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Summary: Auxin regulates almost every aspect of plant growth and development and is perceived by the TIR1/AFB auxin co‐receptor proteins differentially acting in concert with specific Aux/IAA transcriptional repressors. Little is known about the diverse functions of TIR1/AFB family members in species other than Arabidopsis.We created targeted OsTIR1 and OsAFB2–5 mutations in rice using CRISPR/Cas9 genome editing, and functionally characterized the roles of these five members in plant growth and development and auxinic herbicide resistance.Our results demonstrated that functions of OsTIR1/AFB family members are partially redundant in grain yield, tillering, plant height, root system and germination. Ostir1, Osafb2 and Osafb4 mutants exhibited more severe phenotypes than Osafb3 and Osafb5. The Ostir1Osafb2 double mutant displays extremely severe defects in plant development. All five OsTIR1/AFB members interacted with OsIAA1 and OsIAA11 proteins in vivo. Root elongation assay showed that each Ostir1/afb2–5 mutant was resistant to 2,4‐dichlorophenoxyacetic acid (2,4‐D) treatment. Notably, only the Osafb4 mutants were strongly resistant to the herbicide picloram, suggesting that OsAFB4 is a unique auxin receptor in rice.Our findings demonstrate similarities and specificities of auxin receptor TIR1/AFB proteins in rice, and could offer the opportunity to modify effective herbicide‐resistant alleles in agronomically important crops. [ABSTRACT FROM AUTHOR]

The conserved miRNA393 family is thought to be involved in root elongation, leaf development and stress responses, but its role during seed germination and seedling establishment remains unclear. In this study, expression of the MIR393a/target module and its role in germinating rice ( Oryza sativa L.) seeds were investigated. β-Glucuronidase (GUS) analysis showed that MIR393a and OsTIR1 had spatial-temporal transcriptional activities in radicle roots, coleoptile tips and stomata cells, corresponding to a dynamic auxin response. miR393a promoted primary root elongation when rice seeds were germinated in air and inhibited coleoptile elongation and stomatal development when seeds were submerged. Under submergence, the expression of miR393a was inhibited, and then the auxin response was induced. In the process, OsTIR1 and OsAFB2, auxin receptor genes, were negatively regulated by miR393. We found that miR393a inhibited stomatal development and coleoptile elongation but promoted free indole acetic acid (IAA) accumulation in the rice coleoptile tips. In addition, exogenous abscisic acid (ABA) enhanced the expression of miR393 and inhibited coleoptile growth. Together, miR393a/target plays a role in coleoptile elongation and stomatal development via modulation of auxin signalling during seed germination and seedling establishment under submergence. This study provides new perspectives on the direct sowing of rice seeds in flooded paddy fields. [ABSTRACT FROM AUTHOR]

MicroRNA (miRNA)-mediated regulation of auxin signaling components plays a critical role in plant development. miRNA expression and functional diversity contribute to the complexity of regulatory networks of miRNA/target modules., This study functionally characterizes two members of the rice ( Oryza sativa) miR393 family and their target genes, OsTIR1 and OsAFB2 ( AUXIN SIGNALING F-BOX), the two closest homologs of Arabidopsis TRANSPORT INHIBITOR RESPONSE 1 ( TIR1)., We found that the miR393 family members possess distinctive expression patterns, with miR393a expressed mainly in the crown and lateral root primordia, as well as the coleoptile tip, and miR393b expressed in the shoot apical meristem. Transgenic plants overexpressing miR393a/b displayed a severe phenotype with hallmarks of altered auxin signaling, mainly including enlarged flag leaf inclination and altered primary and crown root growth. Furthermore, OsAFB2- and OsTIR1-suppressed lines exhibited increased inclination of flag leaves at the booting stage, resembling miR393-overexpressing plants. Moreover, yeast two-hybrid and bimolecular fluorescence complementation assays showed that OsTIR1 and OsAFB2 interact with OsIAA1., Expression diversification of miRNA393 implies the potential role of miRNA regulation during species evolution. The conserved mechanisms of the miR393/target module indicate the fundamental importance of the miR393-mediated regulation of auxin signal transduction in rice. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide (H2O2) is known to be a key player in apoptosis in animals. The components and pathways regulating H2O2-induced programmed cell death in plants, however, remain largely unknown. In the present study, rice transgenic lines overexpressing Bcl-2, a human apoptotic suppressor, were obtained. These transgenic lines showed increased tolerance to high levels of H2O2, resulting in increased seed germination rates, root elongation, root tip cell viability and chlorophyll retention compared to control lines. In the control lines, treatment with H2O2 resulted in DNA laddering and a clear terminal transferase dUTP nick end labeling signal, which are the hallmarks of programmed cell death. However, this effect was not detected in the Bcl-2-overexpressing transgenic lines. Further investigations indicated that Bcl-2 suppressed H2O2-induced programmed cell death but did not inhibit stress-elicited reactive oxygen species production in rice. RT-PCR revealed that the expression of the two vacuolar processing enzyme genes (i.e. OsVPE2 and OsVPE3) was dramatically induced by H2O2 in the wild-type line but not in the Bcl-2-overexpressing line. Moreover, treatment with H2O2 resulted in the disruption of the vacuolar membrane in the wild-type line. The expression levels of OsVPE1 and OsVPE4 did not significantly differ between the wild-type line and the transgenic line that was treated or untreated with H2O2. The similar roles of Bcl-2 and OsVPEs during endogenous reactive oxygen species-triggered programmed cell death were also confirmed by NaCl stress in rice. To our knowledge, the present study is the first to demonsatrate that Bcl-2 overexpression inhibits H2O2-induced programmed cell death and enhances H2O2 tolerance. We propose that Bcl-2 overexpression in rice suppresses the transcriptional activation of OsVPE2 and OsVPE3, but not of OsVPE1 or OsVPE4. [ABSTRACT FROM AUTHOR]