Transformation of Seed Non-Transmissible Hop Viroids in <i>Nicotiana</i> <i>benthamiana</i> Causes Distortions in Male Gametophyte Development
Viroids are small, non-coding, parasitic RNAs that promote developmental distortions in sensitive plants. We analyzed pollen of <i>Nicotiana benthamiana</i> after infection and/or ectopic transformation with cDNAs of citrus bark cracking viroid (CBCVd), apple fruit crinkle viroid (AFCVd)...
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| Autores principales: | , , , , , |
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| Formato: | article |
| Lenguaje: | EN |
| Publicado: |
MDPI AG
2021
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| Materias: | |
| Acceso en línea: | https://doaj.org/article/ff7e5d4361cf4b8eaba1f0bde12980ce |
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| Sumario: | Viroids are small, non-coding, parasitic RNAs that promote developmental distortions in sensitive plants. We analyzed pollen of <i>Nicotiana benthamiana</i> after infection and/or ectopic transformation with cDNAs of citrus bark cracking viroid (CBCVd), apple fruit crinkle viroid (AFCVd) and potato spindle tuber viroid (PSTVd) variant AS1. These viroids were seed non-transmissible in <i>N. benthamiana</i>. All viroids propagated to high levels in immature anthers similar to leaves, while their levels were drastically reduced by approximately 3.6 × 10<sup>3</sup>, 800 and 59 times in mature pollen of CBCVd, AFCVd and PSTVd infected <i>N. benthamiana,</i> respectively, in comparison to leaves. These results suggest similar elimination processes during male gametophyte development as in the <i>Nicotiana tabacum</i> we presented in our previous study. Mature pollen of <i>N. benthamiana</i> showed no apparent defects in infected plants although all three viroids induced strong pathological symptoms on leaves. While <i>Nicotiana</i> species have naturally bicellular mature pollen, we noted a rare occurrence of mature pollen with three nuclei in CBCVd-infected <i>N. benthamiana</i>. Changes in the expression of ribosomal marker proteins in AFCVd-infected pollen were detected, suggesting some changes in pollen metabolism. <i>N. benthamiana</i> transformed with 35S-driven viroid cDNAs showed strong symptoms including defects in pollen development. A large number of aborted pollen (34% and 62%) and a slight increase of young pollen grains (8% and 15%) were found in mature pollen of AFCVd and CBCVd transformants, respectively, in comparison to control plants (3.9% aborted pollen and 0.3% young pollen). Moreover, pollen grains with malformed nuclei or trinuclear pollen were found in CBCVd-transformed plants. Our results suggest that “forcing” overexpression of seed non-transmissible viroid led to strong pollen pathogenesis. Viroid adaptation to pollen metabolism can be assumed as an important factor for viroid transmissibility through pollen and seeds. |
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