Cyclin D1 and p22ack1 play opposite roles in plant growth and development

The genetic basis of traits associated with the evolution of serpentine endemism in monkeyflowers

The floras on chemically and physically challenging soils, such as gypsum, shale, and serpentine, are characterized by narrowly endemic species. The evolution of edaphic endemics may be facilitated or constrained by genetic correlations among traits contributing to adaptation and reproductive isolation across soil boundaries. The yellow monkeyflowers in the Mimulus guttatus species complex are an ideal system in which to examine these evolutionary patterns. To determine the genetic basis of adaptive and prezygotic isolating traits, we performed genetic mapping experiments with F2 hybrids derived from a cross between a serpentine endemic, M. nudatus, and its close relative M. guttatus. Few large effect and many small effect QTL contribute to interspecific divergence in life history, floral, and leaf traits, and a history of directional selection contributed to trait divergence. Loci contributing to adaptive traits and prezygotic reproductive isolation overlap, and their allelic effects are largely in the direction of species divergence. These loci contain promising candidate genes regulating flowering time and plant organ size. Together, our results suggest that genetic correlations among traits can facilitate the evolution of adaptation and speciation and may be a common feature of the genetic architecture of divergence between edaphic endemics and their widespread relatives.

Overexpression of Physcomitrium patens cell cycle regulators leads to larger gametophytes

Regulation of cell division is crucial for the development of multicellular organisms, and in plants, this is in part regulated by the D-type cyclins (CYCD) and cyclin-dependent kinase A (CDKA) complex. Cell division regulation in Physcomitrium differs from other plants, by having cell division checks at both the G1 to S and G2 to M transition, controlled by the CYCD1/CDKA2 and CYCD2/CDKA1 complexes, respectively. This led us to hypothesize that upregulation of cell division could be archived in Bryophytes, without the devastating phenotypes observed in Arabidopsis. Overexpressing lines of PpCYCD1, PpCYCD2, PpCDKA1, or PpCDKA2 under Ubiquitin promotor control provided transcriptomic and phenotypical data that confirmed their involvement in the G1 to S or G2 to M transition control. Interestingly, combinatorial overexpression of all four genes produced plants with dominant PpCDKA2 and PpCYCD1 phenotypes and led to plants with twice as large gametophores. No detrimental phenotypes were observed in this line and two of the major carbon sinks in plants, the cell wall and starch, were unaffected by the increased growth rate. These results show that the cell cycle characteristics of P. patens can be manipulated by the ectopic expression of cell cycle regulators.

Transcriptome sequencing analysis of maize embryonic callus during early redifferentiation

BACKGROUND

Maize is one of the primary crops of genetic manipulation, which provides an excellent means of promoting stress resistance and increasing yield. However, the differences in induction and regeneration capacity of embryonic callus (EC) among various genotypes result in genotypic dependence in genetic transformation.

RESULTS

In this study, embryonic calli of two maize inbred lines with strong redifferentiation capacity and two lines with weak redifferentiation capability were separately subjected to transcriptome sequencing analysis during the early redifferentiation stages (stage I, 1-3 d; stage II, 4-6 d; stage III, 7-9 d) along with their corresponding controls. A total of ~ 654.72 million cDNA clean reads were yielded, and 62.64%~ 69.21% clean reads were mapped to the reference genome for each library. In comparison with the control, the numbers of differentially expressed genes (DEGs) for the four inbred lines identified in the three stages ranged from 1694 to 7193. By analyzing the common and specific DEGs of the four materials, we found that there were 321 upregulated genes and 386 downregulated genes identified in the high-regeneration lines (141 and DH40), whereas 611 upregulated genes and 500 downregulated genes were specifically expressed in the low-regeneration lines (ZYDH381-1 and DH3732). Analysis of the DEG expression patterns indicated a sharp change at stage I in both the high- and low-regeneration lines, which suggested that stage I constitutes a crucial period for EC regeneration. Notably, the specific common DEGs of 141 and DH40 were mainly associated with photosynthesis, porphyrin and chlorophyll metabolism, ribosomes, and plant hormone signal transduction. In contrast, the DEGs in ZYDH381-1 and DH3732 were mainly related to taurine and hypotaurine metabolism, nitrogen metabolism, fatty acid elongation, starch and sucrose metabolism, phenylpropanoid biosynthesis, and plant circadian rhythm. More importantly, WOX genes, which have an ancestral role in embryo development in seed plants and promote the regeneration of transformed calli, were specifically upregulated in the two high-regeneration lines.

CONCLUSIONS

Our research contributes to the elucidation of molecular regulation during early redifferentiation in the maize embryonic callus.

The D-type cyclin gene (Nicta;CycD3;4) controls cell cycle progression in response to sugar availability in tobacco

D-type cyclins play key roles in the G1-to-S phase transition that occurs in response to nutrient and hormonal signals. In higher plants, sucrose is the major transported carbon source, and is likely to be a major determinant of cell division. To elucidate how sugar affects on the regulation of cell cycle machinery and plant development, we examined the role of carbon sources on the expression of cell-cycle-related genes in transgenic tobacco plants overexpressing Nicta;CycD3;4. The Nicta;CycD3;4 overexpressed transgenic plants showed accelerated growth and remarkable increase in the number of cells in the S and G2 phases in response to sucrose concentrations. Increased expressions level of Nicta;CycD3;4 gene was observed in transgenic tobacco plants grown on 1/2 strength MS medium supplemented with a high concentration of sugar. Moreover, the expression of sugar-sensing-related gene, invertase, was also maintained at a high level in transgenic tobacco plants with elevated sugar availability. These findings indicate that sugar availability plays a role during the G1 phase and the transition of the G1-to-S phase of cell cycle by controlling the expression of Nicta;CycD3;4.

Transgenic tobacco plants overexpressing the Nicta; CycD3; 4 gene demonstrate accelerated growth rates

D-type cyclins control the onset of cell division and the response to extracellular signals during the G1 phase. In this study, we transformed a D-type cyclin gene, Nicta;CycD3;4, from Nicotiana tabacum using an Agrobacterium-mediated method. A predicted 1.1 kb cyclin gene was present in all of the transgenic plants, but not in wild-type. Northern analyses showed that the expression level of the Nicta;CycD3;4 gene in all of the transgenic plants was strong when compared to the wild-type plants, suggesting that Nicta;CycD3;4 gene driven by the CaMV 35S promoter was being overexpressed. Our results revealed that transgenic plants overexpressing Nicta;CycD3;4 had an accelerated growth rate when compared to wild-type plants, and that the transgenic plants exhibited a smaller cell size and a decreased cell population in young leaves when compared to wild-type plants.

Mechanism of leaf-shape determination

Biodiversity of plant shape is mainly attributable to biodiversity of leaf shape and the shape of floral organs, the modified leaves. However, the exact mechanisms of leaf-shape determination remain unclear due to the complexity of flat-structure organogenesis that includes the simultaneous cell cycling and cell enlargement in primordia. Recent studies in developmental and molecular genetics have revealed several important aspects of leaf-shape control mechanisms. For example, understanding of polar control in leaf-blade expansion has advanced greatly. A curious phenomenon called "compensated cell enlargement" found in leaf organogenesis studies should also provide interesting clues regarding the mechanisms of multicellular organ development. This paper reviews recent research findings with a focus on leaf development in Arabidopsis thaliana.

Secretome analysis reveals an Arabidopsis lipase involved in defense against Alternaria brassicicola

The Arabidopsis thaliana secretome was analyzed by the proteomic approach, which led to the identification of secreted proteins implicated in many aspects of cell biology. We then investigated the change in the Arabidopsis secretome in response to salicylic acid and identified several proteins involved in pathogen response. One of these, a secreted lipase with a GDSL-like motif designated GDSL LIPASE1 (GLIP1), was further characterized for its function in disease resistance. glip1 plants were markedly more susceptible to infection by the necrotrophic fungus Alternaria brassicicola compared with the parental wild-type plants. The recombinant GLIP1 protein possessed lipase and antimicrobial activities that directly disrupt fungal spore integrity. Furthermore, GLIP1 appeared to trigger systemic resistance signaling in plants when challenged with A. brassicicola, because pretreatment of the glip1 mutant with recombinant GLIP1 protein inhibited A. brassicicola-induced cell death in both peripheral and distal leaves. Moreover, glip1 showed altered expression of defense- and ethylene-related genes. GLIP1 transcription was increased by ethephon, the ethylene releaser, but not by salicylic acid or jasmonic acid. These results suggest that GLIP1, in association with ethylene signaling, may be a critical component in plant resistance to A. brassicicola.

Overexpression of Arabidopsis ACK1 alters leaf morphology and retards growth and development

Cyclin dependent kinases (CDKs) play important roles in the plant cell cycle, a highly coordinated process in plant growth and development. To understand the regulatory network involving the CDKs, we have examined the role of ACK1, a gene that has significant homology to known ICKs (inhibitors of CDKs), but occupies a distinct branch of the ICK phylogenetic tree. Overexpression of ACK1 in transgenic Arabidopsis significantly inhibited growth, leading to effects such as serration of leaves, as a result of strong inhibition of cell division in the leaf meristem. ACK1 transgenic plants also differed morphologically from control Arabidopsis plants, and the cells of ACK1 transgenics were more irregular than the corresponding cells of control plants. These results suggest that ACK1 acts as a CDK inhibitor in Arabidopsis, and that the alterations in leaf shape may be the result of restricted cell division.