Deletion of a cyclin-dependent protein kinase inhibitor, CsSMR1, leads to dwarf and determinate growth in cucumber (Cucumis sativus L.)

Key message A 7.9 kb deletion which contains a cyclin-dependent protein kinase inhibitor leads to determinate growth and dwarf phenotype in cucumber. Abstract Plant architecture is a composite character which are mainly defined by shoot branching, internode elongation and shoot determinacy. Ideal architecture tends to increase the yield of plants, just like the case of “Green Revolution” increased by the application of semi-dwarf cereal crop varieties in 1960s. Cucumber (Cucumis sativus L.) is an important vegetable cultivated worldwide, and suitable architecture varieties were selected for different production systems. In this study, we obtained a novel dwarf mutant with strikingly shortened plant height and determinate growth habit. By bulked segregant analysis and map-based cloning, we delimited the dw2 locus to a 56.4 kb region which contain five genes. Among all the variations between WT and dw2 within the 56.4 kb region, a 7.9 kb deletion which resulted in complete deletion of CsaV3_5G035790 in dw2 was co-segregated with the dwarf phenotype. Haplotype analysis and gene expression analysis suggest that CsaV3_5G035790 encoding a cyclin-dependent protein kinase inhibitor (CsSMR1) be the candidate gene responsible for the dwarf phenotype in dw2. RNA-seq analysis shows that several kinesin-like proteins, cyclins and reported organ size regulators are expressed differentially between WT and dw2, which may account for the reduced organ size in dwarf plants. Additionally, the down-regulation of CsSTM and CsWOX9 in dw2 resulted in premature termination of shoot apical meristem development, which eventually reduces the internode number and plant height. Identification and characterization of the CsSMR1 provide a new insight into cucumber architecture modification to be applied to mechanized production system.

CHIQUITA1 maintains temporal transition between proliferation and differentiation in Arabidopsis thaliana

Body size varies widely among species, populations, and individuals depending on the environment. Transitioning between proliferation and differentiation is a crucial determinant of final organ size, but how the timing of this transition is established and maintained remains unknown. Using cell proliferation markers and genetic analysis, we show that CHIQUITA1 (CHIQ1) is required to maintain the timing of the transition from proliferation to differentiation in Arabidopsis thaliana. Combining kinematic and cell lineage tracking studies, we found that the number of actively dividing cells in chiquita1-1 plants decreases prematurely compared to wild type plants, suggesting CHIQ1 maintains the proliferative capacity in dividing cells and ensures that cells divide a certain number of times. CHIQ1 belongs to a plant-specific gene family of unknown molecular function and physically and genetically interacts with three close members of its family to control the timing of proliferation exit. Our work reveals the interdependency between cellular and organ-level processes underlying final organ size determination.

From spikes to intercellular waves: Tuning intercellular calcium signaling dynamics modulates organ size control

Information flow within and between cells depends significantly on calcium (Ca2+) signaling dynamics. However, the biophysical mechanisms that govern emergent patterns of Ca2+ signaling dynamics at the organ level remain elusive. Recent experimental studies in developing Drosophila wing imaginal discs demonstrate the emergence of four distinct patterns of Ca2+ activity: Ca2+ spikes, intercellular Ca2+ transients, tissue-level Ca2+ waves, and a global “fluttering” state. Here, we used a combination of computational modeling and experimental approaches to identify two different populations of cells within tissues that are connected by gap junction proteins. We term these two subpopulations “initiator cells,” defined by elevated levels of Phospholipase C (PLC) activity, and “standby cells,” which exhibit baseline activity. We found that the type and strength of hormonal stimulation and extent of gap junctional communication jointly determine the predominate class of Ca2+ signaling activity. Further, single-cell Ca2+ spikes are stimulated by insulin, while intercellular Ca2+ waves depend on Gαq activity. Our computational model successfully reproduces how the dynamics of Ca2+ transients varies during organ growth. Phenotypic analysis of perturbations to Gαq and insulin signaling support an integrated model of cytoplasmic Ca2+ as a dynamic reporter of overall tissue growth. Further, we show that perturbations to Ca2+ signaling tune the final size of organs. This work provides a platform to further study how organ size regulation emerges from the crosstalk between biochemical growth signals and heterogeneous cell signaling states.

PSXII-19 Organ and cellular contributions to heat production in Brahman and Angus steers

Reductions in basal metabolism and growth rate appear to contribute to decreased heat production of Bos indicus breeds. Lower metabolic rate may be due to smaller organ size and lower metabolic activity. Liver and heart account for high percentage of metabolic activity relative to their weight, and at a cellular level, mitochondria are responsible for producing energy for cellular maintenance. Our objective was to determine liver and heart weight and evaluate expression of key mitochondrial proteins in Bos indicus (80–100% Brahman) and Bos taurus (80–100% Angus) steers. Steers (n = 14 per breed) were harvested at the university meat laboratory. After evisceration, livers and hearts were weighed, and samples were frozen in liquid nitrogen for further analyses. Western blotting was used to determine expression of proteins in mitochondrial energy production: citrate synthase, a marker of mitochondria content; succinate dehydrogenase B (SDH-B), complex II; cytochrome c oxidase subunit IV, complex IV; and ATP synthase subunit 5A (ATP5A), complex V. Data were analyzed using an unpaired t-test in SAS-JMP. Although steers were similar age at slaughter (P = 0.84), Brahman steers weighed less (P < 0.0001) and thus produced lighter carcasses (P < 0.0001) and smaller livers and hearts (P < 0.0001). On a relative basis (kg organ/kg BW), Brahman tended to possess smaller hearts (P = 0.06) and smaller livers (P = 0.03). Expression of mitochondria proteins in heart did not differ between breeds (P > 0.3). However, Brahman exhibited lower expression of SDH-B (P = 0.005) but tended to have higher expression of ATP5A (P = 0.07) in liver. Altogether, this supports that smaller organ size is a contributing factor to lower heat production in heat-tolerant Brahman steers, and shifts in mitochondria protein expression in liver may impact energy metabolism at the cellular level.

The Putative Role of the NAC Transcription Factor EjNACL47 in Cell Enlargement of Loquat (Eriobotrya japonica Lindl.)

NAC transcription factors (TFs) are plant-specific TFs that play essential roles in plant development; however, the function of NAC TFs in loquat development remains unknown. The natural triploid loquat (Eriobotrya japonica Lindl.), Longquan No.1. B355, has larger organs than its corresponding diploid loquat (B2). Here, we cloned an NAC-like TF (EjNACL47 (NAC-like 47)) from the cDNA of triploid loquat B355 flowers. EjNACL47 has a conserved domain of NAC TFs and is homologous to AtNAC47. Transient expression in tobacco leaves revealed that EjNACL47 localized to the nucleus, and yeast-two-hybrid screening confirmed that the C-terminus displayed transcriptional activity. Interestingly, real-time qRT-PCR indicated that the expression levels of EjNACL47 in leaves and flower organs in triploid loquat (B355) were higher than those in diploid loquat (B2), implying that EjNACL47 might be associated with the larger organ size in B355. Moreover, Arabidopsis lines ectopically expressing EjNACL47 presented obviously larger leaves, flowers, and siliques than the wild-type variant, suggesting that EjNACL47 plays a positive role in Arabidopsis organ enlargement. These results offer insight into the molecular mechanism of NAC TFs involved in regulating organ size in loquat.

Is Plant Life-History of Biseasonal Germination Consistent in Response to Extreme Precipitation?

Future climate is projected to increase in the intensity and frequency of extreme precipitation events, and the resulting ecological consequences are often more serious than those of normal precipitation events. In particular, in desert ecosystems, due to the low frequency and strong fluctuation of extreme precipitation, the destructive consequences for desert plants caused by extreme precipitation have not received enough attention for some time. Based on statistics of extreme precipitation events (1965–2018) in the Gurbantunggut Desert, we investigated the effects of extreme precipitation (+0%, CK; +50%, W1; +100%, W2; +200%, W3; maintenance of field capacity, W4) on the plant life-history of the spring-germinated (SG) and autumn-germinated (AG) ephemeral plant Erodium oxyrhynchum by monitoring seedling emergence, survival, phenology, organ size, biomass accumulation, and allocation. The results showed that extreme precipitation caused about 2.5% seedling emergence of E. oxyrhynchum in autumn 2018 and 3.0% seedling emergence in early spring 2019, which means that most seeds may be stored in the soil or have died. Meanwhile, extreme precipitation significantly improved the survival, organ size, and biomass accumulation of SG and AG plants, and W3 was close to the precipitation threshold of SG (326.70 mm) and AG (560.10 mm) plants corresponding to the maximum individual biomass; thus, AG plants with a longer life cycle need more water for growth. Conversely, W4 caused AG plants to enter the leaf stage in advance and led to death in winter, which indicates that extreme precipitation may not be good for AG plants. Root and reproduction biomass allocation of SG and AG plants showed a significantly opposite trend under extreme precipitation treatments, which might be related to their different life-history strategies. Therefore, when only taking into account the changing trend of extreme precipitation from the Coupled Model Intercomparison Project 6 (CMIP6) climate projections data, we speculate that extreme precipitation may promote the growth of SG and AG plants from the beginning to the middle of this century, but extreme precipitation in autumn exceeding a certain threshold may adversely affect the survival of AG plants at the end of the century.