The miRNA-mRNA Networks Involving Abnormal Energy and Hormone Metabolisms Restrict Tillering in a Wheat Mutant dmc

Strigolactone and abscisic acid synthesis and signaling pathways are enhanced in the wheat oligo-tillering mutant ot1

Tiller number greatly contributes to grain yield in wheat. Using ethylmethanesulfonate mutagenesis, we previously discovered the oligo-tillering mutant ot1. The tiller number was significantly lower in ot1 than in the corresponding wild type from the early tillering stage until the heading stage. Compared to the wild type, the thousand-grain weight and grain length were increased by 15.41% and 31.44%, respectively, whereas the plant height and spike length were decreased by 26.13% and 37.25%, respectively. Transcriptomic analysis was conducted at the regreening and jointing stages to identify differential expressed genes (DEGs). Functional enrichment analysis with the Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) databases showed differential expression of genes associated with ADP binding, transmembrane transport, and transcriptional regulation during tiller development. Differences in tiller number in ot1 led to the upregulation of genes in the strigolactone (SL) and abscisic acid (ABA) pathways. Specifically, the SL biosynthesis genes DWARF (D27), D17, D10, and MORE AXILLARY GROWTH 1 (MAX1) were upregulated by 3.37- to 8.23-fold; the SL signal transduction genes D14 and D53 were upregulated by 1.81- and 1.32-fold, respectively; the ABA biosynthesis genes 9-CIS-EPOXICAROTENOID DIOXIGENASE 3 (NCED3) and NCED5 were upregulated by 1.66- and 3.4-fold, respectively; and SNF1-REGULATED PROTEIN KINASE2 (SnRK2) and PROTEIN PHOSPHATASE 2C (PP2C) genes were upregulated by 1.30- to 4.79-fold. This suggested that the tiller number reduction in ot1 was due to alterations in plant hormone pathways. Genes known to promote tillering growth were upregulated, whereas those known to inhibit tillering growth were downregulated. For example, PIN-FORMED 9 (PIN9), which promotes tiller development, was upregulated by 8.23-fold in ot1; Ideal Plant Architecture 1 (IPA1), which inhibits tiller development, was downregulated by 1.74-fold. There were no significant differences in the expression levels of TILLER NUMBER 1 (TN1) or TEOSINTE BRANCHED 1 (TB1), indicating that the tiller reduction in ot1 was not controlled by known genes. Our findings provide valuable data for subsequent research into the genetic bases and regulatory mechanisms of wheat tillering.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-024-01450-3.

Wheat gibberellin oxidase genes and their functions in regulating tillering

Multiple genetic factors control tillering, a key agronomy trait for wheat (Triticum aestivum L.) yield. Previously, we reported a dwarf-monoculm mutant (dmc) derived from wheat cultivar Guomai 301, and found that the contents of gibberellic acid 3 (GA3) in the tiller primordia of dmc were significantly higher. Transcriptome analysis indicated that some wheat gibberellin oxidase (TaGAox) genes TaGA20ox-A2, TaGA20ox-B2, TaGA3ox-A2, TaGA20ox-A4, TaGA2ox-A10 and TaGA2ox-B10 were differentially expressed in dmc. Therefore, this study systematically analyzed the roles of gibberellin oxidase genes during wheat tillering. A total of 63 TaGAox genes were identified by whole genome analysis. The TaGAoxs were clustered to four subfamilies, GA20oxs, GA2oxs, GA3oxs and GA7oxs, including seven subgroups based on their protein structures. The promoter regions of TaGAox genes contain a large number of cis-acting elements closely related to hormone, plant growth and development, light, and abiotic stress responses. Segmental duplication events played a major role in TaGAoxs expansion. Compared to Arabidopsis, the gene collinearity degrees of the GAoxs were significantly higher among wheat, rice and maize. TaGAox genes showed tissue-specific expression patterns. The expressions of TaGAox genes (TaGA20ox-B2, TaGA7ox-A1, TaGA2ox10 and TaGA3ox-A2) were significantly affected by exogenous GA3 applications, which also significantly promoted tillering of Guomai 301, but didn't promote dmc. TaGA7ox-A1 overexpression transgenic wheat lines were obtained by Agrobacterium mediated transformation. Genomic PCR and first-generation sequencing demonstrated that the gene was integrated into the wheat genome. Association analysis of TaGA7ox-A1 expression level and tiller number per plant demonstrated that the tillering capacities of some TaGA7ox-A1 transgenic lines were increased. These data demonstrated that some TaGAoxs as well as GA signaling were involved in regulating wheat tillering, but the GA signaling pathway was disturbed in dmc. This study provided valuable clues for functional characterization of GAox genes in wheat.

Identification and high-resolution mapping of a novel tiller number gene (tin6) by combining forward genetics screen and MutMap approach in bread wheat

Wheat (Triticum aestivum) is one of the most important food crops worldwide, providing up to 20% of the caloric intake per day. Developing high-yielding wheat cultivars with tolerance against abiotic and biotic stresses is important to keep up with the increasing human population. Tiller number is one of the major yield-related traits, directly affecting the number of grains produced per plant; however, only a small number of QTL and underlining genes have been identified for this important factor. Identification of novel genetic variation underlying contrasting traits and their precise genetic mapping in wheat is considered difficult due to the complexity and size of the genome; however, advancements in genomic resources have made efficient gene localization more possible. In this study, we report the characterization of a novel tillering number gene using a mutant identified in the forward genetic screen of an ethyl methane sulfonate (EMS)-treated population of cv. "Jagger." By crossing the low tillering mutant with the Jagger wild-type plant, we generated an F2 population and used the MutMap approach to identify a novel physical interval on 11 Mb on chromosome 2DS. Using an F₂ population of 442 gametes and polymorphic SNP markers, we were able to delineate the tin6 locus to a 2.1 Mb region containing 22 candidate genes.

Fine mapping of a stripe rust resistance gene YrZM175 in bread wheat

A stripe rust resistance gene YrZM175 in Chinese wheat cultivar Zhongmai 175 was mapped to a genomic interval of 636.4 kb on chromosome arm 2AL, and a candidate gene was predicted. Stripe rust, caused by Puccinia striiformis f. sp. tritici (PST), is a worldwide wheat disease that causes large losses in production. Fine mapping and cloning of resistance genes are important for accurate marker-assisted breeding. Here, we report the fine mapping and candidate gene analysis of stripe rust resistance gene YrZM175 in a Chinese wheat cultivar Zhongmai 175. Fifteen F₁, 7,325 F₂ plants and 117 F_2:3 lines derived from cross Avocet S/Zhongmai 175 were inoculated with PST race CYR32 at the seedling stage in a greenhouse, and F_2:3 lines were also evaluated for stripe rust reaction in the field using mixed PST races. Bulked segregant RNA-seq (BSR-seq) analyses revealed 13 SNPs in the region 762.50-768.52 Mb on chromosome arm 2AL. By genome mining, we identified SNPs and InDels between the parents and contrasting bulks and mapped YrZM175 to a 0.72-cM, 636.4-kb interval spanned by YrZM175-InD1 and YrZM175-InD2 (763,452,916-764,089,317 bp) including two putative disease resistance genes based on IWGSC RefSeq v1.0. Collinearity analysis indicated similar target genomic intervals in Chinese Spring, Aegilops tauschii (2D: 647.7-650.5 Mb), Triticum urartu (2A: 750.7-752.3 Mb), Triticum dicoccoides (2A: 771.0-774.5 Mb), Triticum turgidum (2B: 784.7-788.2 Mb), and Triticum aestivum cv. Aikang 58 (2A: 776.3-778.9 Mb) and Jagger (2A: 789.3-791.7 Mb). Through collinearity analysis, sequence alignments of resistant and susceptible parents and gene expression level analysis, we predicted TRITD2Bv1G264480 from Triticum turgidum to be a candidate gene for map-based cloning of YrZM175. A gene-specific marker for TRITD2Bv1G264480 co-segregated with the resistance gene. Molecular marker analysis and stripe rust response data revealed that YrZM175 was different from genes Yr1, Yr17, Yr32, and YrJ22 located on chromosome 2A. Fine mapping of YrZM175 lays a solid foundation for functional gene analysis and marker-assisted selection for improved stripe rust resistance in wheat.

Fine mapping of the tiller inhibition gene TIN4 contributing to ideal plant architecture in common wheat

A tiller inhibition gene, TIN4, was mapped to an approximately 311 kb genomic interval on chromosome arm 2DL of wheat. The tiller is one of the key components of plant morphological architecture and a central agronomic trait affecting spike number in wheat. Low tiller number has been proposed as a major component of crop ideotypes for high yield potential. In this study, we characterized the development of tillering in near-isogenic lines (NIL7A and NIL7B), indicating that the TIN4 gene inhibited the growth of tillering buds and negatively regulated tiller number. Low-tillering was controlled by a single gene (TIN4) located on chromosome 2DL by genetic analysis and bulked segregant RNA-seq analysis. A total of 17 new polymorphic markers were developed in this study, and 61 recombinants were identified in the secondary F2 population containing 4,266 individuals. TIN4 was finally mapped on a 0.35 cM interval, co-segregated with molecular marker M380, within a 311 kb genomic interval of the wheat cultivar Chinese Spring reference genome sequence that contained twelve predicted genes. Yield experiments showed that the yield of low-tillering lines was higher than that of high-tillering lines at a higher density. Overall, this study provides a foundation for the construction of a low-tillering ideotype for improving wheat yield and further cloning TIN4 by map-based cloning approach.

Key auxin response factor (ARF) genes constraining wheat tillering of mutant dmc

Tillering ability is a key agronomy trait for wheat (Triticum aestivum L.) production. Studies on a dwarf monoculm wheat mutant (dmc) showed that ARF11 played an important role in tillering of wheat. In this study, a total of 67 ARF family members were identified and clustered to two main classes with four subgroups based on their protein structures. The promoter regions of T. aestivum ARF (TaARF) genes contain a large number of cis-acting elements closely related to plant growth and development, and hormone response. The segmental duplication events occurred commonly and played a major role in the expansion of TaARFs. The gene collinearity degrees of the ARFs between wheat and other grasses, rice and maize, were significantly high. The evolution distances among TaARFs determine their expression profiles, such as homoeologous genes have similar expression profiles, like TaARF4-3A-1, TaARF4-3A-2 and their homoeologous genes. The expression profiles of TaARFs in various tissues or organs indicated TaARF3, TaARF4, TaARF9 and TaARF22 and their homoeologous genes played basic roles during wheat development. TaARF4, TaARF9, TaARF12, TaARF15, TaARF17, TaARF21, TaARF25 and their homoeologous genes probably played basic roles in tiller development. qRT-PCR analyses of 20 representative TaARF genes revealed that the abnormal expressions of TaARF11 and TaARF14 were major causes constraining the tillering of dmc. Indole-3-acetic acid (IAA) contents in dmc were significantly less than that in Guomai 301 at key tillering stages. Exogenous IAA application significantly promoted wheat tillering, and affected the transcriptions of TaARFs. These data suggested that TaARFs as well as IAA signaling were involved in controlling wheat tillering. This study provided valuable clues for functional characterization of ARFs in wheat.

MiR319-targeted OsTCP21 and OsGAmyb regulate tillering and grain yield in rice

Multiple genes and microRNAs (miRNAs) improve grain yield by promoting tillering. MiR319s are known to regulate several aspects of plant development; however, whether miR319s are essential for tillering regulation remains unclear. Here, we report that miR319 is highly expressed in the basal part of rice plant at different development stages. The miR319 knockdown line Short Tandem Target Mimic 319 (STTM319) showed higher tiller bud length in seedlings under low nitrogen (N) condition and higher tiller bud number under high N condition compared with the miR319a-overexpression line. Through targets prediction, we identified OsTCP21 and OsGAmyb as downstream targets of miR319. Moreover, OsTCP21 and OsGAmyb overexpression lines and STTM319 had increased tiller bud length and biomass, whereas both were decreased in OsTCP21 and OsGAmyb knockout lines and OE319a. These data suggest that miR319 regulates rice tiller bud development and tillering through targeting OsTCP21 and OsGAmyb. Notably, the tiller number and grain yield increased in STTM319 and overexpression lines of OsTCP21 and OsGAmyb but decreased in OE319a and knockout lines of OsTCP21 and OsGAmyb. Taken together, our findings indicate that miR319s negatively affect tiller number and grain yield by targeting OsTCP21 and OsGAmyb, revealing a novel function for miR319 in rice.

Key wheat GRF genes constraining wheat tillering of mutant dmc

Tillering is a key agronomy trait for wheat (Triticum aestivum L.) production. Previously, we have reported a dwarf-monoculm wheat mutant (dmc) obtained from cultivar Guomai 301 (wild type, WT), and found growth regulating factors (GRFs) playing important roles in regulating wheat tillering. This study is to systematically investigate the roles of all the wheat GRFs (T. aestivum GRFs, TaGRFs) in regulating tillering, and screen out the key regulators. A total of 30 TaGRFs were identified and their physicochemical properties, gene structures, conserved domains, phylogenetic relationships and tissue expression profiles were analyzed. The expression levels of all the TaGRFs were significantly lower in dmc than those in WT at early tillering stage, and the abnormal expressions of TaGRF2-7(A, B, D), TaGRF5-7D, TaGRF10-6(A, B, D) and TaGRF11-2A were major causes constraining the tillering of dmc. The transcriptions of TaGRFs were significantly affected by exogenous indole acetic acid (IAA) and gibberellin acid (GA3) applications, which suggested that TaGRFs as well as IAA, GA signaling were involved in controlling wheat tillering. This study provided valuable clues for functional characterization of GRF genes in wheat.

Regulation of Aegilops tauschii Coss Tiller Bud Growth by Plant Density: Transcriptomic, Physiological and Phytohormonal Responses

Aegilops tauschii Coss is one of the most hazardous weeds that severely infests wheat fields in China. The tillering ability of Ae. tauschii strongly affects the occurrence and spread by influencing its seed output. In this study, Ae. tauschii was sown at low plant density (LPD) and high plant density (HPD) to investigate the effect of plant density on tiller bud outgrowth and its potential regulators using RNA-Seq. Additionally, the chlorophyll content and photosynthesis, soluble sugar and phytohormone levels were also determined at different plant densities. The results showed that an increased plant density significantly inhibited the elongation of tiller buds in the axil of the first leaf at 15 days after planting, with 7.69 mm at LPD and 1.69 mm at HPD. A total of seven putative tiller-related genes were selected and validated using quantitative real-time PCR. Furthermore, chlorophyll levels, photosynthetic efficiency, and soluble sugar contents were distinctly inhibited by HPD in Ae. tauschii, which may be responsible for the restriction of tiller bud growth. In addition, differentially expressed genes (DEGs) were markedly enriched in indole-3-acetic acid (IAA), abscisic acid (ABA), and gibberellin metabolism and signaling. Accordingly, the levels of ABA and gibberellin A3 in Ae. tauschii were strikingly higher at HPD compared with those at LPD, yet the reverse tendency was observed for IAA. Undoubtedly, such results will be highly beneficial for illuminating the underlying regulators of the Ae. tauschii tillering response to plant density and may provide new ideas for the control of this weed in the future.