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Lateral branching is an important determinant of shoot architec-ture and crop yield.The plant hormone strigolactone (SL) inhibits lateral bud outgrowth in various plant species.Deficiencies in SL biosynthesis and signal transduction result in excessive outgrowth of lateral buds (Stirnberg et al.,2002;Sorefan et al.,2003).Physiolog-ical and genetic analyses of the max/rms/d mutants have revealed that SL is derived from carotenoids (Beveridge,2006;Ongaro and Leyser,2008),which are a class of isoprenoid pigments synthesized in all photosynthetic organisms (Walter and Strack,2011).Carot-enoid biosynthesis occurs in plastids and begins with the condensa-tion of geranylgeranyl pyrophosphate to phytoene by phytoene synthase (Moise et al.,2014).Phytoene is then converted into all-trans-lycopene after desaturation by phytoene desaturase(PDS) and zeta-carotene desaturase (ZDS) and isomerization by carotenoid isomerase (CRTISO) and 15-cis-ζ-carotene isomerase(Z-ISO) (Fig.S1) (Park et al.,2002;Booker et al.,2004;Breitenbach and Sandmann,2005;Li et al.,2007).Z-lSO is a key enzyme located in chloroplast membranes,where it independently catalyzes isomer-ization from 9159'-tri-cis-ζ-carotene to 9,9'-di-cis-ζ-carotene;how-ever,its function can also be partially compensated by light (Beltrán et al.,2015).Although SLs are synthesized from carotenoids,it re-mains unclear whether carotenoid deficiency can lead to increased shoot branching phenotypes through its effects on SL biosynthesis.rnFrom the M2 generation of the gamma ray-irradiated japonica cultivar Chunjiang 06,we identified a rice mutant exhibiting mild dwarfism and moderately increased tiller number (Figs.1A and S2).We termed this mutant moderately increased tiller 1 (mit1).At the peak of the tillering and heading stages,mit1 plant height was reduced to about 80％ of that of wild type (VVT),and the tiller number was increased to twofold that of WT plants (Figs.1A-1C,S2B,S2E,S2F).Anatomical observation revealed that both the mit1 mutant and WT plants produced only one tiller bud per leaf axil (Fig.S2C).How-ever,tiller bud growth was faster in the mit1 mutant than in WT plants(Fig.S2C and S2D).Kinetic analysis showed that the VVT plant reached its maximum tillering capacity at six weeks after transplant-ing;this period was extended by one week in the mit1 mutant(Fig.S2F).Thus,the increased tiller number was caused by acceler-ated tiller bud outgrowth and sustained tillering capacity among early developed tillers.