. However, the expression of other rice CKX genes, such as CKX1 and CKX3, in these transgenic lines was not altered. Transgenic rice plants grown in the greenhouse were greener and more vigorous with delayed senescence, compared to the wild type. In field experiments, both CX3 and CX5 transgenic rice plants produced more tillers (27–81 %) and grains (24–67 %) per plant and had a heavier 1000 grain weight (5–15 %) than the wild type. The increases in grain yield were highly correlated with increased tiller numbers. Consistently, insertional activation of OsCKX2 led to increased expression of CKX2 and reduced tiller number and growth in a gene-dosage dependant manner.ConclusionsTaken together, these results demonstrate that specific suppression of OsCKX2 expression through shRNA-mediated gene silencing leads to enhanced growth and productivity in rice by increasing tiller number and grain weight.Electronic supplementary materialThe online version of this article (doi:10.1186/s12284-015-0070-5) contains supplementary material, which is available to authorized users.

Constitutive Expression of Rice MicroRNA528 Alters Plant Development and Enhances Tolerance to Salinity Stress and Nitrogen Starvation in Creeping Bentgrass.

MicroRNA528 (miR528) is a conserved monocot-specific small RNA that has the potential of mediating multiple stress responses. So far, however, experimental functional studies of miR528 are lacking. Here, we report that overexpression of a rice (Oryza sativa) miR528 (Osa-miR528) in transgenic creeping bentgrass (Agrostis stolonifera) alters plant development and improves plant salt stress and nitrogen (N) deficiency tolerance. Morphologically, miR528-overexpressing transgenic plants display shortened internodes, increased tiller number, and upright growth. Improved salt stress resistance is associated with increased water retention, cell membrane integrity, chlorophyll content, capacity for maintaining potassium homeostasis, CATALASE activity, and reduced ASCORBIC ACID OXIDASE (AAO) activity; while enhanced tolerance to N deficiency is associated with increased biomass, total N accumulation and chlorophyll synthesis, nitrite reductase activity, and reduced AAO activity. In addition, AsAAO and COPPER ION BINDING PROTEIN1 are identified as two putative targets of miR528 in creeping bentgrass. Both of them respond to salinity and N starvation and are significantly down-regulated in miR528-overexpressing transgenics. Our data establish a key role that miR528 plays in modulating plant growth and development and in the plant response to salinity and N deficiency and indicate the potential of manipulating miR528 in improving plant abiotic stress resistance.

Characterization and mapping of d13, a dwarfing mutant gene, in rice

Plant height is one of the most important agronomic traits in crop breeding because dwarf and semi-dwarf cultivars are resistant to lodging and have led to remarkable yield increases in cereal crops. Although several genes related to gibberellins signaling or biosynthesis resulting in dwarfism have been isolated, however, lots of causal genes controlling dwarfism remain to be uncovered. We characterized a dwarf mutant (ID13) in rice. The mutant displayed several altered phenotypes compared to the wild type, such as reduced plant height, increased tiller number, short and rounded leaf tips, presence of a yellowish stripe on the leaf blade, late and asynchronous heading, strong root systems, short erect panicle, smaller seed size, etc. The dwarfism of the mutant was responsive to gibberellic acid (GA), based on the analyses of two GA-mediated processes. Anatomical observations revealed that the mutant plants had fewer vascular bundles and reduced cell size compared with wild type plants. Genetic analysis indicated that the dwarf mutant was controlled by a single recessive gene, d13, which was flanked by two STS markers, DMR-3 and S5789, within the physical distance of 265 kb around the centromeric region on chromosome 9. Cloning and functional analysis is in progress.

The effect of chronic gamma ray irradiation on lignocellulose of Brachypodium distachyon

The effects of chronic gamma ray irradiation on Brachypodium distachyon were investigated to lignocellulose composition and enzymatic hydrolysis. Four-week-old plants of B. distachyon were exposed to gamma-ray irradiation at doses of 50, 100, 150, 200, 250, and 300 Gy. Gamma-ray irradiation negatively influenced biomass related morphology including plant height and cell size; however, it increased tiller number and internode diameter. SEM image analysis showed that the cell size of 300-Gy gamma irradiated plants was 45 % lower than that of the control. Destroyed regions on the cell wall surface were observed according to the dose of radiation. Cell wall yield, lignin content, and neutral sugar content were decreased in a dose-dependent manner. Glucose yield via enzymatic hydrolysis was positively correlated with radiation dose. In addition, 250-Gy and 300-Gy irradiated plants showed significantly better saccharification efficiency than non-irradiated controls. Initial glucose yields from 250-Gy- and 300-Gy-irradiated plants were 121.5 and 139.4 % of yields from non-irradiated controls, and final yields were 184.7 and 213.7 % of control yields, respectively. Reverse-transcription polymerase chain reaction (RT-PCR) analysis of lignin pathway-related genes showed increase of F5H, COMT, and CAD expression in 250-Gy- and 300-Gy-irradiated Brachypodium plants. Chemical composition analysis further verified that chronic gamma ray irradiation degraded lignocellulose as a pretreatment.

Regulation of OsmiR156h through Alternative Polyadenylation Improves Grain Yield in Rice.

Substantial increases in grain yield of cereal crops are required to feed a growing human population. Here we show that a natural variant of SEMIDWARF AND HIGH-TILLERING (SDT) increases harvest index and grain productivity in rice. Gain-of-function sdt mutation has a shortened polyadenylation tail on the OsmiR156h microRNA precursor, which cause the up-regulation of OsmiR156h. The plants carrying the semidominant sdt allele exhibit reduced plant height, enhanced lodging resistance, increased tiller numbers per plant, and resulting in an increased grain yield. We also show that combining the sdt allele with the OsSPL14WFP allele can be effective in simultaneously improving tillering capacity and panicle branching, thereby leading to higher harvest index and grain yield. Most importantly, pyramiding of the sdt allele and the green revolution gene sd1 enhances grain yield by about 20% in hybrid rice breeding. Our results suggest that the manipulation of the polyadenylation status of OsmiR156 represents a novel strategy for improving the yield potential of rice over what is currently achievable.

Halotolerant rhizobacteria: beneficial plant metabolites and growth enhancement of Triticum aestivum L. in salt-amended soils

Salt-tolerant strains of Enterobacter asburiae, Bacillus thuringiensis, Moraxella pluranimalium and Pseudomonas stutzeri were evaluated for their ability to alleviate salt stress of wheat (Triticum aestivum L.) seedlings. 1-Aminocyclopropane-1-carboxylate deaminase activity of P. stutzeri S-80 and B. thuringiensis S-26 was 190 and 183 nmol h−1, respectively. Maximum levels of auxin were recorded with P. stutzeri S-80 (107 µg ml−1) and E. asburiae S-24 (143 µg ml−1) under normal and salt-stressed conditions (0.25M NaCl), respectively, with 500 µg ml−1 L-tryptophan. Auxin response mediated by rhizobacteria was also demonstrated by microscopically assaying the transgenic auxin-responsive reporter DR5::GUS expression tomato (Solanum lycopersicum L. cv. MicroTom). In pot trials, seedlings fresh and dry biomass witnessed highly significant improvements of 1- and 2.2-folds, respectively, with M. pluranimalium S-29 (at 100 mM NaCl) and E. asburiae S-24 (150 mM NaCl), over control. At final harvest, maximum increase in number of tillers (up to 94%) and seed weight (up to 40%) was recorded with E. asburiae S-24 and M. pluranimalium S-29 at 200 mM salt stress. In conclusion, newly isolated strains of M. pluranimalium S-29, E. asburiae S-24 and P. stutzeri S-80 enhanced the growth of T. aestivum by mitigating the salt stress of plants.

Alteration of osa-miR156e expression affects rice plant architecture and strigolactones (SLs) pathway.

Overexpressing osa--miR156e in rice produced a bushy mutant and osa--miR156e regulation of tillering may do this through the strigolactones (SLs) pathway. Appropriate downregulation of osa--miR156 expression contributed to the improvement of plant architecture. Tillering is one of the main determinants for rice architecture and yield. In this study, a bushy mutant of rice was identified with increased tiller number, reduced plant height, prolonged heading date, low seed setting, and small panicle size due to a T-DNA insertion which essentially elevated the expression of osa-miR156e. Transgenic plants with constitutive expression of osa-miR156e also had the bushy phenotype, which showed osa-miR156 may control apical dominance and tiller outgrowth via regulating the strigolactones signaling pathway. Furthermore, the extent of impaired morphology was correlated with the expression level of osa-miR156e. In an attempt to genetically improve rice architecture, ectopic expression of osa-miR156e under the GAL4-UAS system or OsTB1 promoter was conducted. According to agronomic trait analysis, pTB1:osa-miR156e transgenic plants significantly improved the grain yield per plant compared to plants overexpressing osa-miR156e, even though the yield was still inferior to the wild type, making it a very interesting albeit negative result. Our results suggested that osa-miR156 could serve as a potential tool for modifying rice plant architecture through genetic manipulation of the osa-miR156 expression level.

Morphological traits associated with vegetative growth of rice (Oryzasativa L.) during the recovery phase after early-season drought

Rapid leaf growth during the recovery period after a dry spell is essential for the adaptation of rice (Oryza sativa L.) to drought–prone environments. However, how rice plants resume growth when the drought stress ends is not well understood. The objective of this study was to determine the traits and mechanisms associated with the above-ground morphological response to rewatering after early-season drought, by comparing three rice lines with contrastive plant architectures. In the field, we measured the above-ground architecture, carbohydrate partitioning, and consumption of non-structural carbohydrates by IR64 (indica rice), a New Plant Type line (tropical japonica rice) and an IR64 introgression line (IL) with large leaves and reduced tillering under fully irrigated and drought+rewatered conditions. In an ancillary pot experiment, we monitored changes in tiller number and leaf growth under fully irrigated, droughted and drought+rewatered conditions. There were genotypic differences in recovery growth patterns upon rewatering after drought: the New Plant Type lines prioritized individual tiller growth, while IR64 and the IR64 IL prioritized the production of new tillers and concomitantly consumed much carbohydrate. The increase in tiller number during the recovery period was lower in the IR64 IL than in IR64 owing to the longer phyllochron and larger amount of assimilate required to produce new tillers in the IL. Rice development during the recovery period depends on the plant type (constitutive tiller number to size ratio) and tillering response to soil moisture regime, which would be mediated mainly by phyllochron and tiller production per assimilate. Rapid increase in tiller number upon rewatering in IR64 was associated with the low amount of assimilate required to produce new tillers rather than with the short phyllochron.