Os06g0665400

Function

The temporal and spatial control of meristem identity is a key element in plant development.Through certain research,we found out that the rice aberrant panicle organization 1 (apo1) mutants revealed that APO1 positively controls spikelet number by suppressing the precocious conversion of inflorescence meristems to spikelet meristems.Besides, the rice aberrant panicle organization 2 (apo2) mutant which exhibits small panicles reduces number of primary branches due to the precocious formation of spikelet meristems.

To better understand the molecular mechanisms that regulate inflorescence and flower architecture,To elucidate its molecular function, we isolated the APO1 and AP02 gene using a map-based strategy. And through analyses of phenotypes and gene expression,we revealed that phenotypic analyses of apo1 and floral homeotic double mutants demonstrate that APO1 positively regulates class-C floral homeotic genes, but not class-B genes. Molecular studies revealed that APO1 encodes an F-box protein, an ortholog of Arabidopsis UNUSUAL FLORAL ORGAN (UFO), which is a positive regulator of class-B genes. Over expression of APO1 caused an increase in inflorescence branches and spikelets. As the mutant inflorescences and flowers differed considerably between apo1 and ufo, the functions of APO1 and UFO appear to have diverged during evolution.

In addition,APO2 is identical to previously reported RFL gene, the rice ortholog of the Arabidopsis LEAFY(LFY) gene. Further analysis indicated that APO2/RFL and APO1, the rice ortholog of Arabidopsis UNUSUAL FLORAL ORGANS, act cooperatively to control inflorescence and flower development. The present study revealed functional differences between APO2/RFL and LFY. In particular, APO2/RFL and LFY act oppositely on inflorescence development. Therefore, the genetic mechanisms for controlling inflorescence architecture have evolutionarily diverged between rice (monocots) and Arabidopsis (eudicots). Figure 1.Phenotypes of apo1.(a) Panicle structure.(b)Top view of the wild-type inflorescence.(c) Side view of the apo1-2inflorescence.(d) Wild-type flower comprising two lodicules (arrowhead), six stamens and one pistil(e) apo1-2 flower comprising two lodicules (arrowheads), two lodiculestamen mosaic organs (arrows), three stamens and three pistils.(f) SEM image of apo1-1 flower.(g) In situ expression of DL gene in wild-type (left)and apo1-1(right) flowers.DL is expressed in normal and extopic carpel primordia (arrowheads).(h), (i) Schematic representation of wild-type (f) and apo1 (g) flowers. (j), (k)A model of floral organ identity in wild type (h) and apo1 (i). Abbreviations: ca,carpel; cg, mosaic organ between carpel and glume; le, lemma; lo, lodicule; pa,palea; st, stamen. Scale bars = 10 cm in (a), and 50 lm in (b) and (c).