遗传控制的自交不亲和(SI)机制限制了自交,因此促进了开花植物的进化多样性。在同态配子体SI(GSI)和同态孢子体SI(SSI)中,遗传控制通常是通过单个多等位基因位点S进行的。GSI和SSI都阻止自花粉管到达卵巢,因此是合子前的作用。相比之下,在具有后期作用的自我不兼容(LSI)的类群中,排斥反应通常是合子后,因为自花粉管长到子房,受精可能发生在花脱落之前。或者,缺乏自我坐果可能是由于早期作用的近亲繁殖抑郁症(EID)。我们研究的目的是研究Handroanthusheptaphylus中缺乏自交水果的潜在机制,以评估LSI与EID的可能性。
我们使用了四个全同胞diallels,使用早熟开花变体研究了H.heptaphylus中LSI的遗传控制。我们还使用荧光显微镜研究了花粉管在授粉或启动果实后脱落的雌蕊中胚珠渗透的发生率。
所有拨号显示相互交叉不相容的全同胞(RCI),相互交叉兼容的全同胞(RCC)和非相互兼容的全同胞(NRC),比例几乎相等。在自交和杂交不相容授粉后,脱落的雌蕊中胚珠穿透的发生率没有显着差异,但是那些成功的异花授粉大约2倍。
一个遗传模型假设一个具有四个S等位基因的单个S基因座,其中之一,在母亲的父母,对其他三个占主导地位,将产生33%的RCI、RCC和NRC全同胞情况,与我们的Dialell结果一致。我们赞成这种简单的遗传控制而不是EID解释,因为我们没有授粉,成功或不成功,导致部分胚胎发育,正如在全基因组EID效应下所预期的那样。
Genetically controlled self-incompatibility (SI) mechanisms constrain selfing and thus have contributed to the evolutionary diversity of flowering plants. In homomorphic gametophytic SI (GSI) and homomorphic sporophytic SI (SSI), genetic control is usually by the single multi-allelic locus S. Both GSI and SSI prevent self pollen tubes reaching the ovary and so are pre-zygotic in action. In contrast, in taxa with late-acting self-incompatibility (LSI), rejection is often post-zygotic, since self pollen tubes grow to the ovary, where fertilization may occur prior to floral abscission. Alternatively, lack of self fruit set could be due to early-acting inbreeding depression (EID). The aim of our
study was to investigate mechanisms underlying the lack of selfed fruit set in Handroanthus heptaphyllus in order to assess the likelihood of LSI versus EID.
We employed four full-sib diallels to
study the genetic control of LSI in H. heptaphyllus using a precociously flowering variant. We also used fluorescence microscopy to
study the incidence of ovule penetration by pollen tubes in pistils that abscised following pollination or initiated fruits.
All diallels showed reciprocally cross-incompatible full sibs (RCIs), reciprocally cross-compatible full sibs (RCCs) and non-reciprocally compatible full sibs (NRCs) in almost equal proportions. There was no significant difference between the incidences of ovule penetrations in abscised pistils following self- and cross-incompatible pollinations, but those in successful cross-pollinations were around 2-fold greater.
A genetic model postulating a single S locus with four S alleles, one of which, in the maternal parent, is dominant to the other three, will produce RCI, RCC and NRC full sib situations each at 33 %, consistent with our diallel results. We favour this simple genetic control over an EID explanation since none of our pollinations, successful or unsuccessful, resulted in partial embryo development, as would be expected under a whole-genome EID effect.