Search

In many plant species, petal abscission can be considered the final step of petal senescence. Cytokinins (CKs) are powerful suppressors of petal senescence; however, their role in petal abscission is ambiguous. Here, we observed that, in rose (Rosa hybrida), biologically active CK is accumulated during petal abscission and acts as an accelerator of the abscission process. Using a combination of reverse genetics, and molecular and biochemical techniques, we explored the roles of a LESION SIMULATING DISEASE1 (LSD1) family member RhLOL1 interacting with a bHLH transcription factor RhILR3 in CK-induced petal abscission. Silencing RhLOL1 delays rose petal abscission, while the overexpression of its ortholog SlLOL1 in tomato (Solanum lycopersicum) promotes pedicel abscission, indicating the conserved function of LOL1 in activating plant floral organ abscission. In addition, we identify a bHLH transcription factor, RhILR3, that interacts with RhLOL1. We show that RhILR3 binds to the promoters of the auxin signaling repressor auxin/indole-3-acetic acid (Aux/IAA) genes to inhibit their expression; however, the interaction of RhLOL1 with RhILR3 activates the expression of the Aux/IAA genes including RhIAA4-1. Silencing RhIAA4-1 delays rose petal abscission. Our results thus reveal a RhLOL1-RhILR3 regulatory module involved in CK-induced petal abscission via the regulation of the expression of the Aux/IAA genes.

High temperature during grain filling considerably reduces yield and quality in rice, but its molecular mechanisms are not fully understood. We investigated the functions of a seed preferentially expressed Aux/IAA gene, OsIAA29, under high temperature-stress in grain filling using CRISPR/Cas9, RNAi, and overexpression. We observed that the osiaa29 had a higher percentage of shrunken and chalkiness seed, as well as lower 1000-grain weight than ZH11 under high temperature. Meanwhile, the expression of OsIAA29 was induced and the IAA content was remarkably reduced in the ZH11 seeds under high temperature. In addition, OsIAA29 may enhance the transcriptional activation activity of OsARF17 through competition with OsIAA21 binding to OsARF17. Finally, chromatin immunoprecipitation quantitative real-time PCR (ChIP-qPCR) results proved that OsARF17 regulated expression of several starch and protein synthesis related genes (like OsPDIL1-1, OsSS1, OsNAC20, OsSBE1, and OsC2H2). Therefore, OsIAA29 regulates seed development in high temperature through competition with OsIAA21 in the binding to OsARF17, mediating auxin signaling pathway in rice. This study provides a theoretical basis and gene resources for auxin signaling and effective molecular design breeding. [ABSTRACT FROM AUTHOR]

We aimed to investigate abiotic stress (WAK, HvPIP1.1, HvPIP1.2, HvPIP1.3, HvPIP1.5, CYCD3, DREB2) and brassinosteroid-related gene (DWARF4) expressions in barley (Hordeum vulgare L. cv. “Hilal”) roots grown under different salt (150 and 250 mM), HBR (0.5 and 1 μM), and salt + HBR applications during 48 and 72 h at dark with their controls. Phylogenetic trees were also constructed to observe relationships among genes found in other plants. The expression of HvPIP1.2 and WAK reduced after salt treatment while HvPIP1.3, DREB2 and DWARF4 expressions increased. HvPIP1.1, HvPIP1.2, HvPIP1.3, HvPIP1.5 and DWARF4 expressions were upregulated under only HBR applications. Salt + HBR treatments increased HvPIP1.1, DREB2 and DWARF4 but decreased HvPIP1.2. Phylogenetic analyses indicated that Oryza sativa L. shared similar sequences with HvPIP1.5. CYCD3 could diverge relatively earlier from cyclin genes during evolution as it segregates in a distinct clade. Sorghum bicolor showed sequence homology with DREB2. Oryza australiensis L. and DWARF4 were found in the same clade. To our knowledge, this is the first detailed report related to salt stress and HBR applications in terms of the expression of different genes in barley, providing a valuable information for molecular breeding improvement of stress-related traits. [ABSTRACT FROM AUTHOR]

Summary Indole acetic acid (IAA/auxin) profoundly affects wood formation but the molecular mechanism of auxin action in this process remains poorly understood. We have cloned cDNAs for eight members of the Aux/IAA gene family from hybrid aspen (Populus tremula L. × Populus tremuloides Michx.) that encode potential mediators of the auxin signal transduction pathway. These genes designated as PttIAA1-PttIAA8 are auxin inducible but differ in their requirement of de novo protein synthesis for auxin induction. The auxin induction of the PttIAA genes is also developmentally controlled as evidenced by the loss of their auxin inducibility during leaf maturation. The PttIAA genes are differentially expressed in the cell types of a developmental gradient comprising the wood-forming tissues. Interestingly, the expression of the PttIAA genes is downregulated during transition of the active cambium into dormancy, a process in which meristematic cells of the cambium lose their sensitivity to auxin. Auxin-regulated developmental reprogramming of wood formation during the induction of tension wood is accompanied by changes in the expression of PttIAA genes. The distinct tissue-specific expression patterns of the auxin inducible PttIAA genes in the cambial region together with the change in expression during dormancy transition and tension wood formation suggest a role for these genes in mediating cambial responses to auxin and xylem development. [ABSTRACT FROM AUTHOR]

SummaryLateral root development is a post-embryonic organogenesis event that gives rise to most of the underground parts of higher plants. Auxin promotes lateral root formation, but the molecular mechanisms involved are still unknown. We have isolated a novel Arabidopsis mutant, solitary-root (slr ), which has reduced sensitivity to auxin. This dominant slr-1 mutant completely lacks lateral roots, and this phenotype cannot be rescued by the application of exogenous auxin. Analysis with cell-cycle and cell-differentiation markers revealed that the slr-1 mutation blocks cell divisions of pericycle cells in lateral root initiation. The slr-1 mutant is also defective in root hair formation and in the gravitropic responses of its roots and hypocotyls. Map-based positional cloning and isolation of an intragenic suppressor mutant revealed that SLR encodes IAA14, a member of the Aux/IAA protein family. Green fluorescent protein-tagged mutant IAA14 protein was localized in the nucleus, and the gain-of-function slr-1/iaa14 mutation decreased auxin-inducible BA -GUS gene expression in the root, suggesting that SLR/IAA14 acts as a transcriptional repressor. These observations indicate that SLR/IAA14 is a key regulator in auxin-regulated growth and development, particularly in lateral root formation. [ABSTRACT FROM AUTHOR]

Summary Aux/IAA proteins are short-lived transcriptional regulators involved in auxin signaling. Using Aux/IAA luciferase (LUC) fusion proteins expressed in Arabidopsis thaliana , we previously showed that rapid degradation of these proteins requires conserved Aux/IAA domain II and that exogenous auxin accelerates their degradation. To further examine auxin-mediated increases in proteolysis, the degradation of two other LUC fusion proteins, a non-cleavable ubiquitin LUC fusion (UB1–72::LUC) and SAUR15::LUC was determined in vivo in seedlings. Their half-lives were 20 ± 4 and 104 ± 10 min, respectively. SAUR15::LUC half-life was not affected by pre-incubation with 2,4-D. Auxin did not have an equivalent effect on UB(1–72)::LUC steady-state levels as compared to PsIAA6:LUC. LUC fused to an Aux/IAA domain II degraded more rapidly following auxin application, demonstrating that this region is sufficient for auxin-mediated acceleration of proteolysis. Hormonal cross-talk at the level of Aux/IAA proteolysis was examined. 1-aminocyclopropane-1-carboxylic acid (ACC), benzyladenine (BA), abscisic acid (ABA), and brassinolide (BL) did not affect the degradation rate of IAA1::LUC, and gibberellic acid (GA3 ) and salicylic acid (SA) did not specifically affect the steady-state levels of Aux/IAA::LUC proteins. An Aux/IAA::LUC transgene was crossed into the auxin resistant-1 (axr1–12 ) background. In axr1–12 , the half-life of PsIAA6(1–73)::LUC increased 4.5-fold, but proteolysis still accelerated in response to exogenous auxin. These data suggest that auxin is the only phytohormone that accelerates Aux/IAA proteolysis, and that this acceleration is specific for Aux/IAA proteins. In addition, AXR1 plays an important role in rapid basal proteolysis of Aux/IAA proteins, but is not required for auxin-mediated acceleration of their degradation. [ABSTRACT FROM AUTHOR]