Abstract: Rice tiller is a specialized grain-bearing branch originated from an axillary bud generated on the basal internode. Tiller number and tiller angle are two components of rice architecture and important agronomic traits, which are key determinants of plant density and panicle number, hence tightly associated with grain yield. It is an important topic to elucidate the underlying mechanism in regulation of tiller development. Some classical tiller-related genes, such as MONOCULM 1(MOC1), IDEAL PLANT ARCHITECTURE1 (IPA1), PROSTRATE GROWTH1 (PROG1), and LAZY1, were reported to regulate tiller number or tiller angle. In addition to the genetic basis (genes), some environmental factors, such as fertilizer and gravity, and some endogenous phytohormones, such as auxin and strigolactone, also affect tiller development. With the emergence and development of gene editing technology, as well as the utilization of GWAS and other new technologies, much progress has been gained recently including cloning of NITROGEN-MEDIATED TILLER GROWTH RESPONSE 5 (NGR5), TEOSINTE BRANCHED 1/CYCLOIDEA/PROLIFERATING CELL FACTOR 19 (OsTCP19), LAZY2 to LAZY6; the discovery of regulatory roles of strigolactones and root microbiota in tiller number, and so on. Especially, functional characterization of NGR5 and OsTCP19 revealed the mechanism of nitrogen in regulation of tiller number. These progress not only throws light on uncovering the mechanism to modulate tillering, but also provides gene resources for genetic improvement. In this review, we tried to summarize the mechanism and factors regulating tiller development in-depth, especially classical genes and great progress are highlighted, and meanwhile the challenges and opportunities are discussed. Overall, this review provides a comprehensive overview for the underlying mechanism of modulating tiller number and angle.

Key words: Rice, tiller number, tiller angle, nitrogen supply, MOC1, LAZY1, IPA1