花色对吸引传粉者具有非常重要的作用。自然界的花色具有多样性,主要包括色调和着色模式的变异。虽然前人对花色变异的物质和遗传基础做了大量的研究,但许多花色变异模式特别是着色模式的分子机制还不清楚。传粉者与非传粉者因素介导的自然选择对花色表型变异的选择机制也有许多未解之谜。本文主要对已知花色表型变异的分子机制及自然选择对花色表型的选择作用进行综述,以便进一步地探索花色多样性存在的机制和自然选择对花色进化方向的影响。 Flower color plays a key role in attracting pollinators, and a staggering variety of flower color variations including color parameters and pigmentation pattern exist in nature. Though many studies have been done on the molecular mechanisms of flower color variation, there is still much unknown, especially for pigmentation pattern. The contributions of pollinator and non-pollinator agents to natural selection on floral color variation are also unclear. The review discusses recent data on genetic mechanisms and natural selection of flower color variation. The summary may as-sist us to further analyze molecular mechanisms of flower color diversity and role of natural se-lection in flower color variation.
张瑞娟1,2,鲁迎青1*
1中国科学院植物研究所系统与进化植物学国家重点实验室,北京
2中国科学院大学,北京
收稿日期:2016年11月8日;录用日期:2016年11月27日;发布日期:2016年11月30日
花色对吸引传粉者具有非常重要的作用。自然界的花色具有多样性,主要包括色调和着色模式的变异。虽然前人对花色变异的物质和遗传基础做了大量的研究,但许多花色变异模式特别是着色模式的分子机制还不清楚。传粉者与非传粉者因素介导的自然选择对花色表型变异的选择机制也有许多未解之谜。本文主要对已知花色表型变异的分子机制及自然选择对花色表型的选择作用进行综述,以便进一步地探索花色多样性存在的机制和自然选择对花色进化方向的影响。
关键词 :花青素,花色变异,传粉者,适合度,自然选择
花部性状特别是花色在吸引传粉者方面起着非常重要的作用。花色的呈现具有一定的遗传基础,且需要环境的参与。植物生理生化环境和花青素代谢途径上结构或调控基因的突变均可能带来花色表型的变异。自然界花色表型具有多样性,主要体现在花色参数和着色模式上。但许多花色变异模式的存在机理还不清楚,花色变异与自然选择之间的关系也需要深入研究。本文就花色呈现的生理生化基础、已知的花色变异遗传机制和传粉者及非传粉介质(如基因多效性、环境因子、病原菌、啃食者等)对花色进化的影响进行总结,以利于探讨花色多样性存在的机制。
花色呈现物质主要有三大类:甜菜碱(betalains)、类胡萝卜素(carotenoids)和类黄酮(flavonoids) [
花青素的合成是研究比较清楚的一个次生代谢通路(图1) [
图1. 花青素代谢途径(修改自[
和丙二酰辅酶A(malonyl-CoA)为底物,由结构基因(CHS、CHI、F3H、F3’H、F3’5’H、DFR和ANS)编码的一系列酶催化合成,并经糖基化、甲基化和酰基化等修饰后被转运至液泡中。其中F3H、F3’H和F3’5’H为花青素代谢途径的三个分支酶,其合成产物分别对应于天竺葵素、矢车菊素和飞燕草素。这些酶基因在许多植物中均已被克隆 [
已知花青素代谢途径由MYB、碱性螺旋–环–螺旋(bHLH)和WD40重复蛋白(WDR)三类调控因子主要以MBW三元复合物的形式调控 [
但一些MYB可单独起作用。如在玉米(Zea mays)中,P1(subgroup7)可单独激活花青素合成的一部分基因(CHS, CHI, DFR, FLS)而促进玉米粒中鞣酐(phlobaphene)的合成 [
花色表型多样性不仅体现在花色参数上,多样的着色模式(图2)更加丰富了花色的多态。这些变异可
图2.已报道的花色着色模式类型
能有利于增加植物的环境适应性。花色的变异具有一定的遗传基础,花青素代谢途径上结构或调控基因的突变(包括编码区和调控区)都或多或少会影响基因的功能或表达量而影响花色,基因的组织特异性表达或功能分化也会影响花色表型。
花青素代谢为类黄酮的一个代谢分支,根据类黄酮类物质和代谢途径基因类似片段的存在与否,人们推断类黄酮代谢途径应该起源于植物登陆 [
花色从蓝/紫色到红/粉色的变异通常是由于花青素从飞燕草素或矢车菊素到天竺葵素的转变,即花青素羟基数目的减少,因而常伴随羟基化酶基因F3’H或F3’5’H的功能失活或表达量降低(表2)。牵牛花仅含有矢车菊素和天竺葵素 [
物种名 | 基因名 | 突变形式 | 表型变异 | 参考文献 |
---|---|---|---|---|
Mimulus aurantiacus ssp. puniceus | MaMYB2 | Higher expression (CIS) | Yellow to red | [ |
M. luteus ssp. cupreus | PLA1 (R2R3-MYB) | ? | Yellow to orange red | [ |
M. luteus ssp. variegatus | PLA2 (R2R3-MYB) | ? | Yellow to purple | [ |
M. cardinalis | ROI1 (R3-MYB) | Lower expression (CIS or Trans) | Light pink to dark red | [ |
Phlox drummondii | R2R3-MYB | Higher expression (CIS) | Light blue to dark red | [ |
Antirrhinum majus ssp. Pseudomajus | ROSEAel | Gain of an activator (?) | Light yellow to dark red | [ |
A. majus ssp. Majus | ROSEAel | Gain of an activator (?) | Light yellow to dark red | [ |
表1. 花色获得的基因突变形式
COD代表编码区的突变;CIS代表cis调控区的突变;Trans代表反式作用转录因子的改变;“?”代表原因不详。
物种名 | 基因名 | 突变形式 | 表型变异 | 参考文献 |
---|---|---|---|---|
Ipomoea purpurea | F3'H | 550-bp Tip201 insertion in exon3 (COD) | Blue to pink | [ |
I. purpurea | F3'H | 402-bp DNA sequences insertion in exon3 (COD) | Blue to pink | [ |
I. nil | F3'H | C to T mutation in exon3 (COD) | Blue to pink | [ |
I. tricolor | F3'H | T insertion in exon2 (COD) | Blue to pink | [ |
I. quamoclit | F3'H | Lower expression in flower (CIS and tissue specific regulatory) | Blue to red | [ |
DFR-B | 15,3,3,6-bp in-frame and 98-bp DNA sequences insertion in 3'-flanking; Substrate specificity change (COD) | |||
I. horsfalliae | F3'H | Lower expression in flower (CIS and tissue specific regulatory) | Blue to red | [ |
I. coccinea | F3'H | Lower expression in flower (CIS and tissue specific regulatory) | Blue to red | [ |
Iochrominae.gesnerioides | F3'H | Lower expression in flower (CIS and tissue specific regulatory) | Blue to red | [ |
F3'5'H | A premature stop condon in exon1 and a 136-bp out-of-frame deletion in exon2 (COD) | |||
DFR-B | Substrate specificity change (COD) | |||
Penstemon barbatus | F3'H | Lower expression in flower (Tissue specific regulatory) | Blue to red | [ |
F3'5'H | A premature stop condon at amino acid 407; 11 nonsynonymous mutations (COD) | |||
P. labrosus | F3'5'H | Low activity on DHK and very low activity on DHQ | Blue to red | [ |
P. subulatus | F3'5'H | No activity on DHK and very low activity on DHQ | Blue to red | [ |
Penstemon (10 species) | F3'5'H | Two or more premature stop codons, large deletions, or frameshifting indels (COD) | Blue to red | [ |
Phlox drummondii | F3'5'H | Lower expression (CIS) | Blue to red | [ |
Petunia hybrida | F3'5'H | A Spm-like transposon (Psl) insertion in exon2 (COD) | Blue to red | [ |
P. hybrida | F3'5'H | Transposon insertion in exon3 (COD) | Blue to red | [ |
Gentiana scabra | F3'5'H | Two independent transposons insertion in exon1 (COD) | Blue to pink | [ |
Antirrhinum majus | F3'5'H | Lose of function (COD) | Blue to red | [ |
Glycine max | FLS | Single base deletion in coding region (COD) | Purple to magenta | [ |
表2. 花色由蓝/紫色到红/粉色变化的基因突变形式
COD代表编码区的突变;CIS代表cis调控区的突变;Trans代表反式作用转录因子的改变;“?”代表原因不详。
裂叶牵牛(I. nil)、三色牵牛(I. tricolor)而言,其红/粉色变异通常是由于F3’H的编码区突变造成 [
由于F3’H或F3’5’H分支被阻断,花青素代谢通路只能走F3H-DFR的路径,所以花色从蓝/紫色到红/粉色的变异有时还伴随着DFR底物特异性的改变,即对底物DHK亲和性的提高,对DHQ和DHM亲和性的降低 [
花色从蓝/紫/红色到白/黄色的变异通常被认为是花青素从有到无的变异,是质的变化。这些变化可能来自花青素代谢途径一个或多个步骤的阻断(表3)。代谢通路上结构基因的转座子插入 [
花青素量的变化可能与花青素代谢途径基因的表达量变化有关,但具体机制还不清楚。在亚洲百合(Asiatic hybrid lilies Lilium spp.)中,MYB12的表达量与花瓣中花青素的积累量呈正比 [
花的着色式样主要有断色、彩斑、缘环、星状、紫外模式、斑点、脉色和芽红等(图2)。目前已知的花色着色模式成因主要有四种:病毒感染、转座子的插入及部分回复突变、siRNA介导的基因转录后沉默、基因特别是调控基因的时空特异性表达(表4)。黄水仙花(Narcissus pseudonarcissus)由于水仙花叶病毒的感染会产生断色现象 [
物种名 | 基因名 | 突变形式 | 表型变异 | 参考文献 |
---|---|---|---|---|
Ipomoea purpurea | CHS-D | One copy of 3.9-kb Tip100 insertion in intron (COD) | Purple to white, flaked | [ |
I. purpurea | CHS-D | Two copies of Tip100 insertion in intron (COD) | Purple to stable white | [ |
I. purpurea | CHS-D | Rearrangement of DNA sequences between exon1 and an adjacent Tip100 (COD) | Purple to stable white | [ |
I. purpurea | CHS-D | One copy of Tip100 insertion in 5'-flanking (COD) | Purple to white, flaked | [ |
I. purpurea | MYB1 | 6-bp and19-bp deletions (COD) | Purple to white flowers with colored rays | [ |
I. purpurea | bHLH | IpMu1 insertion in exon2 and IpMu2 insertion in intron5 (COD) | Bright blue to pale blue | [ |
I. nil | CHS-D | 5.57-kb Tpn3 insertion in intron (COD) | Purple to white flowers with colored tubes | [ |
I. nil | CHI | Tpn2 insertion in intron2 and a speckled-activator (COD) | Purple to white, speckled | [ |
I. nil | DFR-B | Tpn1 insertion in intron2 (COD) | Purple to white, flecked | [ |
I. nil | MYB1 | AG insertion in exon2 (COD) | Blue to white | [ |
I. nil | bHLH | 583-bp tandem duplication derived from exons 5 and 6 (COD) | Bright blue to pale blue | [ |
I. nil | WDR1 | 7-bp (GGAGTAC/TCCGTAC) insertion (COD) | Blue to white | [ |
Torenia fournieri | F3H | A LTR-type retrotransposon (TORE1) insertion in the promoter (CIS) | Violet to white | [ |
T. fournieri | MYB1 | A En/Spm-like transposon (Ttf1) insertion in intron2 (COD) | Purple to white, flecked | [ |
Petunia axillaris | AN2 | Frameshift and nonsense mutations (COD) | Red to white | [ |
Parrya nudicaulis | CHS | Lower expression (CIS) | Purple to white | [ |
Mimulus lewisii | DFR | A frameshift in exon2 (COD) | Pink to white | [ |
Antirrhinum majus ssp. striatum | ROSEAel | Lose of an activator (?) | Dark red to light yellow | [ |
A. majus ssp. Latifolium | ROSEAel | Lose of an activator (?) | Dark red to light yellow | [ |
A. majus ssp. Meonanthemum | ROSEAel | Lose of an activator (?) | Dark red to light yellow | [ |
Antirrhinum (3 species) | ROSEA | Lose of function (COD and CIS) | Red to pale or yellow | [ |
Aquilegia spp. | R2R3-MYB? | ? | Purple to white or yellow | [ |
M. cardinalis SM | PELAN | Gene deletion (?) | Red to yellow | [ |
M. cardinalis CI | PELAN | Lower expression (?) | Red to yellow | [ |
M. guttatus | PELAN | No expression (?) | Red to yellow | [ |
Oriental Lilium spp. | MYB12 | Two amino acid substitutions (COD) | Pink to white | [ |
表3. 花色由蓝/紫/红色到白/黄色变化的基因突变形式
COD代表编码区的突变;CIS代表cis调控区的突变;Trans代表反式作用转录因子的改变;“?”代表原因不详。
物种名 | 基因名 | 突变形式 | 表型变异 | 参考 文献 |
---|---|---|---|---|
Narcissus pseudonarcissus | Narcissus mosaic virus | Viral infection | Color break (figure2a) | [ |
Ipomoea purpurea | CHS-D | One copy of 3.9 kb Tip100 insertion in intron (somatic excision of transposon) | Variegation (white, flaked) (figure 2b) | [ |
I. purpurea | CHS-D | One copy of Tip100 insertion in 5’-flanking (somatic excision of transposon) | Variegation (white, flaked) | [ |
I. nil | CHI | Tpn2 insertion in intron2 and a speckled-activator (somatic excision of transposon) | Variegation (white, speckled) (figure 2c) | [ |
I. nil | DFR-B | Tpn1 insertion in intron2 (somatic excision of transposon) | Variegation (white, flecked) (figure 2d, e) | [ |
Dahlia variabilis | bHLH | A 5.4-kb CACTA transposon (Tdv1) insertion in intron4 (somatic excision of transposon) | Yellow ray florets with orange variegation (figure 2f) | [ |
Torenia fournieri | MYB1 | A En/Spm-like transposon (Ttf1) insertion in intron2 (somatic excision of transposon) | Variegation (white, flecked) | [ |
Petunia hybrida | CHS-A | Lower expression in white margin (siRNA directed silencing in exon2) | White marginal picotee (figure 2g, h) | [ |
P. hybrida | FLS | Higher expression in white center (?) | Colored marginal picotee (figure 2i, j) | [ |
Dahlia variabilis | CHS | Lower expression in white regions (siRNA directed silencing in exon2) | Red-white bicolor (figure 2k) | [ |
Camellia japonica “Tamanoura” | CHS | Lower expression in white regions (?) | White Marginal Picotee | [ |
P. hybrida | CHS-A | Lower expression in white stripe (siRNA directed silencing in exon2) | A star-type red and white bicolor pattern (figure 2l) | [ |
Rudbeckia hirta | F3H, F3’H, FLS, F6H, F7GT | Higher expression in the basal part (?) | UV/bull’s eye pattern (figure 2m, n) | [ |
I. purpurea | CHS-D | Tissue specific expression | Flower limb pigmentation | [ |
CHS-E | Tissue specific expression | Flower tube, ray, and anthers pigmentation | ||
Clarkia gracilis | F3’H1, F3’5’H1, DFR1, DFR2 | Early expression of F3’H1-A throughout the petal and DFR2-A/B in spots; later expression of F3’5’H1-A/B and DFR1-A/B in the petal background (?) | A single red-purple spot against a pink background (figure 2t) | [ |
Paeonia suffruticosa cultivar “Jinrong” | CHS, F3’H, DFR, ANS | Higher expression in the purple spot (?) | Purple spot at the base of white petal | [ |
Pansy (Viola × wittrockiana Gams.) | F3H, F3’5’H, DFR, ANS | Higher expression in the cyanic blotches (?) | Cyanic blotches on the yellow petal | [ |
Antirrhinum ssp. | VENOSA | Tissue specific expression | Petal lobe and tube venation pigmentation (figure 2o) | [ |
Antirrhinum ssp. | ROSEAel | Tissue specific expression | Petal lobe and tube pigmentation | [ |
P. hybrida | DPL | Tissue specific expression | Tube venation pigmentation (figure 2p) | [ |
AN2 | Tissue specific expression | Flower limb pigmentation (figure 2p) | ||
AN4 | Tissue specific expression | Flower tube and anthers pigmentation | ||
PHZ | Tissue specific expression (light induced) | Vegetative tissue pigmentation and bud blushing |
Mimulus lewisii | PELAN | Tissue specific expression | Petal lobe pigmentation | [ |
---|---|---|---|---|
M. lewisii, M. guttatus | NEGAN | Tissue specific expression | Spot formation in the nectar guide | [ |
Phalaenopsis spp. | MYB2 | Tissue specific expression | Full-red pigmentation in tepals | [ |
MYB11 | Tissue specific expression | Red spots in sepals, petals and lip (figure 2v) | ||
MYB12 | Tissue specific expression | Venation pattern in the sepals, petals and the full pigmentation pattern in the central lobe of the lip | ||
Lilium regale | MYB15 | Tissue specific expression (light induced) | Vegetative tissue pigmentation and bud blushing (figure 2s) | [ |
Asiatic Lilium spp. | MYB12 Mon/Ren/Lan | Tissue specific expression | Full-pink pigmentation in tepals | [ |
Asiatic Lilium spp. | MYB6 | Tissue specific expression | Vegetative tissue pigmentation and raised spot in tepals | [ |
Asiatic Lilium spp. cv “Latvia” | MYB12-lat | Tissue specific expression | Splatter spot in tepals (figure 2x) | [ |
Oriental Lilium spp. | MYB12 | Tissue specific expression | Full-pink and raised spot pigmentation in tepals (figure 2w) | [ |
Apple “Honeycrisp” | MYB10 | Lower expression in green stripes (higher methylation in promoter of green stripes) | Red and green stripes on fruit skin | [ |
MYB10 | Higher expression in red regions (light induced) | Blushed fruit skin | ||
Trifolium spp. | RED LEAF | Tissue specific expression | Red leaf, red midrib, and red fleck | [ |
RED V | Tissue specific expression | V-broken yellow and red leaflet | ||
RED LEAF DIFFUSE | Tissue specific expression | Diffuse red leaf | ||
Tulipa gesneriana cv. Murasakizuisho | Vit1 (coding a vacuolar iron transporter) | Tissue specific expression at the bottom of purple perianth | Blue spot at the bottom of the inner purple perianth (figure 2u) | [ |
FER1 (coding an Fe storage protein) | Tissue specific expression at the upper of purple perianth |
表4. 已报道的花色着色模式相关变异
COD代表编码区的突变;CIS代表cis调控区的突变;Trans代表反式作用转录因子的改变;“?”代表原因不详。
高积累而形成类似蜜导的UV模式 [
目前MYB的时空特异性表达机制并不清楚。影响营养组织和芽红着色的R2R3-MYB通常会受光的诱导而高表达,且抑制型的R3-MYB会被激活参与该过程以避免过激反应 [
花色的变异可能会带来传粉者或其访问频率的变异,传粉者与花色的相互关系对花色进化具有重要的意义。长期以来,人们对传粉者在花色亿万年的选择中发挥的作用十分好奇。此外,非传粉者因素(自然环境、病原菌、啃食者、基因多效性等)也会影响花色多态性 [
在陆地植物中发生过多次独立的花色从蓝/紫色到红/粉色或花色从蓝/紫/红色到白/黄色的转换,如曼陀罗属(Iochroma)、番薯属(Ipomoea)、钓钟柳属(Penstemon)、耧斗菜属(Aquilegia) (图3a-d)、闭鞘姜属(Costus) [
通常,花色从蓝/紫色到红/粉色的转换伴随传粉者从蜂类(bees)到蜂鸟(hummingbirds)的转换,从蓝/紫/红色到白/黄色的转换伴随传粉者从蜂类或蜂鸟到蛾类(moths)的转换 [
传粉者对花色表型变异的区别访问是否对花色的进化产生选择性作用,通常要看该区别访问是否造成不同花色类型植物适合度(fitness)的不同 [
多数研究缺乏对不同花色变异的适合度的评估(e.g. [
物种名 | 比较的花色 或着色模式 | 传粉者 | 适合度成分 | 传粉者偏爱性 | 传粉者介导的自然选择 | 非传粉者 因素介导 的自然选择 | 参考文献 |
---|---|---|---|---|---|---|---|
Penstemon digitalis | White, white with purple striping | Small-to large-bodied bees | Fruit set, seed number | - | No | - | [ |
Phlox. drummondii, P. cuspidate | Light/dark blue, light/dark red | Butterflies, moths, and hawkmoths | Fruit set, seed number, survival rate | Light blue | No | - | [ |
Wahlenbergia albomarginata | Blue to white | Solitary bees | Seed number, pollen export | No | No | - | [ |
Iris atropurpurea, | Purple, dark brown | Male bee shelters | Seed set | Dark brown | No | - | [ |
I. haynei | |||||||
Mimulus aurantiacus | Red, yellow | Hummingbirds and hawkmoths | Survival rate, plant size | Hummingbirds for red, hawkmoths for white | - | Red morphs had higher survival rate and plant size than yellow morphs at both coast and inland regions | [ |
Malva moschata | Red, white | Bumblebees and honeybees | Fruit set, seed number | Bumblebees preferred for red, honeybees had no preferences | - | Honeybee abundance may maintain flower color polymorphism | [ |
Bixa orellana | White, amaranth rose, petunia purple, cobalt violet | Honeybees, carpenter bees, ants, and small flies | Fruit set, mature fruit number, seed number, seed mass | Amaranth rose | - | Increased selfing rate of morphs under lower visits may maintain flower color polymorphism | [ |
Clarkia gracilis ssp. sonomensis | Spotted/unspotted pink flowers | Evylaeus pullilabris | Sired seed number, seed number | Weak preference for spotted flowers | - | Small postpollination siring advantages for spotted plants | [ |
Ursinia calenduliflora | spotted, unspotted yellow flowers | Male Megapalpus capensis | Pollen export, number of fertilized ovules | Spotted flowers | - | Herbivores (preference for spotted morph); Low latitude and high altitude were beneficial to spotted morph | [ |
Aquilegia coerulea | White to blue | Bumblebees and hawkmoths | Seed set | Bumblebees for blue, hawkmoths for white | Whiter flowers were associated with the annual presence of hawkmoths. | Higher altitude was correlated with bluer flowers | [ |
Ipomopsis. aggregata, I. tenuituba | Red, pink (hybrids), white | Hummingbirds and hawkmoths | Fruit set, seed set, sired seed number | Hummingbirds for red, hawkmoths for white | Disruptive selection | - | [ |
M. bicolor | All yellow, white and yellow bicolor | Small-bodied bees | Pollen deposition, seed number | No | Avoidance of pollinator competition with M. guttatus in sympatric area, disruptive selection | Latitude explained 52% of the variation in morph frequency across sites | [ |
Antirrhinum majus | Red, yellow, white | Bumblebees | Pollen receipt and export, fruit set | Yellow or white | Maintenance of flower color polymorphism | - | [ |
Claytonia virginica | White to red | Andrena erigeniae | Fruit production, fruit set | - | Directional selection for redness (marginal significant) | Intermediately colored flowers set more fruit than white or red-flowered plants, balancing selection; Herbivores (preferring red morph) showed selection antagonistic to pollinators; Pathogen (preferring infection of white morph) showed selection opposing to herbivores. | [ |
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Lapeirousia oreogena | With or without white arrows-markings | long-proboscid nemestrinid fly Prosoeca sp. nov. | Pollen export, fruit set, seed set | Flowers with white arrows-markings | Directional selection | - | [ |
Centaurea cyanus | Violet-blue (dark, violet and strong UV reflective) | Bumblebees | Fertilization rate, seed number | - | Directional selection | - | [ |
Lysimachia arvensis | Blue, red | Solitary bees and Bombus terrestris | Germination, seedling survival, seedling mass, ovule and pollen production, pollen export, seeds per fruit, seed set | Blue | Directional selection for blue in blue biased population | Dry and hot were beneficial to blue morphs; Delayed selfing may exert balancing selection on red morph in blue biased population | [ |
Gentiana lutea | Yellow to orange | Bumblebees | Seed number | Yellowness in Torrestı´o population | Directional selection in Torrestı´o population; Variation in pollinator communities among populations may maintain color polymorphism | Seed predators avoided yellow flowers in Torrestío population, same directional selection with pollinators; Orangeness increased westward | [ |
Anacamptis morio | Violet-blue (lighter, strong contrast) | Bumblebees | Fruit number, fruit mass | - | Directional selection | - | [ |
Delphinium nelsonii | Blue, white | Hummingbirds and bumblebee queens | Seed set | Blue | Stabilizing selection | - | [ |
I. purpurea | Dark purple (MYB1MYB1), light purple (MYB1myb1), white (myb1) | Bumblebees | Flower number, fruit number, seed mass, seed number, survival rate | When white phenotypes constitute 25% of the population, pollinators were against visiting white flowers; no preference for dark and light flowers | Negative frequency dependent selection | Increased selfing rate of white morph under lower visits and overdominance of heterozygote exerted balancing selection | [ |
Cosmos bipinnatus | Purple, pink, white | Bumblebees and honeybees | Fruit set and seed number per capitulum | Pink | - | Overdominance of heterozygote exerted balancing selection | [ |
Sisyrinchium sp. | Purple (dd), white (DD, Dd) | Bees, hover flies, and thrips | Fruit set, size of mature fruit, seed number | - | - | Overdominance of heterozygote exerted balancing selection | [ |
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P. drummondii | Red, white | Butterflies, moths, and hawkmoths | Flower number, fruit set, seed number, germination, survival rate, fecundity, relative fitness | No | No | Pleiotropy, purifying selection for white individual | [ |
I. purpurea | Purple (CHS-D-), white (chs-d) | Bumblebees | Flower number, survival rate, fecundity, germination | No | No | Pleiotropy, purifying selection for white individual | [ |
Linanthus parryae | Blue, white | Beetles | Seed number | No | No | High spring precipitation was beneficial to white morph, fluctuating selection | [ |
表5. 花色对传粉者和适合度组成分的影响
“比较的花色或着色模式”中粗体部分表示该花色类型适合度较高;“适合度成分”中粗体部分表示有显著差异的适合度成分;“-”表示无实验证据。
图3. 一些属植物花色转换系统树
在进化过程中,植物为适应不同的传粉者会使花部特征特异化。如被蜂鸟传粉的花通常为红色、具有较长的花筒、较窄的花檐、外突的雄蕊和柱头、分泌大量但糖浓度较低的花蜜,被蜂类传粉的花大多为蓝紫色、具较宽的花筒和花檐、内嵌的雄蕊和柱头、分泌少量但高浓度的花蜜,而被蛾类传粉的花则多为白色、花筒较长、有芳香气味且经常在夜间开放,具低浓度高量花蜜 [
非传粉者因素对不同花色类型的适合度也具有一定的影响(表5)。因为不同的花色类型对光照、降水量、温度、海拔、经纬度等环境的适应能力可能不同,所以环境的异质性可导致不同花色类型在不同地区分布的差异 [
基因的多效性也会影响花色。有时,杂合体花色表型会表现出超显性(overdominance) [
花色表型的丰富变异既存在于种间,也存在于种内。花色表型变异的分子机制和自然选择的研究对探究生物多样性的存在机制具有重要意义。目前对种内的数量变异研究相对较少。传粉者或非传粉者因素对花色变异所起的选择作用有可能影响花色的进化,但其作用机制还需要更多研究。已有的研究结果多数还需要生态学的调查加以确认。花色表型变异导致的植物-传粉者关系的变化如何影响物种的分化,进而影响生态系统的动态变化尚需更多关注。特别是随着气候变化的加剧,自然环境对植物性状和传粉者访花行为的影响将越来越受重视。显然,相关研究将会深化我们对未来气候下动植物互作关系的认识。
国家自然科学基金:91331116。
张瑞娟,鲁迎青. 花色表型变异的分子机制及自然选择 Molecular Mechanisms and Natural Selection of Flower Color Variation[J]. 植物学研究, 2016, 05(06): 186-209. http://dx.doi.org/10.12677/BR.2016.56024