Wakana Tanaka,a,b Yoshihiro Ohmori,a,1 Tomokazu Ushijima,c Hiroaki Matsusaka,c Tomonao Matsushita,c Toshihiro Kumamaru,c Shigeyuki Kawano,b and Hiro-Yuki Hiranoa,2
Axillary shoot formation is a key determinant of plant architecture.
Formation of the axillary shoot is regulated by initiation of the
axillary meristem or outgrowth of the axillary bud. Here, we show that
rice (Oryza sativa) TILLERS ABSENT1 (TAB1; also known as Os WUS), an
ortholog of Arabidopsis thaliana WUS, is required to initiate axillary
meristem development. We found that formation of the axillary meristem
in rice proceeds via a transient state, which we term the premeristem,
characterized by the expression of OSH1, a marker of indeterminate cells
in the shoot apical meristem. In the tab1-1 (wus-1) mutant, however,
formation of the axillary meristem is arrested at various stages of the
premeristem zone, and OSH1 expression is highly reduced. TAB1/WUS is
expressed in the premeristem zone, where it shows a partially
overlapping pattern with OSH1. It is likely, therefore, that TAB1 plays
an important role in maintaining the premeristem zone and in promoting
the formation of the axillary meristem by promoting OSH1 expression.
Temporal expression patterns of WUSCHEL-RELATED HOMEOBOX4 (WOX4)
indicate that WOX4 is likely to regulate meristem maintenance instead of
TAB1 after establishment of the axillary meristem. Lastly, we show that
the prophyll, the first leaf in the secondary axis, is formed from the
premeristem zone and not from the axillary meristem.