Fertilisation and cell cycle in angiosperms

Fertilisation is the result of successful fusion of female and male gametes, forming a zygote that develops into the embryo. From the perspective of cell cycle control, fertilisation is a hat‐trick. Firstly, the generation of gametes depends on the generation of haploid spores by meiosis and a sequence of mitotic divisions. Mitosis is required to produce the cells of the gametophyte, closely associated with differential fate acquisition. Secondly, cell cycle progression in both male and female gametes has to be synchronised in order to avoid chromosomal imbalance at karyogamy, and last but not least, the cell cycle should only be relaunched after a successful fusion. Here, we seek to survey our current knowledge of these processes from a cell cycle perspective and explore possible mechanisms involved in cell cycle control and coordination

Effect of adjuvants on the efficiency of benthiavalicarb plus mancozeb (Valbon 1.6 kg/ha) on the control of late blight in potato

Industrial adjuvants were tested in combination with benthiavalicarb plus mancozeb (Valbon 1.6 kg/ha) in the field to investigate their efficacy on foliar late blight caused by Phytophthora infestans. The tested adjuvant-fungicide treatments for late blight control were applied 6 times at 7-day intervals. The effect of the adjuvant-fungicide treatments on epidemic development, tuber blight and tuber yields were determined. Because of the favourable weather conditions a high disease pressure could be observed. The incidence of foliage blight was scored and at the end of the growing season the disease level was lower in plots sprayed with the Valbon-adjuvant combinations than in plots treated with only Valbon. The addition of an adjuvant had a clearly positive effect on the tuber yield although the differences were not significant. In the plots treated with Valbon 6.9 % infected tubers were observed. The mean tuber infection of plots sprayed with the Valbon-adjuvant combinations fluctuated between 2.3 and 15.6 %

D-type cyclins control cell division and developmental rate during Arabidopsis seed development

Seed development in Arabidopsis is characterized by stereotypical division patterns, suggesting that coordinated control of cell cycle may be required for correct patterning and growth of the embryo and endosperm. D-type cyclins (CYCD) are key cell cycle regulators with roles in developmental processes, but knowledge regarding their involvement in seed development remains limited. Here, a family-wide gene expression, and loss- and gain-of-function approach was adopted to reveal additional functions for CYCDs in the development of seed tissues. CYCD genes have both discrete and overlapping tissue-specific expression patterns in the seed as revealed by GUS reporter gene expression. Analysis of different mutant combinations revealed that correct CYCD levels are required in seed development. The CYCD3 subgroup is specifically required as its loss caused delayed development, whereas overexpression in the embryo and endosperm of CYCD3;1 or a previously uncharacterized gene, CYCD7;1, variously leads to induced proliferation, abnormal phenotypes, and elevated seed abortion. CYCD3;1 overexpression provoked a delay in embryonic developmental progression and abnormalities including additional divisions of the hypophysis and suspensor, regions where CYCD3 genes are normally expressed, but did not affect endosperm development. Overexpression of CYCD7;1, not normally expressed in seed development, promoted overgrowth of both embryo and endosperm through increased division and cell enlargement. In contrast to post-germination growth, where pattern and organ size is not generally related to division, results suggest that a close control of cell division through regulation of CYCD activity is important during seed development in conferring both developmental rate and correct patterning

Cell size and cell cycle progression: the cyclin-dependent kinase link in green algae

The coordination of cell growth and cell division is a fundamental problem in biology. The experiments with unicellular algae of Zachleder et al. (2019) show that up-regulation of cyclin-dependent kinase (CDK) activity can drive cell progression even when biosynthesis is reduced, indicating that the main link between cell growth and cell division is CDK activity rather than overall biosynthesis. Understanding this coupling between cellular growth and CDK activity will be important not just in these algae, but also in higher plants

Commercial processing of Oriental lilies affects bud opening and metabolic dynamics

Lilies are a high value cut flower typically producing 4–5 flowers per stem, but the opening of young buds of Oriental hybrid lilies is often affected in cut flowers. Commercial treatment includes harvesting of the stem when the oldest bud is closed and at turning colour, approximately 2 ds before it would open on the plant. Stems are then rehydrated, stored chilled for up to 72 h and transported dry. To understand the effect of commercial treatment on the nutrient status metabolomes were compared throughout bud opening from different positions on the stem. At each developmental stage the metabolomic profile was affected by bud position and commercial treatment. Starch accumulated as long as buds remain closed; upon bud opening starch content declined. Reciprocally, sugar levels rose during flower opening and were affected by edge/ midrib location and commercial treatment. Glucose, fructose and sucrose levels remained higher in opened flowers still on the plant. AMY2 (amylase) transcript levels rose as did those of two sugar transporters (MST6 and SWEET7). Commercial processing therefore impacts on the metabolome and the ability to accumulate sugars in the opening flower bud. Commercial treatment delayed bud opening and the effect was dependent on the position of the bud on the stem. However, it had little impact on the rate of cell expansion during flower opening. Cell expansion in the different areas of the adaxial epidermis was unaffected by the commercial treatment. Furthermore, edge and adaxial tepal cells expanded faster during opening. Expression of cell expansion related genes (EXPA1 and LoPIP1) fell as flowers opened. This differential cell expansion in the tepal sectors could underpin the transition of a convex to a concave tepal shape during opening. In conclusion, commercial processing mainly affects the early stages of bud opening. Sugar and metabolite accumulation is compromised by commercial treatment, but this did not affect the capacity for cell expansion in the tepal. Furthermore, our data indicate that differential cell expansion in the different sectors of the tepals is important in lily flower opening, and that this is associated with starch breakdown and sugar accumulation

Genome-wide characterization and expression of two-component system genes in cytokinin-regulated gall formation in Zizania latifolia

The thickening of Zizania latifolia shoots, referred to as gall formation, depends on infection with the fungal endophyte Ustilago esculenta. The swollen and juicy shoots are a popular vegetable in Asia. A key role for cytokinin action in this process was postulated. Here, trans-zeatin stimulated swelling in fungi-infected Z. latifolia. A two-component system (TCS) linked cytokinin binding to receptors with transcriptional regulation in the nucleus and played important roles in diverse biological processes. We characterized 69 TCS genes encoding for 25 histidine kinase/histidine-kinase-like (HK(L)) (21 HKs and 4 HKLs), 8 histidine phosphotransfer proteins (HP) (5 authentic and 3 pseudo), and 36 response regulators (RR; 14 type A, 14 type B, 2 type C, and 6 pseudo) in the genome of Z. latifolia. These TCS genes have a close phylogenetic relationship with their rice counterparts. Nineteen duplicated TCS gene pairs were found and the ratio of nonsynonymous to synonymous mutations indicated that a strong purifying selection acted on these duplicated genes, leading to few mutations during evolution. Finally, ZlCHK1, ZlRRA5, ZIRRA9, ZlRRA10, ZlPRR1, and ZlPHYA expression was associated with gall formation. Among them, ARR5, ARR9, and ZlPHYA are quickly induced by trans-zeatin, suggesting a role for cytokinin signaling in shoot swelling of Z. latifolia. Keywords: two-component system; Z. latifolia; shoot swelling; cytokinin signal

STM sustains stem cell function in the Arabidopsis shoot apical meristem and controls KNOX gene expression independently of the transcriptional repressor AS1

The Arabidopsis KNOX gene SHOOT MERISTEMLESS (STM) is required for both the development and the sustained function of the shoot apical meristem (SAM) and can induce de novo meristem formation when expressed ectopically. STM acts through induction of cytokinin (CK) synthesis to inhibit cellular differentiation and additionally functions to organize undifferentiated cells into a self-sustaining meristem. STM has been shown to positively regulate the related KNOX genes KNAT1/BP and KNAT2, and it has been proposed that this is mediated through repression of the ARP-type transcriptional repressor ASYMMETRIC LEAVES1 (AS1). Here we investigate the role of STM in SAM organization, stem cell maintenance and the regulation of KNOX gene expression. We show that culture of stm mutant explants in high CK conditions does not restore proper sustained shoot growth, supporting the idea of STM having CK-independent roles in meristem function. Furthermore, we show that STM is required for continued stem cell function in the SAM by sustaining expression of the stem cell-promoting factor WUS and preventing cells of the meristem organizing center from adopting lateral organ-specific fates. We also demonstrate that transcriptional activation of class-1 KNOX genes by STM is independent of AS1, since AS1 transcript levels are not reduced in response to STM and STM is able to transactivate expression of both KNAT1/BP and KNAT2 in the as1 mutant background

Unsupervised analysis of FLIM-FRET data

We have developed an unsupervised method to analyze fluorescence lifetime imaging microscopy data based on non-negative matrix factorization. Additionally, by modelling the Förster resonant energy transfer process between donor and acceptor fluorophores, we retrieve the dynamics and the distribution of donor-acceptor pairs

Seed size plasticity in response to embryonic lethality conferred by ectopic CYD activation is dependent on plant architecture

The size of seeds is the result of cell proliferation and growth in the three seed compartments: the embryo, endosperm and integuments. Targeting expression of the D-type cyclin CYCD7;1 to the central cell and early endosperm (FWA:CYCD7;1) triggered nuclear divisions and partial ovule abortion, reducing seed number in each silique and leading to increased seed size. A similar effect on seed size was observed with other segregating embryo lethal mutations, suggesting caution is needed in interpreting apparent seed size phenotypes. Here, we show that the positive effect of FWA:CYCD7;1 on Arabidopsis seed size is modulated by the architecture of the mother plant. Larger seeds were produced in FWA:CYCD7;1 lines with unmodified inflorescences, and also upon removal of side branches and axillary stems. This phenotype was absent from inflorescences with increased axillary floral stems produced by pruning of the main stem. Given this apparent confounding influence of resource allocation on transgenes effect, we conclude that plant architecture is a further important factor to consider in appraising seed phenotypes

Assessment of nutritional stress in famine burials using stable isotope analysis

YesObjectives: We compared δ15N and δ13C values from bone and dentine collagen profiles of individuals interred in famine‐related and attritional burials to evaluate whether individuals in medieval London who experienced nutritional stress exhibit enriched nitrogen in bone and tooth tissue. Dentine profiles were evaluated to identify patterns that may be indicative of famine during childhood and were compared with the age of enamel hypoplasia (EH) formation to assess whether isotopic patterns of undernutrition coincide with the timing of physiological stress. Materials and Methods: δ15N and δ13C isotope ratios of bone collagen were obtained from individuals (n = 128) interred in attritional and famine burials from a medieval London cemetery (c. 1120–1539). Temporal sequences of δ15N and δ13C isotope profiles for incrementally forming dentine collagen were obtained from a subset of these individuals (n = 21). Results: Results indicate that individuals from attritional graves exhibit significantly higher δ15N values but no significant differences were found between burial types for the sexes. Analyses of dentine profiles reveal that a lower proportion of famine burials exhibit stable dentine profiles and that several exhibit a pattern of opposing covariance between δ15N and δ13C. EH were also observed to have formed during or after the opposing covariance pattern for some individuals. Conclusions: The results of this study may reflect differences in diet between burial types rather than nutritional stress. Though nutritional stress could not be definitively identified using bone and dentine collagen, the results from dentine analysis support previous observations of biochemical patterns associated with nutritional stress during childhood.Division of Behavioral and Cognitive Sciences. Grant Numbers: BCS‐1261682, BCS‐1540208. Office of the Vice President for Research, University of South Carolina. Grant Number: SPARC Fellowship Gran