Cytological abnormalities during pollen development in interspecific hybrids of Nicotiana

Abstract

Nicotiana alata is resistant to Tomato spotted wilt virus (TSWV) and of great value in breeding. However, hybrid sterility constrains the application of interspecific genetic resources. Previously, we obtained interspecific hybrids between a cytoplasmic male sterility (CMS) line of Nicotiana tabacum and N. alata, some of which were pollen sterile. In the present research, we studied the cytological abnormalities during pollen development in sterile hybrids (F1-D) by comparing pollen development with that in fertile hybrids (F1-S) from the same cross. Transmission electron microscopy and DiI staining showed that the membrane structures of microspores and pollen in F1-D sterile hybrids were impaired. Carbol fuchsin staining revealed that cytomixis, chromosome loss and asymmetric callose wall formation occurred with high frequency in the microsporocytes and microspores of the sterile hybrids. The cytoplasm and nucleus were lost in the microspores and pollen of sterile hybrids, leading to mature pollen grains that were vacuous and collapsed in the aperture region. In addition, delayed tapetum degradation was detected in the anther of sterile hybrids, and sporopollenin was deposited in the aperture region. Impaired membrane structures of microspores and pollen in F1-D sterile hybrids affected the integrity of the cells, and might be associated with chromosome, nuclear and cytoplasm loss, vacuous pollen, and sterility in F1-D hybrids. Abnormal tapetum degradation in the anther and irregular sporopollenin deposition in the pollen wall of the F1-D sterile hybrids might also be related to the pollen sterility. This study deepens our understanding of the cytological mechanisms of hybrid sterility, and may facilitate the application of TSWV-resistant resources in cultivated Nicotiana species through hybrid fertility restoration and backcross breeding.

Developmental differences between hermaphrodite and female-like flowers in a non-model horticultural plant <i>Dianthus hybrida</i>

“…Overall, around stages 11-3 and 11-4, many cells of both hermaphrodite and female-like displayed no detectable nuclei signal: we were not sure whether the microspore had successfully undergone mitosis as the nuclei signals became less distinct over the developmental timeline. Nuclei-less pollen observed in late-stages flowers of both hermaphrodite and female-like plants might have been due to genetic incompatibility arising from interspecific hybridisation (Liao et al 2020), preventing complete maturation of the microspore. To be noted that this lack of nuclei signal was not due to non-penetration of DAPI through the cell membranes since mature S. latifolia pollen nuclei DAPI signal could be seen by applying the same method (Fig.…”

“…Whether male sterility is occurring in D. hybrida cv. Telstar Scarlet female-like population has not been reported and may arise from interspecific hybridization (Liao et al 2020), parental lines inheritance, or simply spontaneous mutations (Kinoshita et al 1982). Regardless, the phenomena where female and hermaphrodite populations are present in one species is called gynodioecy, and it occurs relatively frequently among Caryophyllaceae, to which Dianthus [e.g., D. shinanensis, D. superbus (Kuhara and Sugawara 2002), D. pavonius (Bruns et al 2019)] and the dioecious Silene latifolia belong.…”

Hybridization and introgression events in cooccurring populations of closely related grasses (Poaceae: Stipa) in high mountain steppes of Central Asia

“…However, hybridization can also cause a decrease in fitness and genetic swamping [6][7][8], which breaks species identity and could cause extinction [9]. Due to reduced pollen viability, one common consequence of hybridization is a decrease in fertility in the F1 generation [10][11][12][13][14]. Hybrids may exhibit lower fitness due to various factors such as natural selection against hybrids, hybridization load, and hybrid incompatibilities.…”