We identified DWARF TILLER1, aWUSCHEL-related homeobox (WOX) transcription factor, as a positive regulator of tiller growth. Most dwt1 mutant plants show normal main shoot but dwarf tillers and reduced panicle size. Tiller growth in dwt1 appears to be inhibited by the main shoot, as removal of the main shoot releases the first tiller. The non-elongating internodes in dwt1 show reduced cell number and cell size, while DWT1 was mainly expressed in the panicles but not internodes, suggesting that DWT1 plays a long distance regulatory role in promoting internode elongation. Genome-wide expression analysis revealed that the expression of genes related to cell division and elongation, as well as to homeostasis and signaling of cytokinin and gibberellin were affected in dwt1 un-elongated internodes. This study reveals that a WOX transcription factor controls the growth uniformity of tillers and the main shoot in rice.
1、The dwt1 mutant displays a dominant main shoot
Unlike wild-type plants, all dwt1 tillers form shorter culm and smaller panicles (Fig. 1A), but most dwt1 main shoots exhibit similar height at maturity as the wild type (Fig. 1B, E). The degree of dwarfism varied among the tillers of the same dwt1 plant (Fig. 1 C). In addition, the short internodes appear twisted and distorted in the dwt1 mutant at the mature developmental stage (Fig. 1D). In contrast to the defective internode development, the dwt1 main shoot develops a larger and denser panicle compared with that of the wild type (Fig. 1F). These observations suggest that dwt1 has defects in growth uniformity between the main shoot and tillers, and its main shoot appears to be dominant compared to tillers. To determine whether the dwt1 phenotype is related to apical dominance, the main shoot and each tiller of dwt1 at the vegetative stage were separated and replanted individually in the paddy field. Each of the regenerated plants from the main shoot or tillers of dwt1 plants developed an architecture similar to dwt1 exhibiting dwarf tillers but a normal main shoot (Fig. 2A and B). Therefore we conclude that dwt1 mutant plants have a characteristic main shoot dominance, which can be partially released by removing the developed main shoot during vegetative growth.
2、dwt1 has defects in cell proliferation and cell elongation in tiller internodes
Rice internode elongation involves cell division followed by cell elongation. Because the un-elongated internodes in dwt1 mutants are dramatically shorter (0.460.2 cm, n= 30) compared with wild-type plants (14.161.0 cm, n= 30) (Fig. 3A and B), we performed longitudinal sections of the second internodes which display obvious defective elongation in the mutant. The results show that the cells in the wild type are slender and elongated, with a cell length of about 172.6636.2 mm (n= 30) (Fig. 3C and E). However, dwt1 cells in the shorter internodes appear flat with a longitudinal length of about 20.963.7 mm (n =30) (Fig. 3D and E). Furthermore, the dwt1 second un-elongated internode had a dramatic reduction in cell number per internode (247635, n= 5) in the longitudinal direction compared with the wild type (1077690, n =5) (Fig. 3F), suggesting that dwt1 has defects in both cell proliferation and cell elongation along the longitudinal direction in the tiller internodes.
3、DWT1 encodes a WOX transcription factor
Three annotated open reading frames in this region were sequenced, and a single base pair deletion was observed in one of the genes, LOC_Os01g47710 (Fig. 4B), which was predicted to encode a putative WUSCHEL-like homeobox (WOX) protein. Furthermore, the DWT1 protein fused with yellow fluorescent protein (YFP) is localized in the nucleus when transformed into tobacco leaves (Fig. 4E–H), consistent with the prediction of a transcription factor of WOX protein. Whether this sequence variation causes rice morphological difference between cultivated rice and wild rice remains to be elucidated.
4、DWT1 functions in a non-cell autonomous manner
Quantitative reverse transcription (qRT)-PCR analysis revealed the expression of DWT1 mRNA in the callus, young panicle, young embryo, root tip and coleoptile, but not in the mature leaves, and mature spikelets (Fig. 5A). A higher expression level of DWT1 was observed in panicles of tillers than that of the main shoot (Fig. 5B). Furthermore, in situ hybridization confirmed no detectable expression of DWT1 in the elongating internode (Fig. 5C), but high DWT1 expression in the panicle meristem including the primordia of primary and secondary branches, floral meristem, and leaf primordia surrounding these meristems (Fig. 5E–G). Consistent with qRT-PCR results, DWT1 transcripts were observed in the young embryo 10 days after fertilization (Fig. 5I), and in the endodermis and exodermis layers of the elongation zone in root tip (Fig. 5K). We could only observe the DWT1 protein in the young panicle but not in elongating internodes (Fig. 5M–R).
5、Un-elongated internodes in dwt1 have changed expression of genes involved in cell division and cell elongation
These results suggest that altered cytokinin signaling and reduced amount of active cytokinin may contribute to the reduced activity of cell division in dwt1.
6、DWT1 provides an activity required for GA promotion of cell elongation
Four genes encoding GA20-oxidases (OsGA20OX1, OsGA20OX2, OsGA20OX3, and OsGA20OX4), which are feedback inhibited by GA signaling, displayed increased expression in dwt1 (Fig. 7). Consistent with the reduced morphological response, the expression levels of OsGA20OX1, OsGA20OX2, OsGA20OX3, and OsGA20OX4 were less responsive to GA treatment in dwt1 un-elongated internodes than normal ones of the wild type (Fig. 8D), suggesting a defect in GA signaling in these internodes. SLENDER RICE1 (SLR1) is a nuclear-localized DELLA-domain protein that functions as a central suppressor of GA signaling in rice [33,34]. Compared with the wild type, slr1 mutants display a quick elongation of the basal internode at the seedling stage because of the constitutively activated GA response. To determine the genetic relationship between SLR1 and DWT1, we crossed dwt1 with slr1, and identified the double mutant by genotyping (see methods). The slr1 dwt1 double mutant showed a subset of twisted and shorter internodes similar to dwt1 plants (Fig. 8E, Fig. S8 C, F), while other internodes elongated as those of slr1 mutant, suggesting that the DWT1-dependent activity is required for the internode elongation in the absence of SLR1.
Shoot branching is one of the most important developmental processes that determine crop yields. While most wild plants have dominant main shoot and weaker branches, two extreme branching traits have been selected during the domestication of cereal crops. Some crops, such as maize and sorghum, exhibit enhanced apical dominance and suppression of branches compared to their highly branched ancestors. Suppression of branch development reduces the competition for resources and thus enhances the productivity of the main shoot. In contrast, other cultivated species, including rice, wheat and barley, have been selected for multiple tillers that develop from buds at the basal un-elongated nodes of the main shoot but bearing panicles that reach similar size as the main shoot. The intra-plant panicle uniformity is essential for the high yield in these species, but the underlying mechanism has remained elusive. Our study identified DWT1, a WOX member, as an essential genetic component specifying this trait in rice.
Labs working on this gene
1 State Key Laboratory of Hybrid Rice, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
2 Key Laboratory of Plant Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing, China
3 Graduate University of the Chinese Academy of Sciences, Beijing, China
4 Department of Plant Biology, Carnegie Institution for Science, Stanford, California, United States of America
1. Wenfei Wang;Gang Li;Jun Zhao;Huangwei Chu;Wenhui Lin;Dabing Zhang;Zhiyong Wang;Wanqi Liang
DWARF TILLER1, a WUSCHEL-Related Homeobox Transcription Factor, Is Required for Tiller Growth in Rice PLoS Genetics, 2014, 10(3): e1004154
Conserved hypothetical protein
NM_001050343.1 GI:115439056 GeneID:4326320
Oryza sativa Japonica Group Os01g0667400, complete gene.
Oryza sativa Japonica Group
ORGANISM Oryza sativa Japonica Group Eukaryota; Viridiplantae; Streptophyta; Embryophyta; Tracheophyta; Spermatophyta; Magnoliophyta; Liliopsida; Poales; Poaceae; BEP clade; Ehrhartoideae; Oryzeae; Oryza.
|Sequence Coding Region||
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<gbrowseImage2> name=NC_008394:29046116..29047653 source=RiceChromosome01 preset=GeneLocation </gbrowseImage2>
<aaseq>MSVTTAMDLLSPLAAACHQQMLYQGQPLESPPAPAPKVHGIVPH DEPVFLQWPQSPCLSAVDLGAAILGGQYMHLPVPAPQPPSSPGAAGMFWGLCNDVQAP NNTGHKSCAWSAGLGQHWCGSADQLGLGKSSAASIATVSRPEEAHDVDATKHGLLQYG FGITTPQVHVDVTSSAAGVLPPVPSSPSPPNAAVTVASVAATASLTDFAASAISAGAV ANNQFQGTLFVL</aaseq>