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The objective was to evaluate the tillering pattern in the period before and during the stockpiling of the marandu, mavuno, ipyporã and mulato II cultivars. The experimental design was completely randomized, with four replications. The tiller appearance rate (TAR) showed a similar pattern among grasses, being higher in the previous and initial stockpiling period. Among the forages, the ipyporã grass showed the highest TAR in the pre-stockpiling period. The tiller mortality rate was higher at the end of the stockpiling period. The balance between tiller appearance and mortality rates (BAL) was positive in the previous and initial stockpiling period and negative in the intermediate and final phases of stockpiling period. The BAL of the ipyporã grass was superior in the pre-stockpiling, in relation to the other grasses. The stability index showed a response pattern similar to the BAL. The number of tillers was higher in the middle, intermediate in the beginning and end, but lower in the pre-stockpiling period. The ipyporã grass has later regrowth vigor in the pre- stockpiling period. Population stability of tillers of the marandu, mavuno, ipyporã and mulato II grasses is not compromised during the stockpiling.

Manual phenotyping of rice tillers is time consuming and labor intensive, and lags behind the rapid development of rice functional genomics. Thus, automated, non-destructive methods of phenotyping rice tiller traits at a high spatial resolution and high throughput for large-scale assessment of rice accessions are urgently needed. In this study, we developed a high-throughput micro-CT-RGB imaging system to non-destructively extract 739 traits from 234 rice accessions at nine time points. We could explain 30% of the grain yield variance from two tiller traits assessed in the early growth stages. A total of 402 significantly associated loci were identified by genome-wide association study, and dynamic and static genetic components were found across the nine time points. A major locus associated with tiller angle was detected at time point 9, which contained a major gene, TAC1. Significant variants associated with tiller angle were enriched in the 3ʹ-untranslated region of TAC1. Three haplotypes for the gene were found, and rice accessions containing haplotype H3 displayed much smaller tiller angles. Further, we found two loci containing associations with both vigor-related traits identified by high-throughput micro-CT-RGB imaging and yield. The superior alleles would be beneficial for breeding for high yield and dense planting.

Summary Amino acid transporters (AATs) play indispensable roles in nutrient allocation during plant development. In this study, we demonstrated that inhibiting expression of the rice amino acid transporter OsAAP3 increased grain yield due to a formation of larger numbers of tillers as a result of increased bud outgrowth. Elevated expression of OsAAP3 in transgenic plants resulted in significantly higher amino acid concentrations of Lys, Arg, His, Asp, Ala, Gln, Gly, Thr and Tyr, and inhibited bud outgrowth and rice tillering. However, RNAi of OsAAP3 decreased significantly Arg, Lys, Asp and Thr concentrations to a small extent, and thus promoted bud outgrowth, increased significantly tiller numbers and effective panicle numbers per plant, and further enhanced significantly grain yield and nitrogen use efficiency (NUE). The promoter sequences of OsAAP3 showed some divergence between Japonica and Indica rice, and expression of the gene was higher in Japonica, which produced fewer tillers than Indica. We generated knockout lines of OsAAP3 on Japonica ZH11 and KY131 using CRISPR technology and found that grain yield could be increased significantly. These results suggest that manipulation of OsAAP3 expression could be used to increase grain yield in rice.

• The degree of rice tillering is an important agronomic trait that can be markedly affected by nitrogen supply. However, less is known about how nitrogen-regulated rice tillering is related to polar auxin transport. • Compared with nitrate, ammonium induced tiller development and was paralleled with increased ³H-indole-acetic acid (IAA) transport and greater auxin into the junctions. OsPIN9, an auxin efflux carrier, was selected as the candidate gene involved in ammonium-regulated tillering based on GeneChip data. • Compared with wild-type plants, ospin9 mutants had fewer tillers, and OsPIN9 overexpression increased the tiller number. Additionally, OsPIN9 was mainly expressed in vascular tissue of the junction and tiller buds, and encoded a membrane-localised protein. Heterologous expression in Xenopus oocytes and yeast demonstrated that OsPIN9 is a functional auxin efflux transporter. More importantly, its RNA and protein levels were induced by ammonium but not by nitrate, and tiller numbers in mutants did not respond to nitrogen forms. Further advantages, including increased tiller number and grain yield, were observed in overexpression lines grown in the paddy field at a low-nitrogen rate compared with at a high-nitrogen rate. • Our data revealed that ammonium supply and an auxin efflux transporter co-ordinately control tiller bud elongation in rice.

Summary Tillering is a significant agronomic trait in wheat which shapes plant architecture and yield. Strigolactones (SLs) function in inhibiting axillary bud outgrowth. The roles of SLs in the regulation of bud outgrowth have been described in model plant species, including rice and Arabidopsis. However, the role of SLs genes in wheat remains elusive due to the size and complexity of the wheat genomes. In this study, TaD27 genes in wheat, orthologs of rice D27 encoding an enzyme involved in SLs biosynthesis, were identified. TaD27‐RNAi wheat plants had more tillers, and TaD27‐B‐OE wheat plants had fewer tillers. Germination bioassay of Orobanche confirmed the SLs was deficient in TaD27‐RNAi and excessive in TaD27‐B‐OE wheat plants. Moreover, application of exogenous GR24 or TIS108 could mediate the axillary bud outgrowth of TaD27‐RNAi and TaD27‐B‐OE in the hydroponic culture, suggesting that TaD27‐B plays critical roles in regulating wheat tiller number by participating in SLs biosynthesis. Unlike rice D27, plant height was not affected in the transgenic wheat plants. Transcription and gene coexpression network analysis showed that a number of genes are involved in the SLs signalling pathway and axillary bud development. Our results indicate that TaD27‐B is a key factor in the regulation of tiller number in wheat.

• Shoot branches are formed from the axillary meristem and their formation is a key process in plant development. Although our understanding of the mechanisms underlying stem cell maintenance in the shoot apical meristem (SAM) is progressing, our knowledge of these mechanisms during the process of axillary meristem development is insufficient. • To elucidate the genetic mechanisms underlying axillary meristem development in rice (Oryza sativa), we undertook a molecular genetic analysis focusing on TILLERS ABSENT1 (TAB1) and FLORAL ORGAN NUMBER2 (FON2), respective orthologs of the WUSCHEL and CLAVATA3 genes involved in SAM maintenance in Arabidopsis (Arabidopsis thaliana). • We revealed that stem cells were established at an early stage of axillary meristem development in the wild-type, but were not maintained in tab1. By contrast, the stem cell region and TAB1 expression domain were expanded in fon2, and FON2 overexpression inhibited axillary meristem formation. • These results indicate that TAB1 is required to maintain stem cells during axillary meristem development, whereas FON2 negatively regulates stem cell fate by restricting TAB1 expression. Thus, the genetic pathway regulating SAM maintenance in Arabidopsis seems to have been recruited to play a specific role within a narrow developmental window – namely, axillary meristem establishment – in rice.

The quantity and quality of tillers determine the yield of rice. In order to explore how optimized nitrogen fertilizer application (OFA) increases rice yield by affecting tiller growth, a pot experiment with three nitrogen treatments was performed on the basis of previous researches to investigate the growth and development of tillers. Results showed that under OFA, the emerging rate of secondary tillers and high leaf position tillers decreased, which increased with the number of primary tillers. The decrease of ineffective tillers increased the accumulation of biomass and nitrogen per tiller, which promoted the development of panicles. Compared with traditional nitrogen fertilizer application (TFA), the differentiated number of spikelets increased by 10.85%–21.70%, which led to the total number of filled spikelets increasing by 9.67%–18.95%, resulting in 9.6% increase in rice yield. Primary tillers, especially at the first, second, fifth, and sixth leaf positions, were the superior tillers in good quality, which made great contribution to rice yield and were significantly affected by nitrogen application. Making full use of the regulation effect of nitrogen on the quality of tillers will help to stabilize rice yield with less nitrogen input or increase rice yield without adding nitrogen input.

The increase in the number of tillers of rice significantly affects grain yield. However, this is measured only by the manual counting of emerging tillers, where the most common method is to count by hand touching. This study develops an efficient, non-destructive method for estimating the number of tillers during the vegetative and reproductive stages under flooded conditions. Unlike popular deep-learning-based approaches requiring training data and computational resources, we propose a simple image-processing pipeline following the empirical principles of synchronously emerging leaves and tillers in rice morphogenesis. Field images were taken by an unmanned aerial vehicle at a very low flying height for UAV imaging—1.5 to 3 m above the rice canopy. Subsequently, the proposed image-processing pipeline was used, which includes binarization, skeletonization, and leaf-tip detection, to count the number of long-growing leaves. The tiller number was estimated from the number of long-growing leaves. The estimated tiller number in a 1.1 m × 1.1 m area is significantly correlated with the actual number of tillers, with 60% of hills having an error of less than ±3 tillers. This study demonstrates the potential of the proposed image-sensing-based tiller-counting method to help agronomists with efficient, non-destructive field phenotyping.

BackgroundAmino acids, which are transported by amino acid transporters, are the major forms of organic nitrogen utilized by higher plants. Among the 19 Amino Acid Permease transporters (AAPs) in rice, only a small number of these genes have been reported to influence rice growth and development. However, whether other OsAAPs are responsible for rice growth and development is unclear.ResultsIn this study, we demonstrate that OsAAP4 promoter sequences are divergent between Indica and Japonica, with higher expression in the former, which produces more tillers and higher grain yield than does Japonica. Overexpression of two different splicing variants of OsAAP4 in Japonica ZH11 significantly increased rice tillering and grain yield as result of enhancing the neutral amino acid concentrations of Val, Pro, Thr and Leu. OsAAP4 RNA interference (RNAi) and mutant lines displayed opposite trends compared with overexpresing (OE) lines. In addition, exogenous Val or Pro at 0.5 mM significantly promoted the bud outgrowth of lines overexpressing an OsAAP4a splicing variant compared with ZH11, and exogenous Val or Pro at 2.0 mM significantly enhanced the bud outgrowth of lines overexpressing splicing variant OsAAP4b compared with ZH11. Of note, the results of a protoplast amino acid-uptake assay showed that Val or Pro at different concentrations was specifically transported and accumulated in these overexpressing lines. Transcriptome analysis further demonstrated that OsAAP4 may affect nitrogen transport and metabolism, and auxin, cytokinin signaling in regulating rice tillering.ConclusionOur results suggested that OsAAP4 contributes to rice tiller and grain yield by regulating neutral amino acid allocation through two different splicing variants and that OsAAP4 might have potential applications in rice breeding.

Summary Tiller angle is one of the most important agronomic traits and one key factor for wheat ideal plant architecture, which can both increase photosynthetic efficiency and greatly enhance grain yield. Here, a deacetylase HST1‐like (TaHST1L) gene controlling wheat tiller angle was identified by the combination of a genome‐wide association study (GWAS) and bulked segregant analysis (BSA). Ethyl methane sulfonate (EMS)‐mutagenized tetraploid wheat lines with the premature stop codon of TaHST1L exhibited significantly smaller tiller angles than the wild type. TaHST1L‐overexpressing (OE) plants exhibited significantly larger tiller angles and increased tiller numbers in both winter and spring wheat, while TaHST1L‐silenced RNAi plants displayed significantly smaller tiller angles and decreased tiller numbers. Moreover, TaHST1L strongly interacted with TaIAA17 and inhibited its expression at the protein level, and thus possibly improved the content of endogenous auxin in the basal tissue of tillers. The transcriptomics and metabolomics results indicated that TaHST1L might change plant architecture by mediating auxin signal transduction and regulating endogenous auxin levels. In addition, a 242‐bp insertion/deletion (InDel) in the TaHST1L‐A1 promoter altered transcriptional activity and TaHST1L‐A1b allele with the 242‐bp insertion widened the tiller angle of TaHST1L‐OE transgenic rice plants. Wheat varieties with TaHST1L‐A1b allele possessed the increased tiller angle and grain yield. Further analysis in wheat and its progenitors indicated that the 242‐bp InDel possibly originated from wild emmer and was strongly domesticated in the current varieties. Therefore, TaHST1L involved in the auxin signalling pathway showed the big potential to improve wheat yield by controlling plant architecture. TaHST1L interacting with TaIAA17 controls wheat tiller angle to affect grain yield through regulating endogenous auxin.