SUMMARYEnolases are key glycolytic enzymes that are highly conserved in prokaryotic and eukaryotic organisms, and are among the most abundant cytosolic proteins. In this study we provide evidence that activity of the enolase ENO2 is essential for the growth and development of plants. We show that Arabidopsis plants with compromised ENO2 function, which were generated by mutating the LOS2/ENO2 locus, have severe cellular defects, including reduced cell size and defective cell differentiation with restricted lignification. At the tissue and organ level LOS2/ENO2-deficient plants are characterized by the reduced growth of shoots and roots, altered vascular development and defective secondary growth of stems, impaired floral organogenesis and defective male gametophyte function, resulting in embryo lethality as well as delayed senescence. These phenotypes correlate with reduced lignin and increased salicylic acid contents as well as altered fatty acid and soluble sugar composition. In addition to an enolase the LOS2/ENO2 locus encodes the transcription factor AtMBP-1, and here we reveal that this bifunctionality serves to maintain the homeostasis of ENO2 activity. In summary, we show that in plants enolase function is required for the formation of chorismate-dependent secondary metabolites, and that this activity is feedback-inhibited by AtMBP-1 to enable the normal development and reproductive success of plants.

Plants show an indeterminate mode of growth by the activity of organ forming stem cell niches in apically positioned meristems. The correct formation and activity of these meristems are a prerequisite for their adaptive development and also allow the maintenance of organogenesis under adverse circumstances such as wounding. Mutation of the putative Arabidopsis () Glu carboxypeptidase ALTERED MERISTEM PROGRAM1 (AMP1) results in Arabidopsis plants with enlarged shoot apical meristems, supernumerary stem cell pools, and higher leaf formation rate. AMP1 deficiency also causes exaggerated de novo formation of shoot meristems. The activity of AMP1 has been implicated in the control of microRNA (miRNA)-dependent translation; however, it is not known how this function contributes to the shoot meristem defects. Here, we show that the transcription factor RAP2.6L is upregulated in the Arabidopsis mutant. Overexpression of RAP2.6L in the wild type causes mutant-related phenotypic and molecular defects, including enhanced shoot regeneration in tissue culture. Conversely, inhibition of RAP2.6L in the mutant suppresses stem cell hypertrophy and the regenerative capacity. We further provide evidence that is under direct transcriptional control of miRNA-regulated class III homeodomain-Leu zipper (HD-ZIP III) proteins, key regulators of shoot meristem development, which overaccumulate in the mutant. Our results reveal a transcription factor module acting downstream of in the control of shoot stem cell niche patterning. By positioning the HD-ZIP III/RAP2.6L module downstream of AMP1 function, we provide a mechanistic link between the role of AMP1 in miRNA-mediated translational repression and shoot stem cell specification.

To select adequate wheat germplasms for genetic transformation, tissue culture efficiency of 21 different wheat lines (Einkorn, Emmer, Durum wheat, etc.) were compared, along with two different explants, namely, immature embryo and mature embryo. The results showed that the average differentiation rate and regeneration rate of immature embryo calli (46.5 and 20.82 %) were better than those for mature embryo calli (14.03 and 4.37 %). The best genotypes for immature embryo callus culture were 'Ningchun 16' and 'Ei 15', 'Xiaoyan 22', followed by 'Durum 332' and 'Tr 256'. The best genotypes for mature embryo callus culture were 'Ying 4286', 'Yunyin 01', and 'Xiaoyan 22'. To analyze how physiological and biochemical settings influence the totipotency of calli, different physiological and biochemical indices were analyzed. Differences between immature embryo callus and mature embryo callus were significant, as well as differences of most indices among different wheat types. The interaction effects between explant types and genotypes were also significant. Correlation analysis results showed that the total phenol and soluble sugar contents were significantly correlated with callus differentiation and regeneration rates.

) is a member of the M28 family of carboxypeptidases with a pivotal role in plant development and stress adaptation. Its most prominent mutant defect is a unique hypertrophic shoot phenotype combining a strongly increased organ formation rate with enhanced meristem size and the formation of ectopic meristem poles. However, so far the role of AMP1 in shoot development could not be assigned to a specific molecular pathway nor is its biochemical function resolved. In this work we evaluated the level of functional conservation between AMP1 and its human homolog HsGCPII, a tumor marker of medical interest. We show that HsGCPII cannot substitute AMP1 in planta and that an HsGCPII-specific inhibitor does not evoke amp1-specific phenotypes. We used a chemical genetic approach to identify the drug hyperphyllin (HP), which specifically mimics the shoot defects of amp1, including plastochron reduction and enlargement and multiplication of the shoot meristem. We assessed the structural requirements of HP activity and excluded that it is a cytokinin analog. HP-treated wild-type plants showed amp1-related tissue-specific changes of various marker genes and a significant transcriptomic overlap with the mutant. HP was ineffective in amp1 and elevated the protein levels of PHAVOLUTA, consistent with the postulated role of AMP1 in miRNA-controlled translation, further supporting an AMP1-related mode of action. Our work suggests that plant and animal members of the M28 family of proteases adopted unrelated functions. With HP we provide a tool to characterize the plant-specific functions of this important class of proteins.Arabidopsis ALTERED MERISTEM PROGRAM1 (AMP1, At3G54720, MEROPS ID: M28.007) belongs to the Zn 2+

Higher plants can continuously form new organs by the sustained activity of pluripotent stem cells. These stem cells are embedded in meristems, where they produce descendants, which undergo cell proliferation and differentiation programs in a spatiotemporally-controlled manner. Under certain conditions, pluripotency can be reestablished in descending cells and this reversion in cell fate appears to be actively suppressed by the existing stem cell pool. Mutation of the putative carboxypeptidase ALTERED MERISTEM PROGRAM1 (AMP1) in Arabidopsis causes defects in the suppression of pluripotency in cells normally programmed for differentiation, giving rise to unique hypertrophic phenotypes during embryogenesis as well as in the shoot apical meristem. A role of AMP1 in the miRNAdependent control of translation has recently been established, however, how this activity is connected to its developmental functions is not resolved. Here we identify members of the cytochrome P450 clade CYP78A to act in parallel with AMP1 to control cell fate in Arabidopsis. Mutation of CYP78A5 and its close homolog CYP78A7 in a cyp78a5,7 double mutant caused suspensor-to-embryo conversion and ectopic stem cell pool formation in the shoot meristem, phenotypes characteristic for amp1. The tissues affected in the mutants showed pronounced expression levels of AMP1 and CYP78A5 in wild type. A comparison of mutant transcriptomic responses revealed an intriguing degree of overlap and highlighted alterations in protein lipidation processes. Moreover, we also found elevated protein levels of selected miRNA targets in cyp78a5,7. Based on comprehensive genetic interaction studies we propose a model in which both enzyme classes act on a common downstream process to sustain cell fate decisions in the early embryo and the shoot apical meristem.