Exceptional paternal inheritance of plastids in Arabidopsis suggests that low‐frequency leakage of plastids via pollen may be universal in plants

Plastid DNA is absent in pollen or sperm cells of Arabidopsis thaliana. Accordingly, plastids and mitochondria, in a standard genetic cross, are transmitted to the seed progeny by the maternal parent only. Our objective was to test whether paternal plastids are transmitted by pollen as an exception. The maternal parent in our cross was a nuclear male sterile (ms1-1/ms1-1), spectinomycin-sensitive Ler plant. It was fertilized with pollen of a male fertile RLD-Spc1 plant carrying a plastid-encoded spectinomycin resistance mutation. Seedlings with paternal plastids were selected by spectinomycin resistance encoded in the paternal plastid DNA. Our data, in general, support maternal inheritance of plastids in A. thaliana. However, we report that paternal plastids are transmitted to the seed progeny in Arabidopsis at a low (3.9 x 10(-5)) frequency. This observation extends previous reports in Antirrhinum majus, Epilobium hirsutum, Nicotiana tabacum, Petunia hybrida, and the cereal crop Setaria italica to a cruciferous species suggesting that low-frequency paternal leakage of plastids via pollen may be universal in plants previously thought to exhibit strict maternal plastid inheritance. The genetic tools employed here will facilitate testing the effect of Arabidopsis nuclear mutations on plastid inheritance and allow for the design of mutant screens to identify nuclear genes controlling plastid inheritance.