A rice tiller is a specialized grain-bearing branch that contributes greatly to grain yield. The MONOCULM 1 (MOC1) gene is the first identified key regulator controlling rice tiller number; however, the underlying mechanism remains to be elucidated. Here we report a novel rice gene, Tillering and Dwarf 1 (TAD1), which encodes a co-activator of the anaphase-promoting complex (APC/C), a multi-subunit E3 ligase. Although the elucidation of co-activators and individual subunits of plant APC/C involved in regulating plant development have emerged recently, the understanding of whether and how this large cell-cycle machinery controls plant development is still very limited. Our study demonstrates that TAD1 interacts with MOC1, forms a complex with OsAPC10 and functions as a co-activator of APC/C to target MOC1 for degradation in a cell-cycle-dependent manner. Our findings uncovered a new mechanism underlying shoot branching and shed light on the understanding of how the cell-cycle machinery regulates plant architecture.

Strigolactones (SLs), a group of terpenoid lactones derived from carotenoids, are plant hormones that control numerous aspects of plant development. Although the framework of SL signaling that the repressor DWARF 53 (D53) could be SL-dependently degraded via the SL receptor D14 and F-box protein D3 has been established, the downstream response genes to SLs remain to be elucidated. Here we show that the cytokinin (CK) content is dramatically increased in shoot bases of the rice SL signaling mutantd53. By examining transcript levels of all the CK metabolism-related genes after treatment with SL analog GR24, we identifiedCYTOKININ OXIDASE/DEHYDROGENASE 9(OsCKX9) as a primary response gene significantly up-regulated within 1 h of treatment in the wild type but not ind53. We also found that OsCKX9 functions as a cytosolic and nuclear dual-localized CK catabolic enzyme, and that the overexpression ofOsCKX9suppresses the browning ofd53calli. Both the CRISPR/Cas9-generatedOsCKX9mutants andOsCKX9-overexpressing transgenic plants showed significant increases in tiller number and decreases in plant height and panicle size, suggesting that the homeostasis ofOsCKX9plays a critical role in regulating rice shoot architecture. Moreover, we identified the CK-inducible rice type-A response regulatorOsRR5as the secondary SL-responsive gene, whose expression is significantly repressed after 4 h of GR24 treatment in the wild type but not inosckx9. These findings reveal a comprehensive plant hormone cross-talk in which SL can induce the expression ofOsCKX9to down-regulate CK content, which in turn triggers the response of downstream genes.

The breeding of cereals with altered gibberellin (GA) signaling propelled the ‘Green Revolution’ by generating semidwarf plants with increased tiller number. The mechanism by which GAs promote shoot height has been studied extensively, but it is not known what causes the inverse relationship between plant height and tiller number. Here we show that rice tiller number regulator MONOCULM 1 (MOC1) is protected from degradation by binding to the DELLA protein SLENDER RICE 1 (SLR1). GAs trigger the degradation of SLR1, leading to stem elongation and also to the degradation of MOC1, and hence a decrease in tiller number. This discovery provides a molecular explanation for the coordinated control of plant height and tiller number in rice by GAs, SLR1 and MOC1.

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Single nucleotide polymorphisms (SNPs) offer promise to forensic DNA analysts, but it remains uncertain whether a panel of individual identification SNPs can be as informative as the Combined DNA Index System short tandem repeats. Based on the highly accurate and publicly available HapMap SNP database (r21a) and a minor allele frequency cutoff of >or=0.45, we completed a genome-wide screen through 3,905,819 SNPs with internally modified computer programs and identified 1439 SNPs with high heterozygosity and low F(st) values among four populations (Utah Caucasian, Han Chinese, Tokyo Japanese, and Nigerian Yoruba). Using pyrosequencing technology, we studied six loci in a relatively large group of samples to determine whether these loci were as informative as the HapMap data suggest. These SNPs performed as expected in the Han Chinese in terms of heterozygosity and F(st). The 1439 identified SNPs should provide a comprehensive and reliable set of loci for identity and relationship testing.