Elucidating the regulatory mechanisms of plant organ formation is an important component of plant developmental biology and will be useful for crop improvement applications. Plant organ formation, or organogenesis, occurs when a group of primordial cells differentiates into an organ, through a well-orchestrated series of events, with a given shape, structure and function. Research over the past two decades has elucidated the molecular mechanisms of organ identity and dorsalventral axis determinations. However, little is known about the molecular mechanisms underlying the successive processes. To develop an effective approach for studying organ formation at the molecular level, we generated organ-specific gene expression profiles (GEPs) reflecting early development in rice stamen. In this study, we demonstrated that the GEPs are highly correlated with early stamen development, suggesting that this analysis is useful for dissecting stamen development regulation. Based on the molecular and morphological correlation, we found that over 26 genes, that were preferentially up-regulated during early stamen development, may participate in stamen development regulation. In addition, we found that differentially expressed genes during early stamen development are clustered into two clades, suggesting that stamen development may comprise of two distinct phases of pattern formation and cellular differentiation. Moreover, the organ-specific quantitative changes in gene expression levels may play a critical role for regulating plant organ formation.
Summary• Abscisic acid (ABA) is known to function in plant stress responses and seed dormancy, and much is known about its detailed mechanisms of signal transduction. Recent studies suggest that this hormone may also play important roles in sugar signaling and assimilate distribution during fruit development. However, little is known about the role of ABA in actively growing or differentiating fruits and other plant organs or tissues.• To explore whether ABA functions during the early development of reproductive organs, we carried out ABA immunolocalization using monoclonal antibodies. The specific ABA accumulation pattern was verified by gas chromatography-mass spectrometry (GC-MS).• ABA was not only detected in primordial cells of flower organs, but was also detected in nursing cells (e.g. tapetum and integuments), which function in supplying nutrition for germ cell development.• These findings suggest that, in addition to its well-known function as a 'negative hormone', ABA may play some 'positive' roles during plant development, including possible involvement in the regulation of assimilate distribution.
Early embryogenesis is the most fundamental developmental process in biology. Screening of ethyl methanesulfonate (EMS)-mutagenized populations of Arabidopsis thaliana led to the identification of a zygote-lethal mutant embryonic factor 19 (fac19) in which embryo development was arrested at the elongated zygote to octant stage. The number of endosperm nuclei decreased significantly in fac19 embryos. Genetic analysis showed fac19 was caused by a single recessive mutation with typical mendelian segregation, suggesting equal maternal and paternal contributions of FAC19 towards zygotic embryogenesis. Positional cloning showed that FAC19 encodes a putative mitochondrial protein with 16 conserved pentatricopeptide repeat (PPR) motifs. The fac19 mutation caused a conversion from hydrophilic serine located in a previously unknown domain to hydrophobic leucine. Crosses between FAC19/fac19 and the T-DNA insertion mutants in the same gene failed to complement the fac19 defects, confirming the identity of the gene. This study revealed the critical importance of a PPR protein-mediated mitochondrial function in early embryogenesis.
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