Molecular mechanisms of self-incompatibility in Brassicaceae and Solanaceae

Self-incompatibility (SI) is a mechanism for preventing self-fertilization in flowering plants. SI is controlled by a single S-locus with multiple haplotypes (S-haplotypes). When the pistil and pollen share the same S-haplotype, the pollen is recognized as self and rejected by the pistil. This review introduces our research on Brassicaceae and Solanaceae SI systems to identify the S-determinants encoded at the S-locus and uncover the mechanisms of self/nonself-discrimination and pollen rejection. The recognition mechanisms of SI systems differ between these families. A self-recognition system is adopted by Brassicaceae, whereas a collaborative nonself-recognition system is used by Solanaceae. Work by our group and subsequent studies indicate that plants have evolved diverse SI systems.

Dominance in self-compatibility between subgenomes of allopolyploid Arabidopsis kamchatica shown by transgenic restoration of self-incompatibility

The evolutionary transition to self-compatibility facilitates polyploid speciation. In Arabidopsis relatives, the self-incompatibility system is characterized by epigenetic dominance modifiers, among which small RNAs suppress the expression of a recessive SCR/SP11 haplogroup. Although the contribution of dominance to polyploid self-compatibility is speculated, little functional evidence has been reported. Here we employ transgenic techniques to the allotetraploid plant A. kamchatica. We find that when the dominant SCR-B is repaired by removing a transposable element insertion, self-incompatibility is restored. This suggests that SCR was responsible for the evolution of self-compatibility. By contrast, the reconstruction of recessive SCR-D cannot restore self-incompatibility. These data indicate that the insertion in SCR-B conferred dominant self-compatibility to A. kamchatica. Dominant self-compatibility supports the prediction that dominant mutations increasing selfing rate can pass through Haldane's sieve against recessive mutations. The dominance regulation between subgenomes inherited from progenitors contrasts with previous studies on novel epigenetic mutations at polyploidization termed genome shock.

SHI family transcription factors regulate an interspecific barrier

Pre-zygotic interspecies incompatibility in angiosperms is an important mechanism to prevent unfavourable hybrids between species. Here we report our identification of STIGMATIC PRIVACY 2 (SPRI2), a transcription factor that has a zinc-finger domain and regulates interspecies barriers in Arabidopsis thaliana, via genome-wide association study. Knockout analysis of SPRI2/SRS7 and its paralogue SPRI2-like/SRS5 demonstrated their necessity in rejecting male pollen from other species within female pistils. Additionally, they govern mRNA transcription of xylan O-acetyltransferases (TBL45 and TBL40) related to cell wall modification, alongside SPRI1, a pivotal transmembrane protein for interspecific pollen rejection. SPRI2/SRS7 is localized as condensed structures in the nucleus formed via liquid-liquid phase separation (LLPS), and a prion-like sequence in its amino-terminal region was found to be responsible for the formation of the condensates. The LLPS-regulated SPRI2/SRS7 discovered in this study may contribute to the establishment of interspecific reproductive barriers through the transcriptional regulation of cell wall modification genes and SPRI1.

Comprehensive computational analysis of the SRK-SP11 molecular interaction underlying self-incompatibility in Brassicaceae using improved structure prediction for cysteine-rich proteins

Plants employ self-incompatibility (SI) to promote cross-fertilization. In Brassicaceae, this process is regulated by the formation of a complex between the pistil determinant S receptor kinase (SRK) and the pollen determinant S-locus protein 11 (SP11, also known as S-locus cysteine-rich protein, SCR). In our previous study, we used the crystal structures of two eSRK-SP11 complexes in Brassica rapa S8 and S9 haplotypes and nine computationally predicted complex models to demonstrate that only the SRK ectodomain (eSRK) and SP11 pairs derived from the same S haplotype exhibit high binding free energy. However, predicting the eSRK-SP11 complex structures for the other 100 + S haplotypes and genera remains difficult because of SP11 polymorphism in sequence and structure. Although protein structure prediction using AlphaFold2 exhibits considerably high accuracy for most protein monomers and complexes, 46% of the predicted SP11 structures that we tested showed < 75 mean per-residue confidence score (pLDDT). Here, we demonstrate that the use of curated multiple sequence alignment (MSA) for cysteine-rich proteins significantly improved model accuracy for SP11 and eSRK-SP11 complexes. Additionally, we calculated the binding free energies of the predicted eSRK-SP11 complexes using molecular dynamics (MD) simulations and observed that some Arabidopsis haplotypes formed a binding mode that was critically different from that of B. rapa S8 and S9. Thus, our computational results provide insights into the haplotype-specific eSRK-SP11 binding modes in Brassicaceae at the residue level. The predicted models are freely available at Zenodo, https://doi.org/10.5281/zenodo.8047768.

MLPK function is not required for self-incompatibility in the S29 haplotype of Brassica rapa L

S²⁹ haplotype does not require the MLPK function for self-incompatibility in Brassica rapa. Self-incompatibility (SI) in Brassicaceae is regulated by the self-recognition mechanism, which is based on the S-haplotype-specific direct interaction of the pollen-derived ligand, SP11/SCR, and the stigma-side receptor, SRK. M locus protein kinase (MLPK) is known to be one of the positive effectors of the SI response. MLPK directly interacts with SRK, and is phosphorylated by SRK in Brassica rapa. In Brassicaceae, MLPK was demonstrated to be essential for SI in B. rapa and Brassica napus, whereas it is not essential for SI in Arabidopsis thaliana (with introduced SRK and SP11/SCR from related SI species). Little is known about what determines the need for MLPK in SI of Brassicaceae. In this study, we investigated the relationship between S-haplotype diversity and MLPK function by analyzing the SI phenotypes of different S haplotypes in a mlpk/mlpk mutant background. The results have clarified that in B. rapa, all the S haplotypes except the S²⁹ we tested need the MLPK function, but the S²⁹ haplotype does not require MLPK for the SI. Comparative analysis of MLPK-dependent and MLPK-independent S haplotype might provide new insight into the evolution of S-haplotype diversity and the molecular mechanism of SI in Brassicaceae.

Influences of smoking on central blood pressure in hypertensive subjects

Background/Introduction

Smoking is known to induce systemic vascular damage, leading to cardiovascular diseases. Recent studies demonstrated that central blood pressure has a greater impact on cardiovascular events than brachial blood pressure.

Purpose

We investigated influences of habitual smoking on central systolic blood pressure (CSBP) in hypertensive subjects.

Methods

A total of 5630 subjects (male = 2622, 51.7±12.0 year-old at baseline), who visited our hospital for a physical check-up at least twice during the last 10 years and underwent CSBP measurement at each visit, were enrolled, and they were divided into three groups; normotensive (n=4634), non-treated hypertensive (n=91) and treated hypertensive subjects (n=905). Then, the influences of smoking on the average and yearly changes of CSBP (median follow-up 5 years) were analyzed. Brachial blood pressure (oscillometer) and radial artery pressure waveforms (tonometer) were recorded using an automated device, and the pressure corresponding to the second systolic peak of radial pressure waveforms was taken as CSBP (HEM-9000AI, Omron Healthcare, Kyoto). Hypertension was defined as brachial BP ≥140/90mmHg or the use of antihypertensive medications. A yearly change in CSBP was calculated in each subject by linear regression analysis using longitudinal data.

Results

The average CSBP was higher in habitual smokers than in non-smokers when analyzed in normotensive (109.1±11.7 vs. 107.6±12.8 mmHg, p&lt;0.001) and non-treated hypertensive subjects (150.7±14.8 vs. 142.8±16.7 mmHg, p&lt;0.05), whereas in hypertensive subjects under medication the average CSBP was lower in smokers than in non-smokers (124.6±12.4 vs. 127.8±13.6 mmHg, p&lt;0.01). Smoking status did not affect yearly changes of CSBP in normotensive (habitual smokers vs. non-smokers; 1.38±6.00 vs. 1.44±6.04 mmHg/year), treated hypertensive (−0.16±7.08 vs. −0.66±8.24 mmHg/year), and non-treated hypertensive subjects (4.09±15.1 vs. −0.53±10.3 mmHg/year).

Conclusions

Habitual smoking increases CSBP, however, antihypertensive medications counteract the unfavorable effects of smoking on CSBP. These results imply a new pathway underlying the development of cardiovascular diseases in smokers. Unfavorable changes in the cardiovascular system caused by smoking may quite slowly progress that short period of observation in the present study could not have detected enhanced yearly increases of CSBP by smoking.

Funding Acknowledgement

Type of funding sources: None.

Relationship between year-to-year blood pressure variability and target organ damage in the general population

Background/Introduction

Visit-to-visit blood pressure variability (BPV) is a strong predictor of cardiovascular events as well as target organ damage (TOD) in hypertension. However, effects of year-to-year BPV on the development of TOD have not been investigated in the general population.

Purpose

The present study was designed to investigate a possible relationship between year-to-year BPV and TOD in the general population.

Methods

Consecutive 5542 subjects (male=3771, 58.6±10.7 yea-old) who visited our hospital for an annual physical check-up for 5 years in a row during 2008 and 2013 were enrolled. The average, standard deviation (SD), coefficient of variation (CV), and average real variability (ARV) of systolic blood pressure (SBP) were calculated using data during the period. Other baseline data were obtained in 2013; left ventricular hypertrophy (LVH; Sokolow-Lyon voltage &gt;3.8 mV and/or Cornell product &gt;2440 mm ms) and kidney impairment (estimated glomerular filtration rate; eGFR&lt;60) were taken as TOD. Then, subjects without TOD at baseline (2013) (n=3801, male=2584, 57.4±10.4 yea-old) were followed up until 2019 (median = 5 years) and the impact of BPV on the development of TOD was investigated.

Results

The average, SD, CV and ARV of SBP were 123.8 mmHg, 8.04 mmHg, 6.50%, and 9.19 mmHg, respectively. At baseline, these parameters were higher in subjects with TOD than those without TOD (Table 1-A). During the follow-up of subjects without TOD at baseline, LVH and kidney impairment developed in 425 and 623 subjects (24.7 and 35.8 per 1000 person-year), respectively. In retrospective analysis, the average, SD, and ARV were higher in subjects with than without future TOD (Table 1-B). Although some indices of year-to-year BPV predicted future development of TOD in univariate Cox-hazard analysis, only the average of SBP predicted incident TOD after adjustment.

Conclusions

Year-to-year BPV is a marker of the incident TOD in the general population. However, these indices do not independently predict the onset of TOD and, thus, there may be unknown pathway that links TOD and BPV.

Funding Acknowledgement

Type of funding sources: None. Table 1. BP variability and TODTable 2. Cox-hazard analyses

Spatiogenetic characterization of S receptor kinase (SRK) alleles in naturalized populations of Raphanus sativus L. var. raphanistroides on Yakushima island

In various coastal areas of Japan, naturalized radish populations are observed. Radish is a cruciferous plant and exhibits self-incompatibility, involving a system controlled by a single locus with multiple S alleles. Although the S allele diversity of radish cultivars and wild radishes has been characterized, the S allele distribution in naturalized populations has not yet been analyzed in relation to the positions of the plants in situ. Here, we show the S allele distribution in naturalized radish populations of Yakushima, a small island in the East China Sea, with positions of the plants. Radish plants were sampled in coastal areas in Yakushima, and their S alleles were detected and characterized. Most of the S alleles had been previously identified in radish cultivars. However, four novel S alleles, which may be unique to Yakushima, were also found. Moreover, seeds in siliques from plants growing in the study areas were sampled, and S allele determination in DNA extracted from these seeds suggested that the plants had exchanged their pollen among their close neighbors. There was also a problem in that the PCR amplification of some SRK alleles was difficult because of their sequence diversity in the naturalized populations, as occurs in cultivars. Our results suggest that the exchange of S alleles between cultivars and naturalized populations occurs and that S alleles in naturalized populations are highly diverse. The methodology established in our study should be applicable to other self-incompatible species to dissect the diversity of S allele distribution in naturalized populations.

Two aquaporins, SIP1;1 and PIP1;2, mediate water transport for pollen hydration in the Arabidopsis pistil

Pollination is the crucial initial step that brings together the male and female gametophytes, and occurs at the surface of the stigmatic papilla cell in Arabidopsis thaliana. After pollen recognition, pollen hydration is initiated as a second critical step to activate desiccated mature pollen grains for germination, and thus water transport from pistil to pollen is essential for this process. In this study, we report a novel aquaporin-mediated water transport process in the papilla cell as a control mechanism for pollen hydration. Coupled with a time-series imaging analysis of pollination and a reverse genetic analysis using T-DNA insertion Arabidopsis mutants, we found that two aquaporins, the ER-bound SIP1;1 and the plasma membrane-bound PIP1;2, are key players in water transport from papilla cell to pollen during pollination. In wild type plant, hydration speed reached its maximal value within 5 min after pollination, remained high until 10-15 min. In contrast, sip1;1 and pip1;2 mutants showed no rapid increase of hydration speed, but instead a moderate increase during ∼25 min after pollination. Pollen of sip1;1 and pip1;2 mutants had normal viability without any functional defects for pollination, indicating that decelerated pollen hydration is due to a functional defect on the female side in sip1;1 and pip1;2 mutants. In addition, sip1;1 pip1;2 double knockout mutant showed a similar impairment of pollen hydration to individual single mutants, suggesting that their coordinated regulation is critical for proper water transport, in terms of speed and amount, in the pistil to accomplish successful pollen hydration.

Effect of advancing age on dietary salt intakes: a 10-year follow-up study

Background/Introduction

The National Nutrition Survey in Japan indicated that dietary salt intake of the Japanese is gradually decreasing for the last several decades, while salt intakes are higher in elderly than young people. There is no survey on the alteration of salt intakes with advancing age in individuals.

Purpose

The present study investigated effects of aging on salt intakes in individuals.

Methods

A total of 2600 subjects (men; 1787, age; 30 to 79 years-old at 2008) who participated in our physical check-up program both in 2008 and 2018 were enrolled. Individual dietary salt intakes in 2008 and 2018, which were estimated using a spot urine by a previously reported method, were compared.

Results

The mean age and salt intakes at 2008 were 53.9±10.0 years and 12.2±3.2 g/day in men and 54.4±9.2 years and 8.3±2.1 g/day in women, respectively. Salt intake increased to 13.2±3.3 g/day in men and 8.8±2.2 g/day in women during the 10 years. Salt intakes were higher in hypertensive than normotensive subjects both at 2008 and 2018, but changes of blood pressure category were not associated with those of salt intakes during the 10 years (table). Changes in salt intakes in each decade are shown in Figure. Salt intakes in each decade increased with advancing age both in men and women until their 70s. Salt intakes in people in their 60s and 70s at 2018 were higher than those at 2008. Similar results were obtained in subjects without any anti-hypertensive medications (n=1667) (data not shown).

Conclusions

The observational follow-up study revealed that salt intakes in each individual increased after the interval of 10 years in both men and women. The results suggest that the sense of taste changes with advancing age in young adults as well as elderly persons, which may be related with alterations of lifestyle.

Age difference in changes of salt intake

Funding Acknowledgement

Type of funding source: None

What is the optimal blood pressure level for kidney in the general population?

Background/Introduction

Hypertension induces kidney dysfunction, and vice versa. Furthermore, kidney dysfunction can be a risk factor for cardiovascular diseases as well as end-stage of kidney disease. Although blood pressure (BP) control is necessary to prevent deterioration of kidney function, strict BP control may deteriorate kidney function.

Purpose

The present observational study investigated effects of BP levels on the incidence of chronic kidney disease (CKD) in the general population.

Methods

A total of 12,753 subjects with normal kidney function (estimated glomerular filtration rate [eGFR] ≥60 mL/min per 1.73 m2) (male 7,707, mean age 51.8 years) who visited our hospital for an annual physical check-up from April 2010 to March 2018 were enrolled. After baseline examination, subjects were followed up until March 2019 (median 1769 days) with the endpoint being the development of CKD (eGFR&lt;60 mL/min per 1.73 m2). The modified MDRD formula for Japanese was used to calculate eGFR. Hypertension was defined as BP ≥140/90mmHg or the use of antihypertensive medication.

Results

During the follow-up period, 1,604 subjects developed CKD (26.9 per 1,000 person-years) with the incidence being more frequent in hypertensive (n=3,098) than normotensive (n=9,655) subjects at enrollment (44.2 vs. 21.5 per 1,000 person-years, respectively; hazard ratio [95% confidence interval] from multivariate Cox proportional analysis 1.205 [1.061–1.369]). Hazard ratio of systolic BP at baseline was 1.006 [1.002–1.010] in a multivariate Cox proportional hazard regression model adjusted for possible risk factors. The incidence was lower in subjects without hypertension throughout the follow-up period (normotension group, n=7,866) than those who were diagnosed as having hypertension at least once during the period (hypertension group, n=4,887) (23.1 vs. 32.3 per 1,000 person-years, p&lt;0.001). In the normotension group, subjects with average BP &lt;120/80mmHg had lower incidence of CKD than in those with BP ≥120/80mmHg (17.2 vs. 36.1 per 1,000 person-years, p&lt;0.001). In contrast, in the hypertension group, the incidences of CKD in subjects with average BP &lt;120/80, 120–139/80–89 and ≥140/90mmHg were 34.3, 25.8, and 54.4 per 1,000 person-years, respectively (p&lt;0.001). Moreover, in hypertensive subjects under medication (n=2,002) with average BP &lt;120/80, 120–139/80–89 and ≥140/90mmHg, the incidence of CKD was 65.5, 41.3, and 64.3 per 1,000 person-years, respectively (p&lt;0.01).

Conclusions

The incidence of CKD was higher in hypertensive than in normotensive subjects. The lower BP was associated with the lower incidence of CKD in normotensive subjects, while strict BP control may increase the risk of CKD in hypertensive subjects.

Funding Acknowledgement

Type of funding source: None

Excessive salt intake is a significant predictor for future development of metabolic syndrome in the general population

Background/Introduction

Dietary salt consumption is one of the most important modifiable factors in our lifestyle and restriction of dietary salt results in the reduction of blood pressure in previous studies. Excessive salt intake causes cardiovascular diseases independently of its effects on blood pressure. Since metabolic syndrome also increases a risk of cardiovascular disease, there may be some association between salt intake and metabolic syndrome.

Purpose

The present study was designed to investigate a possible relationship between salt intake and future development of metabolic syndrome in the general population.

Methods

Consecutive 12,256 subjects without metabolic syndrome (male=7,053, 52.1±12.3 year-old) who visited our hospital for an annual physical check-up from April 2010 to March 2018 were enrolled. After baseline examination, subjects were followed up until March 2019 (median 1,582 days) with the endpoint being the development of metabolic syndrome. Metabolic syndrome was diagnosed according to the Japanese criteria (2005). Individual salt intake was estimated using a spot urine by a previously reported method.

Results

Salt intake was 11.9±3.0 g/day in male and 8.2±2.1 g/day in female subjects at baseline. During the follow-up period, 1,669 subjects developed metabolic syndrome (29.9 per 1,000 person-year) with the incidence being more frequent in male than female subjects (41.8 vs. 14.2 per 1,000 person-year). Non-adjusted hazard ratio (HR) (95% confidence interval [CI]) of salt intake for the development of metabolic syndrome was 1.157 (1.142–1.173). In analysis where subjects were divided into gender-specific quartiles according to the baseline salt intake, Kaplan-Meyer curve analysis revealed that the incidence of metabolic syndrome were increased across the quartiles (20.6, 25.0, 32.4, and 42.7 per 1,000 person-years; logrank p&lt;0.001). Multivariate Cox proportional hazard analysis adjusted for age, gender, body mass index, systolic blood pressure, heart rate, serum creatinine, uric acid, fasting plasma glucose, low-density lipoprotein cholesterol, triglyceride, hemoglobin and current smoking habit at baseline revealed that salt intake predicted the new onset of metabolic syndrome (HR: 1.036, 95% CI: 1.019–1.054).

Conclusions

Excessive salt intake is significantly associated with the new development of metabolic syndrome in the general population. The results suggest that salt restriction prevents metabolic syndrome as well as hypertension leading to cardiovascular diseases.

Funding Acknowledgement

Type of funding source: None

Mechanism of self/nonself-discrimination in Brassica self-incompatibility

Self-incompatibility (SI) is a breeding system that promotes cross-fertilization. In Brassica, pollen rejection is induced by a haplotype-specific interaction between pistil determinant SRK (S receptor kinase) and pollen determinant SP11 (S-locus Protein 11, also named SCR) from the S-locus. Although the structure of the B. rapa S₉-SRK ectodomain (eSRK) and S₉-SP11 complex has been determined, it remains unclear how SRK discriminates self- and nonself-SP11. Here, we uncover the detailed mechanism of self/nonself-discrimination in Brassica SI by determining the S₈-eSRK-S₈-SP11 crystal structure and performing molecular dynamics (MD) simulations. Comprehensive binding analysis of eSRK and SP11 structures reveals that the binding free energies are most stable for cognate eSRK-SP11 combinations. Residue-based contribution analysis suggests that the modes of eSRK-SP11 interactions differ between intra- and inter-subgroup (a group of phylogenetically neighboring haplotypes) combinations. Our data establish a model of self/nonself-discrimination in Brassica SI.

Double-Locking Mechanism of Self-Compatibility in Arabidopsis thaliana: The Synergistic Effect of Transcriptional Depression and Disruption of Coding Region in the Male Specificity Gene

Self-compatibility in Arabidopsis thaliana represents the relatively recent disruption of ancestral obligate cross pollination, recognized as one of the prevalent evolutionary pathways in flowering plants, as noted by Darwin. Our previous study found that inversion of the male specificity gene (SP11/SCR) disrupted self-incompatibility, which was restored by overexpressing the SCR with the reversed inversion. However, SCR in A. thaliana has other mutations aside from the pivotal inversion, in both promoter and coding regions, with probable effects on transcriptional regulation. To examine the functional consequences of these mutations, we conducted reciprocal introductions of native promoters and downstream sequences from orthologous loci of self-compatible A. thaliana and self-incompatible A. halleri. Use of this inter-species pair enabled us to expand the scope of the analysis to transcriptional regulation and deletion in the intron, in addition to inversion in the native genomic background. Initial analysis revealed that A. thaliana has a significantly lower basal expression level of SCR transcripts in the critical reproductive stage compared to that of A. halleri, suggesting that the promoter was attenuated in inducing transcription in A. thaliana. However, in reciprocal transgenic experiments, this A. thaliana promoter was able to restore partial function if coupled with the functional A. halleri coding sequence, despite extensive alterations due to the self-compatible mode of reproduction in A. thaliana. This represents a synergistic effect of the promoter and the inversion resulting in fixation of self-compatibility, primarily enforced by disruption of SCR. Our findings elucidate the functional and evolutionary context of the historical transition in A. thaliana thus contributing to the understanding of the molecular events leading to development of self-compatibility.

Dioctatin Activates ClpP to Degrade Mitochondrial Components and Inhibits Aflatoxin Production

Aflatoxin contamination of crops is a serious problem worldwide. Utilization of aflatoxin production inhibitors is attractive, as the elucidation of their modes of action contributes to clarifying the mechanism of aflatoxin production. Here, we identified mitochondrial protease ClpP as the target of dioctatin, an inhibitor of aflatoxin production of Aspergillus flavus. Dioctatin conferred uncontrolled caseinolytic capacity on ClpP of A. flavus and Escherichia coli. Dioctatin-bound ClpP selectively degraded mitochondrial energy-related proteins in vitro, including a subunit of respiratory chain complex V, which was also reduced by dioctatin in a ClpP-dependent manner in vivo. Dioctatin enhanced glycolysis and alcohol fermentation while reducing tricarboxylic acid cycle metabolites. These disturbances were accompanied by reduced histone acetylation and reduced expression of aflatoxin biosynthetic genes. Our results suggest that dioctatin inhibits aflatoxin production by inducing ClpP-mediated degradation of mitochondrial energy-related components, and that mitochondrial energy metabolism functions as a key determinant of aflatoxin production.

Characterization of self-incompatible Brassica napus lines lacking SP11 expression

Recognition of self-incompatibility (SI) is regulated by the SRK and SP11 genes in Brassicaceae. Brassica rapa and B. oleracea are self-incompatible, while most cultivated species of B. napus, which arose from hybridization between B. rapa and B. oleracea, are self-compatible. Various studies of the SRK and SP11 genes in self-compatible B. napus have been reported, but details of the mechanism in different B. napus lines are not fully understood. In this study, we confirmed the S haplotypes, SI phenotypes and SP11 expression in 10 representative lines of B. napus, and identified two SI lines (N110 and N343) lacking SP11 expression. In N343 (with BnS¹ and BnS⁶ haplotypes), we confirmed that there is a 3.6-kb insertion in the promoter region of BnSP11-1, and that BnSP11-1 and BnSP11-6 are not expressed, as reported previously (expression of BnSP11-6 is suppressed by the BnS¹ haplotype), although this line is self-incompatible. Similarly, in N110, with two novel S haplotypes (BnS⁸ and BnS⁹) in addition to BnS⁶, a 4.3-kb insertion was identified in the promoter region of BnSP11-9, and expression levels of BnSP11-6, BnSP11-8 and BnSP11-9 were all suppressed (BnSP11-6 and BnSP11-8 may be suppressed by BnS⁸ and BnS⁹, respectively), although the phenotype was self-incompatible. This observation of an SI phenotype without SP11 expression suggests the existence of unknown factor(s) that induce pollen-stigma incompatibility in B. napus.

Genetic and tissue-specific RNA-sequencing analysis of self-compatible mutant TSC28 in Brassica rapa L. toward identification of a novel self-incompatibility factor

Self-incompatibility (SI) is a sophisticated system for pollen selectivity to prevent pollination by genetically identical pollen. In Brassica, it is genetically controlled by a single, highly polymorphic S-locus, and the male and female S-determinant factors have been identified as S-locus protein 11 (SP11)/S-locus cysteine-rich protein (SCR) and S-locus receptor kinase (SRK), respectively. However, the overall molecular system and identity of factors in the downstream cascade of the SI reaction remain unclear. Previously, we identified a self-compatible B. rapa mutant line, TSC28, which has a disruption in an unidentified novel factor of the SI signaling cascade. Here, in a genetic analysis of TSC28, using an F₂ population from a cross with the reference B. rapa SI line Chiifu-401, the causal gene was mapped to a genetic region of DNA containing markers BrSA64 and ACMP297 in B. rapa chromosome A1. By fine mapping using an F₂ population of 1,034 plants, it was narrowed down to a genetic region between DNA markers ACMP297 and BrgMS4028, with physical length approximately 1.01 Mbp. In this genomic region, 113 genes are known to be located and, among these, we identified 55 genes that were expressed in the papilla cells. These are candidates for the gene responsible for the disruption of SI in TSC28. This list of candidate genes will contribute to the discovery of a novel downstream factor in the SP11-SRK signaling cascade in the Brassica SI system.

A stigmatic gene confers interspecies incompatibility in the Brassicaceae

Pre-zygotic interspecies incompatibility in angiosperms is a male-female relationship that inhibits the formation of hybrids between two species. Here, we report on the identification of STIGMATIC PRIVACY 1 (SPRI1), an interspecies barrier gene in Arabidopsis thaliana. We show that the rejection activity of this stigma-specific plasma membrane protein is effective against distantly related Brassicaceae pollen tubes and is independent of self-incompatibility. Point-mutation experiments and functional tests of synthesized hypothetical ancestral forms of SPRI1 suggest evolutionary decay of SPRI1-controlled interspecies incompatibility in self-compatible A. thaliana. Hetero-pollination experiments indicate that SPRI1 ensures intraspecific fertilization in the pistil when pollen from other species are present. Our study supports the idea that SPRI1 functions as a barrier mechanism that permits entrance of pollen with an intrinsic signal from self species.

Improvement of infrared imaging video bolometer for application to deuterium experiment on the large helical device

An infrared imaging video bolometer was improved for application to a neutron environment in fusion plasma devices, i.e., the Large Helical Device (LHD). In order to calibrate the thermal characteristics of the activated foil absorber inside the plasma vacuum vessel, the remote-controlled in situ calibration system was improved with high-surface-flatness mirrors. Furthermore, the carbon coating method was improved by introducing a vacuum evaporation technique instead of the conventional spray technique to realize the coating on both sides of the absorber with reproducibility and uniformity. The optimal thickness of the coating was also determined. Owing to these coating improvements, the reproducibility of the effective emissivity on both sides especially was improved. Finally, the variation with the neutron irradiation of the thermal characteristics of the foil absorber was investigated. It was found that the effect was not significant for the total neutron emission of 3.6 × 10¹⁸ on LHD.

Multilayered dominance hierarchy in plant self-incompatibility

Epigenetic dominance modifier. In polymorphic loci, complex genetic dominance relationships between alleles are often observed. In plants, control of self-incompatibility (SI) expression via allelic interactions in the Brassicaceae is the best-known example of such mechanisms. Here, with emphasis on two recently published papers, we review the progress toward understanding the dominance regulatory mechanism of SI in the Brassicaceae. Multiple small RNA genes linked to the Self-incompatibility (S) locus were found in both Brassica and Arabidopsis genera. Mono-allelic gene expression of the male determinant of SI, SP11/SCR, from a dominant S-allele is under epigenetic control by such small RNA genes. Possible evolutionary trajectories leading to the formation of multilayered dominance hierarchy in Brassicaceae are discussed. We also identify some remaining questions for future studies.

Duplicated pollen-pistil recognition loci control intraspecific unilateral incompatibility in Brassica rapa

In plants, cell-cell recognition is a crucial step in the selection of optimal pairs of gametes to achieve successful propagation of progeny. Flowering plants have evolved various genetic mechanisms, mediated by cell-cell recognition, to enable their pistils to reject self-pollen, thus preventing inbreeding and the consequent reduced fitness of progeny (self-incompatibility, SI), and to reject foreign pollen from other species, thus maintaining species identity (interspecific incompatibility)¹. In the genus Brassica, the SI system is regulated by an S-haplotype-specific interaction between a stigma-expressed female receptor (S receptor kinase, SRK) and a tapetum cell-expressed male ligand (S locus protein 11, SP11), encoded by their respective polymorphic genes at the S locus^2-6. However, the molecular mechanism for recognition of foreign pollen, leading to reproductive incompatibility, has not yet been identified. Here, we show that recognition between a novel pair of proteins, a pistil receptor SUI1 (STIGMATIC UNILATERAL INCOMPATIBILITY 1) and a pollen ligand PUI1 (POLLEN UNILATERAL INCOMPATIBILITY 1), triggers unilateral reproductive incompatibility between plants of two geographically distant self-incompatible Brassica rapa lines, even though crosses would be predicted to be compatible based on the S haplotypes of pollen and stigma. Interestingly, SUI1 and PUI1 are similar to the SI genes, SRK and SP11, respectively, and are maintained as cryptic incompatibility genes in these two populations. The duplication of the SRK and SP11 followed by reciprocal loss in different populations would provide a molecular mechanism of the emergence of a reproductive barrier in allopatry.

Structure of the SHR-SCR heterodimer bound to the BIRD/IDD transcriptional factor JKD

The plant-specific GAI, RGA and SCR (GRAS) family proteins play critical roles in plant development and signalling. Two GRAS proteins, SHORT-ROOT (SHR) and SCARECROW (SCR), cooperatively direct asymmetric cell division and the patterning of root cell types by transcriptional control in conjunction with BIRD/INDETERMINATE DOMAIN (IDD) transcription factors, although precise details of these specific interactions and actions remain unknown. Here, we present the crystal structures of the SHR-SCR binary and JACKDAW (JKD)/IDD10-SHR-SCR ternary complexes. Each GRAS domain comprises one α/β core subdomain with an α-helical cap that mediates heterodimerization by forming an intermolecular helix bundle. The α/β core subdomain of SHR forms the BIRD binding groove, which specifically recognizes the zinc fingers of JKD. We identified a conserved SHR-binding motif in 13 BIRD/IDD transcription factors. Our results establish a structural basis for GRAS-GRAS and GRAS-BIRD interactions and provide valuable clues towards our understanding of these regulators, which are involved in plant-specific signalling networks.

New insights into mammalian signaling pathways using microfluidic pulsatile inputs and mathematical modeling

Temporally modulated input mimics physiology. This chemical communication strategy filters the biochemical noise through entrainment and phase-locking. Under laboratory conditions, it also expands the observability space for downstream responses. A combined approach involving microfluidic pulsatile stimulation and mathematical modeling has led to deciphering of hidden/unknown temporal motifs in several mammalian signaling pathways and has provided mechanistic insights, including how these motifs combine to form distinct band-pass filters and govern fate regulation under dynamic microenvironment. This approach can be utilized to understand signaling circuit architectures and to gain mechanistic insights for several other signaling systems. Potential applications include synthetic biology and biotechnology, in developing pharmaceutical interventions, and in developing lab-on-chip models.

The Shape of the Triangular Fibrocartilage During Pronation–Supination

We studied the changes in the shape of the triangular fibrocatilage (TFC: disc proper) which occur during forearm rotation in disarticulated and articulated wrists. The influence of artificial 3 mm ulnar lengthening on distortion of the disc was also examined. In the disarticulated wrists, slight distortion of the central and radial portions of the TFC was observed in the ulnar neutral variance specimens. More distortion was noted in the radial and central portions of the TFC in specimens with positive ulnar variance or with the ulna lengthened. However, in the articulated wrist, the TFC demonstrated little change in shape during pronosupination even in the ulnar positive variance wrists or with the ulna lengthened. There was no significant change in palmar and dorsal peripheral lengths of the TFC in ulnar neutral, ulnar positive or ulna-lengthened specimens at three rotatory positions of the forearm. These findings suggest that changes in ulnar variance which occur during forearm rotation can produce distortion on the TFC, but the carpus helps to maintain the shape of the TFC during pronation–supination, even with positive ulnar variance.

A complex dominance hierarchy is controlled by polymorphism of small RNAs and their targets

In diploid organisms, phenotypic traits are often biased by effects known as Mendelian dominant-recessive interactions between inherited alleles. Phenotypic expression of SP11 alleles, which encodes the male determinants of self-incompatibility in Brassica rapa, is governed by a complex dominance hierarchy^1-3. Here, we show that a single polymorphic 24 nucleotide small RNA, named SP11 methylation inducer 2 (Smi2), controls the linear dominance hierarchy of the four SP11 alleles (S₄₄ > S₆₀ > S₄₀ > S₂₉). In all dominant-recessive interactions, small RNA variants derived from the linked region of dominant SP11 alleles exhibited high sequence similarity to the promoter regions of recessive SP11 alleles and acted in trans to epigenetically silence their expression. Together with our previous study⁴, we propose a new model: sequence similarity between polymorphic small RNAs and their target regulates mono-allelic gene expression, which explains the entire five-phased linear dominance hierarchy of the SP11 phenotypic expression in Brassica.

MYB transcription factor gene involved in sex determination in Asparagus officinalis

Dioecy is a plant mating system in which individuals of a species are either male or female. Although many flowering plants evolved independently from hermaphroditism to dioecy, the molecular mechanism underlying this transition remains largely unknown. Sex determination in the dioecious plant Asparagus officinalis is controlled by X and Y chromosomes; the male and female karyotypes are XY and XX, respectively. Transcriptome analysis of A. officinalis buds showed that a MYB-like gene, Male Specific Expression 1 (MSE1), is specifically expressed in males. MSE1 exhibits tight linkage with the Y chromosome, specific expression in early anther development and loss of function on the X chromosome. Knockout of the MSE1 orthologue in Arabidopsis induces male sterility. Thus, MSE1 acts in sex determination in A. officinalis.

In situ calibration of the foil detector for an infrared imaging video bolometer using a carbon evaporation technique

The InfraRed imaging Video Bolometer (IRVB) is a useful diagnostic for the multi-dimensional measurement of plasma radiation profiles. For the application of IRVB measurement to the neutron environment in fusion plasma devices such as the Large Helical Device (LHD), in situ calibration of the thermal characteristics of the foil detector is required. Laser irradiation tests of sample foils show that the reproducibility and uniformity of the carbon coating for the foil were improved using a vacuum evaporation method. Also, the principle of the in situ calibration system was justified.

Cullin1-P is an Essential Component of Non-Self Recognition System in Self-Incompatibility in Petunia

Self-incompatibility (SI) in flowering plants is a genetic reproductive barrier to distinguish self- and non-self pollen to promote outbreeding. In Solanaceae, self-pollen is rejected by the ribonucleases expressed in the styles (S-RNases), via its cytotoxic function. On the other side, the male-determinant is the S-locus F-box proteins (SLFs) expressed in pollen. Multiple SLFs collaboratively detoxify non-self S-RNases, therefore, non-self recognition is the mode of self-/non-self discrimination in Solanaceae. It is considered that SLFs function as a substrate-recognition module of the Skp1-Cullin1-F-box (SCF) complex that inactivates non-self S-RNases via their polyubiquitination, which leads to degradation by 26S proteasome. In fact, PhSSK1 (Petunia hybrida SLF-interacting Skp1-like1) was identified as a specific component of SCF^SLF and was shown to be essential for detoxification of S-RNase in Petunia However, different molecules are proposed as the candidate Cullin1, another component of SCF^SLF, and there is as yet no definite conclusion. Here, we identified five Cullin1s from the expressed sequence tags (ESTs) derived from the male reproductive organ in Petunia Among them, only PhCUL1-P was co-immunoprecipitated with S₇-SLF2. In vitro protein-binding assay suggested that PhSSK1 specifically forms a complex with PhCUL1-P in an SLF-dependent manner. Knockdown of PhCUL1-P suppressed fertility of transgenic pollen in cross-compatible pollination in the functional S-RNase-dependent manner. These results suggested that SCF^SLF selectively uses PhCUL1-P. Phylogeny of Cullin1s indicates that CUL1-P is recruited into the SI machinery during the evolution of Solanaceae, suggesting that the SI components have evolved differently among species in Solanaceae and Rosaceae, despite both families sharing the S-RNase-based SI.

Identification of reference genes for quantitative expression analysis using large-scale RNA-seq data of Arabidopsis thaliana and model crop plants

In quantitative gene expression analysis, normalization using a reference gene as an internal control is frequently performed for appropriate interpretation of the results. Efforts have been devoted to exploring superior novel reference genes using microarray transcriptomic data and to evaluating commonly used reference genes by targeting analysis. However, because the number of specifically detectable genes is totally dependent on probe design in the microarray analysis, exploration using microarray data may miss some of the best choices for the reference genes. Recently emerging RNA sequencing (RNA-seq) provides an ideal resource for comprehensive exploration of reference genes since this method is capable of detecting all expressed genes, in principle including even unknown genes. We report the results of a comprehensive exploration of reference genes using public RNA-seq data from plants such as Arabidopsis thaliana (Arabidopsis), Glycine max (soybean), Solanum lycopersicum (tomato) and Oryza sativa (rice). To select reference genes suitable for the broadest experimental conditions possible, candidates were surveyed by the following four steps: (1) evaluation of the basal expression level of each gene in each experiment; (2) evaluation of the expression stability of each gene in each experiment; (3) evaluation of the expression stability of each gene across the experiments; and (4) selection of top-ranked genes, after ranking according to the number of experiments in which the gene was expressed stably. Employing this procedure, 13, 10, 12 and 21 top candidates for reference genes were proposed in Arabidopsis, soybean, tomato and rice, respectively. Microarray expression data confirmed that the expression of the proposed reference genes under broad experimental conditions was more stable than that of commonly used reference genes. These novel reference genes will be useful for analyzing gene expression profiles across experiments carried out under various experimental conditions.

Non-self- and self-recognition models in plant self-incompatibility

The mechanisms by which flowering plants choose their mating partners have interested researchers for a long time. Recent findings on the molecular mechanisms of non-self-recognition in some plant species have provided new insights into self-incompatibility (SI), the trait used by a wide range of plant species to avoid self-fertilization and promote outcrossing. In this Review, we compare the known SI systems, which can be largely classified into non-self- or self-recognition systems with respect to their molecular mechanisms, their evolutionary histories and their modes of evolution. We review previous controversies on haplotype evolution in the gametophytic SI system of Solanaceae species in light of a recently elucidated non-self-recognition model. In non-self-recognition SI systems, the transition from self-compatibility (SC) to SI may be more common than previously thought. Reversible transition between SI and SC in plants may have contributed to their adaptation to diverse and fluctuating environments.