Plasticity in the self-incompatibility system of cultivated Nicotiana alata
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Nicotiana alata has long been a model species for studying gametophytic self-incompatibility (SI) in Solanaceae. Genetically based SI systems are widespread in flowering plants and function to reduce homozygosity and avoid inbreeding depression. However, out-crossing is always unfulfillable for populations with few S-alleles, such as in cultivated clonal populations or populations founded by few individuals. Under such conditions, there is a pressing demand to self-reproduce and pass on genetic information. We carried out a series of pollination and pollen tube observation experiments to explore how homozygous self-incompatible N. alata (S-allele identified and S-RNase active) sets fruits and to explore pseudo-self-fertility in these individuals. We observed several kinds of pollen tube abnormalities, including swelling, furcation, curve and inflexion, tip bursting and irregular callose plug deposition for flowers pollinated at different developmental stages. In addition, SI strength in this line of N. alata plants changed with floral age and flowering stages. That is, flowers became more self-compatible with floral aging, and SI strength in flowers at the end of flowering stages (stage III) was lower and more fruits were set at the top of the pseudo-raceme. Finally, SI strength also varied between individual flowers at the same plant and development stages. However, SI strength varied insignificantly among cultivated N. alata plants homozygous for the same S-allele. These findings indicate that SI in N. alata is plastic, with fruits set by aging flowers, especially flowers at stage III.
KeywordsNicotianaalata Self-incompatibility (SI) Pseudo-self-fertility (PSF) Pollination Pollen tubes
This study was partly supported by grant 31560419 from the National Natural Science Fund in China.
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