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Floral organ development is fundamentally important to plant reproduction and seed quality, yet its underlying regulatory mechanisms are still largely unknown, especially in crop plants. In this study, we characterized rice null mutant
osarf19
, which was isolated from a T-DNA insertion pool. The mutant displayed three types of abnormal florets: an enlarged and degenerated palea, and an additional lemma. It also showed enlarged plant architecture, including elongated basal internodes and leaves. Cellular morphology and quantitative real-time PCR (qRT-PCR) analyses showed that cell elongation caused the enlarged organs. Transgenic RNA interference (RNAi) lines of
OsARF19
had similar phenotypes to the
osarf19
mutant, confirming the role of
OsARF19
in floral and vegetative organ development.
OsARF19
is expressed in various tissues, especially young panicles and basal internodes, which are elongated.
OsARF19
was induced by IAA (indole-3-acetic acid) treatment and functioned in the nucleus. By qRT-PCR analysis, we found that disruption of
OsARF19
increases expression levels of
OsYUCCA
and
OsPIN
family members, while reducing
OsGHs
transcription activity. The high auxin performance greatly upregulated two floral organ regulators,
OsMADS29
and
OsMADS22
, possibly responsible for palea abnormalities in
osarf19
. Our data provide new knowledge on the mechanisms of floral organ development, as well as possibilities in breeding for ideal plant architecture.