Transitions between self-compatibility and self-incompatibility and the evolution of reproductive isolation in the large and diverse tropical genus Dendrobium (Orchidaceae)

Background and Aims The evolution of interspecific reproductive barriers is crucial to understanding species evolution. This study examines the contribution of transitions between self-compatibility (SC) and self-incompatibility (SI) and genetic divergence in the evolution of reproductive barriers in Dendrobium, one of the largest orchid genera. Specifically, it investigates the evolution of pre- and postzygotic isolation and the effects of transitions between compatibility states on interspecific reproductive isolation within the genus.Methods The role of SC and SI changes in reproductive compatibility among species was examined using fruit set and seed viability data available in the literature from 86 species and ∼2500 hand pollinations. The evolution of SC and SI in Dendrobium species was investigated within a phylogenetic framework using internal transcribed spacer sequences available in GenBank.Key Results Based on data from crossing experiments, estimations of genetic distance and the results of a literature survey, it was found that changes in SC and SI significantly influenced the compatibility between species in interspecific crosses. The number of fruits produced was significantly higher in crosses in which self-incompatible species acted as pollen donor for self-compatible species, following the SI × SC rule. Maximum likelihood and Bayesian tests did not reject transitions from SI to SC and from SC to SI across the Dendrobium phylogeny. In addition, postzygotic isolation (embryo mortality) was found to evolve gradually with genetic divergence, in agreement with previous results observed for other plant species, including orchids.Conclusions Transitions between SC and SI and the gradual accumulation of genetic incompatibilities affecting postzygotic isolation are important mechanisms preventing gene flow among Dendrobium species, and may constitute important evolutionary processes contributing to the high levels of species diversity in this tropical orchid group.     

Genetic diversity and structure in two species of Leavenworthia with self-incompatible and self-compatible populations

Self-fertilization is a common mating system in plants and is known to reduce genetic diversity, increase genetic structure and potentially put populations at greater risk of extinction. In this study, we measured the genetic diversity and structure of two cedar glade endemic species, Leavenworthia alabamica and L. crassa. These species have self-incompatible (SI) and self-compatible (SC) populations and are therefore ideal for understanding how the mating system affects genetic diversity and structure. We found that L. alabamica and L. crassa had high species-level genetic diversity (H_e=0.229 and 0.183, respectively) and high genetic structure among their populations (F_ST=0.45 and 0.36, respectively), but that mean genetic diversity was significantly lower in SC compared with SI populations (SC vs SI, H_e for L. alabamica was 0.065 vs 0.206 and for L. crassa was 0.084 vs 0.189). We also found significant genetic structure using maximum-likelihood clustering methods. These data indicate that the loss of SI leads to the loss of genetic diversity within populations. In addition, we examined genetic distance relationships between SI and SC populations to analyze possible population history and origins of self-compatibility. We find there may have been multiple origins of self-compatibility in L. alabamica and L. crassa. However, further work is required to test this hypothesis. Finally, given their high genetic structure and that individual populations harbor unique alleles, conservation strategies seeking to maximize species-level genetic diversity for these or similar species should protect multiple populations.     

Evolutionary origin of the Asteraceae capitulum: Insights from Calyceraceae

? Premise of the study: Phylogenies based on molecular data are revealing that generalizations about complex morphological structures often obscure variation and developmental patterns important for understanding the evolution of forms, as is the case for inflorescence morphology within the well-supported MGCA clade (Menyanthaceae + Goodeniaceae + Calyceraceae + Asteraceae). While the basal families share a basic thyrsic/thyrsoid structure of their inflorescences, Asteraceae possesses a capitulum that is widely interpreted as a racemose, condensed inflorescence. Elucidating the poorly known inflorescence structure of Calyceraceae, sister to Asteraceae, should help clarify how the Asteraceae capitulum evolved from thyrsic/thyrsoid inflorescences. ? Methods: The early development and structure of the inflorescence of eight species (five genera) of Calyceraceae were studied by SEM, and patterns of evolutionary change were interpreted via phylogenetic character mapping. ? Key results: The basic inflorescence structure of Calyceraceae is a cephalioid (a very condensed botryoid/thyrsoid). Optimization of inflorescence characters on a DNA sequence-derived tree suggests that the Asteraceae capitulum derives from a simple cephalioid through two morphological changes: loss of the terminal flower and suppression of the cymose branching pattern in the peripheral branches. ? Conclusions: Widely understood as a condensed raceme, the Asteraceae capitulum is the evolutionary result of a very reduced, condensed thyrsoid. Starting from that point, evolution worked separately only on the racemose developmental control/pattern within Asteraceae and mainly on the cymose developmental control/pattern within Calyceraceae, producing head-like inflorescences in both groups but with very different diversification potential. We also discuss possible remnants of the ancestral cephalioid structure in some Asteraceae.     

EXAMINING TWO STANDARD ASSUMPTIONS OF ANCESTRAL RECONSTRUCTIONS: REPEATED LOSS OF DICHROMATISM IN DABBLING DUCKS (ANATINI)

Although phylogenetic reconstruction of ancestral character states is becoming an increasingly common technique for studying evolution, few researchers have assessed the reliability of these reconstructions. Here I test for congruence between a phylogenetic reconstruction and a widely accepted scenario based on independent lines of evidence. I used Livezey's (1991) phylogeny to reconstruct ancestral states of plumage dichromatism in dabbling ducks (Anatini). Character state mapping reconstructs monochromatic ancestors for the genus Anas as well as most of its main clades. This reconstruction differs strongly from the widely accepted scenario of speciation and plumage evolution in the group (e.g., Delacour and Mayr 1945; Sibley 1957). This incongruence may occur because two standard assumptions of character state reconstruction are probably not met in this case. Violating either of these two assumptions would be a source of error sufficient to create misleading reconstructions. The first assumption that probably does not apply to ducks is that terminal taxa, in this case species, are monophyletic. Many of the widespread dichromatic species of ducks may be paraphyletic and ancestral to isolated monochromatic species. Three lines of evidence support this scenario: population-level phylogenies, biogeography, and vestigial plumage patterns. The second assumption that probably does not apply to duck plumage color is that gains and losses of character states are equally likely. Four lines of evidence suggest that dichromatic plumage might be lost more easily than gained: weak female preferences for bright male plumage, biases toward the loss of sexually dichromatic characters, biases toward the loss of complex characters, and repeated loss of dichromatism in other groups of birds. These seven lines of evidence support the accepted scenario that widespread dichromatic species repeatedly budded off isolated monochromatic species. Drift and genetic biases probably caused the easy loss of dichromatism in ducks and other birds during peripatric speciation. In order to recover the accepted scenario using Livezey's tree, losses of dichromatism must be five times more likely than gains. The results of this study caution against the uncritical use of unordered parsimony as the sole criterion for inferring ancestral states. Detailed population-level sampling is needed and altered transformation weighting may be warranted in ducks and in many other groups and character types with similar attributes.     

SRK-SCR转基因拟南芥自交不亲和性的研究进展

十字花科植物自交不亲和性（SI）受墨位点（S-locus）编码的sRK和sCR控制,它们分别是柱头和花粉中的sI特异识别因子。野生型拟南芥不具有sI,而近来通过转基因手段将外源艘K—scR基因转入野生型拟南芥可以使其表现sI,由此建立了一个可用于十字花科sI研究的新型模式植物。本文综述了利用这种转基因拟南芥在SI机制及进化方面取得的进展,包括sI新基因的挖掘、候选基因功能分析和拟南芥生殖模式的转变等。     

Disentangling the components of pollen limitation in a widespread herb with gametophytic self-incompatibility

Premise

Seed production is frequently limited by the receipt of insufficient or low-quality pollen, collectively termed “pollen limitation” (PL). In taxa with gametophytic self-incompatibility (GSI), incompatible pollen can germinate on stigmas but pollen tubes are arrested in styles. This allows for estimates of pollen performance before, during, and after self-recognition, as well as insight into the factors underlying pollen quality limitation in GSI taxa.

Methods

We scored pollen performance following self and outcross pollinations in Argentina anserina to identify the location of self-recognition and establish the relationship between pollen tubes and seed production. We then estimated quantity and quality components of PL from >3300 field-collected styles. We combined our results with other studies to test the prediction that low pollen quality, but not quantity, drives higher PL in self-incompatible (SI) taxa than in self-compatible taxa (SC).

Results

Self and outcross pollen germinated readily on stigmas, but 96% of germinated self-pollen was arrested during early tube elongation. Reproduction in the field was more limited by pollen quality than by quantity, and pollen failure near the location of self-recognition was a stronger barrier to fertilization than pollen germination. Across 26 taxa, SI species experienced stronger pollen quality, but not quantity, limitation than SC species.

Conclusions

Evaluating pollen performance at multiple points within pistils can elucidate potential causes of pollen quality limitation. The receipt of incompatible pollen inhibits fertilization success more than insufficient pollen receipt or poor pollen germination in A. anserina. Likewise, pollen quality limitation drives high overall PL in other SI taxa.     

The divergence history of the perennial plant Linaria cavanillesii confirms a recent loss of self‐incompatibility

Many angiosperms prevent inbreeding through a self‐incompatibility (SI) system, but the loss of SI has been frequent in their evolutionary history. The loss of SI may often lead to an increase in the selfing rate, with the purging of inbreeding depression and the ultimate evolution of a selfing syndrome, where plants have smaller flowers with reduced pollen and nectar production. In this study, we used approximate Bayesian computation (ABC) to estimate the timing of divergence between populations of the plant Linaria cavanillesii that differ in SI status and in which SI is associated with low inbreeding depression but not with a transition to full selfing or a selfing syndrome. Our analysis suggests that the mixed‐mating self‐compatible (SC) population may have begun to diverge from the SI populations around 2810 generation ago, a period perhaps too short for the evolution of a selfing syndrome. We conjecture that the SC population of L. cavanillesii is at an intermediate stage of transition between outcrossing and selfing.     

Ancestral state reconstruction of body size in the Caniformia (Carnivora, Mammalia): the effects of incorporating data from the fossil record

A recent molecular phylogeny of the mammalian order Carnivora implied large body size as the ancestral condition for the caniform subclade Arctoidea using the distribution of species mean body sizes among living taxa. "Extant taxa-only" approaches such as these discount character state observations for fossil members of living clades and completely ignore data from extinct lineages. To more rigorously reconstruct body sizes of ancestral forms within the Caniformia, body size and first appearance data were collected for 149 extant and 367 extinct taxa. Body sizes were reconstructed for four ancestral nodes using weighted squared-change parsimony on log-transformed body mass data. Reconstructions based on extant taxa alone favored large body sizes (on the order of 10 to 50 kg) for the last common ancestors of both the Caniformia and Arctoidea. In contrast, reconstructions incorporating fossil data support small body sizes (< 5 kg) for the ancestors of those clades. When the temporal information associated with fossil data was discarded, body size reconstructions became ambiguous, demonstrating that incorporating both character state and temporal information from fossil taxa unambiguously supports a small ancestral body size, thereby falsifying hypotheses derived from extant taxa alone. Body size reconstructions for Caniformia, Arctoidea, and Musteloidea were not sensitive to potential errors introduced by uncertainty in the position of extinct lineages relative to the molecular topology, or to missing body size data for extinct members of an entire major clade (the aquatic Pinnipedia). Incorporating character state observations and temporal information from the fossil record into hypothesis testing has a significant impact on the ability to reconstruct ancestral characters and constrains the range of potential hypotheses of character evolution. Fossil data here provide the evidence to reliably document trends of both increasing and decreasing body size in several caniform clades. More generally, including fossils in such analyses incorporates evidence of directional trends, thereby yielding more reliable ancestral character state reconstructions.     

Self-sterility in flowering plants: preventing self-fertilization increases family diversification rates

Background and Scope

New data are presented on the distribution and frequency of self-sterility (SS) – predominantly pre-zygotic self-incompatibility (SI) systems – in flowering plants and the hypothesis is tested that families with self-sterile taxa have higher net diversification rates (DRs) than those with exclusively self-compatible taxa using both absolute and relative rate tests.

Key Results

Three major forms of SI systems (where pollen is rejected at the stigmatic, stylar or ovarian interface) are found to occur in the oldest families of flowering plants, with times of divergence >100 million years before the present (mybp), while post-fertilization SS and heterostyly appear in families with crown ages of 81 and 87 mybp, respectively. It is also founnd that many (22) angiosperm families exhibit >1 SI phenotype and that the distribution of different types of SS does not show strong phylogenetic clustering, collectively suggesting that SS and SI systems have evolved repeatedly de novo in angiosperm history. Families bearing self-sterile taxa have higher absolute DRs using all available calibrations of the angiosperm tree, and this affect is caused mostly by the high DR of families with homomorphic SI systems (in particular stigmatic SI) or those in which multiple SS/SI phenotypes have been observed (polymorphic). Lastly, using sister comparisons, it is further demonstrated that in 29 of 38 sister pairs (including 95 families), the self-sterile sister group had higher species richness and DR than its self-compatible sister based on either the total number of taxa in the clade with SS or only the estimated fraction to harbour SS based on literature surveys.

Conclusions

Collectively, these analyses point to the importance of SS, particularly pre-zygotic SI in the evolution of flowering plants.     

Out of Gondwanaland; the evolutionary history of cooperative breeding and social behaviour among crows, magpies, jays and allies

Cooperative breeding is comparatively rare among birds in the mainly temperate and boreal Northern Hemisphere. Here we test if the distribution of breeding systems reflects a response to latitude by means of a phylogenetic analysis using correlates with geographical range among the corvids (crows, jays, magpies and allied groups). The corvids trace their ancestry to the predominantly cooperative 'Corvida' branch of oscine passerines from the Australo-Papuan region on the ancient Gondwanaland supercontinent, but we could not confirm the ancestral state of the breeding system within the family, while family cohesion may be ancestral. Initial diversification among pair-breeding taxa that are basal in the corvid phylogeny, represented by genera such as Pyrrhocorax and Dendrocitta, indicates that the corvid family in its current form could have evolved from pair-breeding ancestors only after they had escaped the Australo-Papuan shield. Within the family, cooperative breeding (alloparental care/family cohesion) is strongly correlated to latitude and its predominance in species maintaining a southerly distribution indicates a secondary evolution of cooperative breeding in the lineage leading away from the basal corvids. Multiple transitions show plasticity in the breeding system, indicating a response to latitude rather than evolutionary inertia. The evolutionary background to the loss of cooperative breeding among species with a northerly distribution is complex and differs between species, indicating a response to a variety of selection forces. Family cohesion where the offspring provide alloparental care is a main route to cooperatively breeding groups among corvids. Some corvid species lost only alloparental care, while maintaining coherent family groups. Other species lost family cohesion and, as a corollary, they also lost the behaviour where retained offspring provide alloparental care.     

A new genetic locus for self-compatibility in the outcrossing grass species perennial ryegrass (Lolium perenne)

BackgroundSelf-incompatibility (SI) is a physiological mechanism that many flowering plants employ to prevent self-fertilization and maintain heterozygosity. In the grass family this is known to be controlled by a two locus (S-Z) system; however, the SI system is intrinsically leaky. Modifier genes of both the S and Z loci and a further locus, T, are known to override SI leading to self-fertilization and self-seed production. This has implications for the ecological and evolutionary success as well as the commercial breeding of grasses. Here we report a study where the genetic control of self-compatibility (SC) was determined from the results of self-pollinating an F₂ population of perennial ryegrass from two independently derived inbred lines produced by single-seed descent.Methods In vitro self-pollinations of 73 fertile plants were analysed. A genetic association analysis was made with a panel of 1863 single-nucleotide polymorphism (SNP) markers, generated through genotype-by-sequencing methodology. Markers were placed on a recombination map of seven linkage groups (LGs) created using Joinmap v.5. The seed set on self- and open-pollinated inflorescences was determined on 143 plants, including the 73 plants analysed for self-pollination response.Key ResultsSelf-pollinations revealed a bimodal distribution of percentage SC with peaks at 50 and 100 %. A single quantitative trait locus (QTL) was identified with peak association for marker 6S14665z17875_11873 that mapped to LG 6. Peak position was associated with maximum marker segregation distortion. The self-compatible plants were equally fecund after self- and open pollination.ConclusionsThis is the first report in the Poaceae family of an SC locus located on LG 6. This new SC QTL discovery, as well as indicating the complex nature of the pollen–stigma recognition process and its evolutionary significance, provides an additional source of SC for breeding perennial ryegrass.     

Adaptive significance of self-fertilization in a hermaphroditic perennial, Trillium camschatcense (Melanthiaceae)

The evolution of self-fertilization from primarily outcrossing ancestors is one of the most common evolutionary transitions in plants; however, the ecological mechanisms that maintain self-fertilization have remained controversial. Theoretical studies suggest that selfing is advantageous over outcrossing in terms of genetic transmission and assurance of seed production under pollen-limited circumstances. Trillium camschatcense is a herbaceous perennial distributed in Hokkaido and northern Honshu, Japan. Geographical variation in the breeding system (self-compatible, SC; or self-incompatible, SI) has been reported in populations in Hokkaido. Here, we used several SC and SI populations of T. camschatcense to investigate the adaptive significance and the evolutionary basis of self-fertilization. Pollination experiments and genetic analyses demonstrated that the potential availability of outcross pollen in SC populations was sufficient and that the number of pollen donors was equal to that of SI populations. However, despite the high availability of outcross pollen, the SC populations produced seeds predominantly by selfing and so underwent severe inbreeding depression. Although none of the suggested advantages for self-fertilization were supported by our analyses, we propose two possible scenarios for the evolution of self-fertilization in T. camschatcense.     

Moving to mate: the evolution of separate and combined sexes in multicellular organisms

Which conditions favour the evolution of hermaphroditism or separate sexes? One classical hypothesis states that an organism’s mode of locomotion (if any) when searching for a mate should influence breeding system evolution. We used published phylogenies to reconstruct evolutionary changes in adult mate‐search efficiency and breeding systems among multicellular organisms. Employing maximum‐likelihood analyses, we found that changes in adult mate‐search efficiency are significantly correlated with changes in breeding system, and this result is robust to uncertainties in the phylogenies. These data provide the first statistical support, across a broad range of taxa, for the hypothesis that breeding systems and mate‐search efficiency did not evolve independently. We discuss our results in context with other causal factors, such as inbreeding avoidance and sexual specialization, likely to affect breeding system evolution.     

Characterization and practical use of self-compatibility in outcrossing grass species

BackgroundSelf-incompatibility (SI) systems prevent self-fertilization in several species of Poaceae, many of which are economically important forage, bioenergy and turf grasses. Self-incompatibility ensures cross-pollination and genetic diversity but restricts the ability to fix useful genetic variation. In most inbred crops it is possible to develop high-performing homozygous parental lines by self-pollination, which then enables the creation of F₁ hybrid varieties with higher performance, a phenomenon known as heterosis. The inability to fully exploit heterosis in outcrossing grasses is partially responsible for lower levels of improvement in breeding programmes compared with inbred crops. However, SI can be overcome in forage grasses to create self-compatible populations. This is generating interest in understanding the genetical basis of self-compatibility (SC), its significance for reproductive strategies and its exploitation for crop improvement, especially in the context of F₁ hybrid breeding.ScopeWe review the literature on SI and SC in outcrossing grass species. We review the currently available genomic tools and approaches used to discover and characterize novel SC sources. We discuss opportunities barely explored for outcrossing grasses that SC facilitates. Specifically, we discuss strategies for wide SC introgression in the context of the Lolium–Festuca complex and the use of SC to develop immortalized mapping populations for the dissection of a wide range of agronomically important traits. The germplasm available is a valuable practical resource and will aid understanding the basis of inbreeding depression and hybrid vigour in key temperate forage grass species.ConclusionsA better understanding of the genetic control of additional SC loci offers new insight into SI systems, their evolutionary origins and their reproductive significance. Heterozygous outcrossing grass species that can be readily selfed facilitate studies of heterosis. Moreover, SC introduction into a range of grass species will enable heterosis to be exploited in innovative ways in genetic improvement programmes.     

Independent origins of self-compatibility in Arabidopsis thaliana

The evolution from outcrossing based on self-incompatibility (SI) to a selfing system is one of the most prevalent transitions in flowering plants. It has been suggested that the loss of SI in Arabidopsis thaliana is associated with pseudogene formation at the SCR male component of the S locus. Recent work, however, suggests that alternative alleles with large deletions at the S locus are also present and may be responsible for the evolution of self-compatibility in this species. We demonstrate that most of these deletion alleles are evolutionarily derived from an S haplotype (haplogroups A) that already possessed the SCR pseudogene. This haplotype and its deletion variants are nearly fixed in Europe. Together with previous transgenic data, these results suggest that the pseudogenization of PsiSCR1 gene changed the SI phenotype in the majority of A. thaliana accessions, and was a critical step in the evolution of selfing in this species. Two other haplogroups (B and C) were also identified, the former of which contains a novel and possibly functional SCR allele. In contrast to haplogroups A, these two haplogroups are found primarily in Africa and Asia. These results suggest that self-compatibility, which appears to be fixed in this species, arose multiple times with different genetic bases, and indicates that a species-specific trait is associated with parallel evolution at the molecular level.     

RNaseI from Escherichia coli cannot substitute for S-RNase in rejection of Nicotiana plumbaginifolia pollen

Unilateral incompatibility often occurs between self-incompatible (SI) species and their self-compatible (SC) relatives. For example, SI Nicotiana alata rejects pollen from SC N. plumbaginifolia, but the reciprocal pollination is compatible. This interspecific pollen rejection system closely resembles intraspecific S-allele-specific pollen rejection. However, the two systems differ in degree of specificity. In SI, rejection is S-allele-specific, meaning that only a single S-RNase causes rejection of pollen with a specific S genotype. Rejection of N. plumbaginifolia pollen is less specific, occurring in response to almost any S-RNase. Here, we have tested whether a non-S-RNase can cause rejection of N. plumbaginifolia pollen. The Escherichia coli rna gene encoding RNaseI was engineered for expression in transgenic (N. plumbaginifolia × SC N. alata) hybrids. Expression levels and pollination behavior of hybrids expressing E. coli RNaseI were compared to controls expressing S_A2-RNase from N. alata. Immunoblot analysis and RNase activity assays showed that RNaseI and S_A2-RNase were expressed at comparable levels. However, expression of S_A2-RNase caused rejection of N. plumbaginifolia pollen, whereas expression of RNaseI did not. Thus, in this system, RNase activity alone is not sufficient for rejection of N. plumbaginifolia pollen. The results suggest that S-RNases may be specially adapted to function in pollen rejection.     

Breeding systems of Bromeliaceae species: evolution of selfing in the context of sympatric occurrence

Co-occurring congener plant species in the highly diverse Atlantic forests of southeastern Brazil may act as natural laboratories for evaluating evolution of reproductive shifts. We assessed the breeding systems in a sympatric assemblage of bromeliad species and compiled literature available for the family to compare our experiments with available information. We performed controlled experiments of autonomous selfing, self- and cross-pollination in 40 species of 11 genera of two subfamilies that, in general, overlap their blooming period and share the same pollination vectors. We also tested for differences between self-compatible (SC) and self-incompatible (SI) species with regard to ecological factors such as abundance, co-flowering and co-occurrence. Most species experimentally tested and surveyed in the literature (75%) were SC. Species from the subfamily Tillandsioideae were predominantly SC, while Bromelioideae showed greater variation in breeding systems. About 43% of the species studied set fruits spontaneously in the absence of pollinator vectors. We found that SC species were the more abundant, were more frequently associated with other relatives and overlapped their blooming period with other species more than SI species. Thus, our results suggest that self-compatibility is common for Bromeliaceae and do not support the traditional hypothesis of reproductive assurance used to explain the evolution of selfing. We discuss self-compatibility as a reproductive isolating mechanism in the presence of pollen flow among sympatric congener species.     

Phylogeny of Leavenworthia S-alleles suggests unidirectional mating system evolution and enhanced positive selection following an ancient population bottleneck

The adoption of self-fertilization from an ancestral outcrossing state is one of the most common evolutionary transitions in the flowering plants. In the mustard family, outcrossing is typically enforced by sporophytic self-incompatibility (SI), but there are also many self-compatible species. The genus Leavenworthia contains taxa that either possess or lack SI. Here, we present data showing that SI is associated with strict outcrossing and that there is widespread trans-specific sequence polymorphism at the locus involved in the recognition of self-pollen (the S-locus). This ancestral polymorphism is consistent with the presence of an outcrossing mating system in the common ancestor of Leavenworthia species, and suggests that there have been several independent losses of SI in the group. When compared with other mustard species, the bulk of Leavenworthia S-allele sequences are highly diverged from those found in other Brassicaceae and show relatively low levels of nucleotide diversity, a pattern that suggests the common ancestor of the genus likely underwent a strong population bottleneck. The hypothesis of postbottleneck S-locus rediversification is supported by tests showing stronger positive selection acting on S-alleles from Leavenworthia than those found in other Brassicaceae.