Receptor-like kinase OsCR4 controls leaf morphogenesis and embryogenesis by fixing the distribution of auxin in rice

Cell differentiation is a key event in organ development;it involves auxin gradient formation, cell signaling, and transcriptional regulation. Yet, how these processes are orchestrated during leaf morphogenesis is poorly understood. Here, we demonstrate an essential role for the receptor-like kinase Os CR4 in leaf development. oscr4 loss-of-function mutants displayed short shoots and roots, with tiny,crinkly, or even dead leaves. The delayed outgrowth of the first three leaves and seminal root in oscr4 was due to defects in plumule and radicle formation during embryogenesis. The deformed epidermal,mesophyll, and vascular tissues observed in oscr4 leaves arose at the postembryo stage;the corresponding expression pattern of pro Os CR4:GUS in embryos and young leaves suggests that Os CR4 functions in these tissues. Signals from the auxin reporter DR5 rev:VENUS were found to be altered in oscr4 embryos and disorganized in oscr4 leaves, in which indole-3-acetic acid accumulation was further revealed by immunofluorescence. Os WOX3 A, which is auxin responsive and related to leaf development,was activated extensively and ectopically in oscr4 leaves, partially accounting for the observed lack of cell differentiation. Our data suggest that Os CR4 plays a fundamental role in leaf morphogenesis and embryogenesis by fixing the distribution of auxin.

Induction of Somatic Embryos in Arabidopsis Requires Local YUCCA Expression Mediated by the Down-Regulation of Ethylene Biosynthesis

Somatic embryogenesis is an important experimental model for studying cellular and molecular mechanisms of early embryo development. Although it has long been known that removal of exogenous auxin from medium results in somatic embryogenesis, the mechanisms underlying the initiation of somatic embryos （SEs） are poorly understood. In this study, we showed that YUCCAs （YUCs） encoding key enzymes in auxin biosynthesis are required for SE induction in Arabidopsis. To identify other factors mediating SE initiation, we performed transcriptional profiling and gene expres- sion analysis. The results showed that genes involved in ethylene biosynthesis and its responses were down-regulated during SE initiation. Ethylene level decreased progressively during SE initiation, whereas treatment with the metabolic precursor of ethylene, 1-aminocyclopropane-l-carboxylic acid （ACC）, or mutation of ETHYLENE-OVERPRODUCTION1 （ET01） disrupted SE induction, suggesting that ethylene plays a role in this process. Suppression of SE induction was also observed in the constitutive triple response 1 （ctrl） mutant, in which ethylene signaling was enhanced. These results indicate that down-regulation of not only ethylene biosynthesis, but also ethylene response is critical for SE induction. We further showed that ethylene disturbed SE initiation through inhibiting YUC expression that might be involved in local auxin biosynthesis and subsequent auxin distribution. Our results provide new information on the mechanisms of hormone-regulated SE initiation.