Thapa Sita, Patel Jayna A, Reuter-Carlson Ursula, Schroeder Nathan E
Department of Crop Sciences, University of Illinois at Urbana-Champaign, 1102 S. Goodwin Ave, Urbana, 61801, IL, USA.
BMC Dev Biol. 2017 Jan 11;17(1):2. doi: 10.1186/s12861-016-0144-7.
Many parasites regulate their development to synchronize their life cycle with a compatible host. The parasitic nematode Heterodera glycines displays incomplete host-mediated hatching behavior wherein some H. glycines individuals hatch only in the presence of a host-derived cue while others hatch in water alone. Furthermore, H. glycines shows variable hatching behavior based on oviposition location. The mechanisms regulating this hatching variability are unknown. In this study, we established a detailed timeline of the H. glycines pre-hatch development from early embryogenesis to the pre-hatched J2. These descriptive data were then used to test hypotheses regarding the effect of host stimulus and oviposition location on pre-hatch development.
We found that H. glycines develops from a single-cell egg to a fully formed J2 in approximately 172 hours. The stylet-based mouthpart, which is used to pierce the eggshell during hatching, is not completely formed until late in pre-hatch J2 development and is preceded by the formation of stylet protractor muscles. We also found that the primary motor nervous system of H. glycines did not complete development until late in pre-hatch J2 development. These data suggest possible structural requirements for H. glycines hatching. As expected, exposure of H. glycines eggs to host-derived cues increased the percentage of nematodes that hatched. However, exposure to hatching cues did not affect pre-hatch development. Similarly, we found no obvious differences in the pre-hatch developmental timeline between eggs laid in an egg sac or retained within the mother.
The pattern of early embryonic development in H. glycines was very similar to that recently described in the related parasitic nematode Meloidogyne incognita. However, the speed of H. glycines pre-hatch development was approximately three times faster than reported for M. incognita. Our results suggest that hatching stimulants do not affect embryogenesis itself but only influence the hatching decision once J2 development is complete. Similarly, the oviposition location does not alter the rate of embryogenesis. These results provide insight into the primary survival mechanism for this important parasite.
许多寄生虫会调节自身发育，使其生命周期与合适的宿主同步。寄生线虫大豆胞囊线虫表现出不完全的宿主介导孵化行为，即一些大豆胞囊线虫个体仅在存在宿主衍生信号时才孵化，而其他个体则单独在水中孵化。此外，大豆胞囊线虫根据产卵位置表现出可变的孵化行为。调节这种孵化变异性的机制尚不清楚。在本研究中，我们建立了从早期胚胎发生到孵化前J2期的大豆胞囊线虫孵化前发育的详细时间线。然后利用这些描述性数据来检验关于宿主刺激和产卵位置对孵化前发育影响的假设。
我们发现大豆胞囊线虫从单细胞卵发育到完全形成的J2期大约需要172小时。用于在孵化时刺穿卵壳的基于口针的口器直到孵化前J2期发育后期才完全形成，并且在口针牵引肌形成之前形成。我们还发现大豆胞囊线虫的初级运动神经系统直到孵化前J2期发育后期才完成发育。这些数据表明了大豆胞囊线虫孵化可能的结构要求。正如预期的那样，将大豆胞囊线虫卵暴露于宿主衍生信号会增加孵化的线虫百分比。然而，暴露于孵化信号并不影响孵化前发育。同样，我们发现在卵囊中产卵或保留在母体内的卵在孵化前发育时间线上没有明显差异。
大豆胞囊线虫早期胚胎发育模式与最近描述的相关寄生线虫南方根结线虫非常相似。然而，大豆胞囊线虫孵化前发育的速度比南方根结线虫报道的速度快约三倍。我们的结果表明，孵化刺激物不会影响胚胎发生本身，而是仅在J2期发育完成后影响孵化决定。同样，产卵位置不会改变胚胎发生的速率。这些结果为这种重要寄生虫的主要生存机制提供了见解。
