Morphological and Cytological Characterization of Petaloid-type Cytoplasmic Male Sterility in Camellia oleifera

Abstract

<jats:p><jats:italic>Camellia oleifera</jats:italic> is an important woody tree species in China that produces edible oil. Although sterile male <jats:italic>C. oleifera</jats:italic> plants play an important role in hybrid breeding, the possible cytological characteristics of pollen abortion remain unknown. To characterize the pollen abortion process, a genic petaloid-type sterile male <jats:italic>C. oleifera</jats:italic> ‘X1’ plant was investigated using a cytological method. The results showed that in male-fertile plants, the anthers were full and butterfly shaped, the pollen viability was as high as 97.5%, and the development of the tapetum and anther vascular bundles was normal. However, in male-sterile <jats:italic>C. oleifera</jats:italic> ‘X1’, petaloidy in the anther was observed, and the pollen vitality was as low as 4.5%. Pollen abortion in sterile <jats:italic>C. oleifera</jats:italic> ‘X1’ anthers occurred from the microspore stage to the mature pollen period. Further cytological analyses revealed an abnormally enlarged tapetum and retarded tapetum degeneration, suggesting that insufficient nutrients were provided for microspore development. Moreover, the anther vascular bundles displayed hyperplasia, and the pollen sac area became increasingly smaller, causing most anthers to be sterile and to have few pollen grains. Taken together, the results indicate that petaloid-type male sterility in <jats:italic>C. oleifera</jats:italic> may be attributed to abnormal development of the tapetum and anther vascular bundles. The findings clarify the pollen abortion period and the cytological characteristics of petaloid-type cytoplasmic male sterility in <jats:italic>C. oleifera</jats:italic>, and lay a solid foundation for the male sterile line in <jats:italic>C. oleifera</jats:italic> hybrid breeding.</jats:p>

Anatomical Characteristics of Petalized Anther Abortion in Male Sterile Camellia oleifera Plants

“…Pollen abortion can occur in every stage of the anther development process, and different species show different manifestations (Laser and Lersten, 1972). It has been found that anther browning and petaloid anthers exist in male sterile plants of the Camellia genus (Jiang et al, 2020;Xiong et al, 2019). These two abortion means are also the main routes of abnormal anther development in other plants (Kozik et al, 2012).…”

“…In the subsequent development stages, anticlinal division was maintained only on the ends of the cross section in the petaloid area of anthers. The development of petaloid anthers was described as the development of the connective tissue of the anthers (Xiong et al, 2019), resulting from the high-frequency division of the middle and peripheral anther cells (He et al, 2010). However, in this study, the cells in the middle of the anthers were lightly stained, while the cells at both ends were darkly stained, indicating that the nuclei of the cells at both ends were active and more cells were observed to be in the division phase in these areas.…”

“…Nutrient transfer and transformation exist during the development of the anther (Wei et al, 2013); however, whether abnormalities in nutrient transfer and transformation occur in the anthers of sterile C. oleifera plants remains to be investigated. The timely degradation of the tapetum layer can release the cell inclusions of the tapetum layer into the anther cells (Parish and Li, 2010); however, its delayed degradation caused C. oleifera and Camellia crassocolumna to be unable to form viable pollen (Jiang et al, 2020;Xiong et al, 2019). This premature degradation also led to the occurrence of male sterility in rice (Shi et al, 2009).…”

“…The flower of C. oleifera is bisexual, and the male sterile plant serves as the female parent. Selecting a suitable male parent and then planting the male and female parents according to a proper proportion can make the male sterile plant accept target pollen in a natural pollination manner at the lowest cost; this strategy will undoubtedly accelerate the process of C. oleifera breeding (Xiong et al, 2019). Therefore, exploring the mechanism of male sterility in plants has always been a hot spot in the field of botany.…”

“…Male sterile C. oleifera plants found early cannot be directly applied to production due to the small sizes of their wild populations, low yields, and long breeding cycles. However, male sterile C. oleifera plants have been of great importance in boosting the production of C. oleifera (Chen et al, 2011;Xiong et al, 2019).…”