SUMMARYMicroRNAs (miRNAs) have emerged as key regulators of gene expression at the post-transcriptional level in both plants and animals. However, the specific functions of MIRNAs (MIRs) and the mechanisms regulating their expression are not fully understood. Previous studies showed that miR160 negatively regulates three genes that encode AUXIN RESPONSE FACTORs (ARF10,. Here, we characterized floral organs in carpels (foc), an Arabidopsis mutant with a Ds transposon insertion in the 3¢ regulatory region of MIR160a. foc plants exhibit a variety of intriguing phenotypes, including serrated rosette leaves, irregular flowers, floral organs inside siliques, reduced fertility, aberrant seeds, and viviparous seedlings. Detailed phenotypic analysis showed that abnormal cell divisions in the basal embryo domain and suspensor led to diverse defects during embryogenesis in foc plants. Further analysis showed that the 3¢ region was required for the expression of MIR160a. The accumulation of mature miR160 was greatly reduced in foc inflorescences. In addition, the expression pattern of ARF16 and -17 was altered during embryo development in foc plants. foc plants were also deficient in auxin responses. Moreover, auxin was involved in regulating the expression of MIR160a through its 3¢ regulatory region. Our study not only provides insight into the molecular mechanism of embryo development via MIR160a-regulated ARFs, but also reveals the mechanism regulating MIR160a expression.

Potassium (K) influences the photosynthesis process in a number of ways; however, the mechanisms underlying the photosynthetic response to differences in K supply are not well understood. Concurrent measurements of gas exchange and chlorophyll fluorescence were made to investigate the effect of K nutrition on photosynthetic efficiency and mesophyll conductance (g(m)) in hickory seedlings (Carya cathayensis Sarg.) in a greenhouse. The results show that leaf K concentrations < 0.7-0.8% appeared to limit the leaf net CO2 assimilation rate (A), and that the relative limitation of photosynthesis due to g(m) and stomatal conductance (g(s)) decreased with increasing supplies of K. However, a sensitivity analysis indicated that A was most sensitive to the maximum carboxylation rate of Rubisco (V(c,max)) and the maximum rate of electron transport (J(max)). These results indicate that the photosynthetic rate is primarily limited by the biochemical processes of photosynthesis (V(c,max) and J(max)), rather than by g(m) and g(s) in K-deficient plants. Additionally, g(m) was closely correlated with g(s) and the leaf dry mass per unit area (M(A)) in hickory seedlings, which indicates that decreased g(m) and g(s) may be a consequence of leaf anatomical adaptation.

MicroRNAs (miRNAs) control gene expression as key negative regulators at the post-transcriptional level. MiR160 plays a pivotal role in Arabidopsis growth and development through repressing expression of its target AUXIN RESPONSE FACTOR (ARF) genes; however, the function of miR160 in monocots remains elusive. In this study, we found that the mature rice miR160 (OsmiR160) was mainly derived from OsMIR160a and OsMIR160b genes. Among four potential OsmiR160 target OsARF genes, the OsARF18 transcript was cleaved at the OsmiR160 target site. Rice transgenic plants (named mOsARF18) expressing an OsmiR160-resistant version of OsARF18 exhibited pleiotropic defects in growth and development, including dwarf stature, rolled leaves, and small seeds. mOsARF18 leaves were abnormal in bulliform cell differentiation and epidermal cell division. Starch accumulation in mOsARF18 seeds was also reduced. Moreover, auxin induced expression of OsMIR160a, OsMIR160b, and OsARF18, whereas expression of OsMIR160a and OsMIR160b as well as genes involved in auxin signaling was altered in mOsARF18 plants. Our results show that negative regulation of OsARF18 expression by OsmiR160 is critical for rice growth and development via affecting auxin signaling, which will advance future studies on the molecular mechanism by which miR160 fine-tunes auxin signaling in plants.

Gangliosides, sialic acid-bearing glycosphingolipids, are highly enriched in the vertebrate nervous system.

Cell signaling pathways mediated by leucine-rich repeat receptor-like kinases (LRR-RLKs) are essential for plant growth, development, and defense. The EMS1 (EXCESS MICROSPOROCYTES1) LRR-RLK and its small protein ligand TPD1 (TAPETUM DETERMINANT1) play a fundamental role in somatic and reproductive cell differentiation during early anther development in Arabidopsis (Arabidopsis thaliana). However, it is unclear whether other cell surface molecules serve as coregulators of EMS1. Here, we show that SERK1 (SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE1) and SERK2 LRR-RLKs act redundantly as coregulatory and physical partners of EMS1. The SERK1/2 genes function in the same genetic pathway as EMS1 in anther development. Bimolecular fluorescence complementation, Förster resonance energy transfer, and coimmunoprecipitation approaches revealed that SERK1 interacted biochemically with EMS1. Transphosphorylation of EMS1 by SERK1 enhances EMS1 kinase activity. Among 12 in vitro autophosphorylation and transphosphorylation sites identified by tandem mass spectrometry, seven of them were found to be critical for EMS1 autophosphorylation activity. Furthermore, complementation test results suggest that phosphorylation of EMS1 is required for its function in anther development. Collectively, these data provide genetic and biochemical evidence of the interaction and phosphorylation between SERK1/2 and EMS1 in anther development.