Donald Danforth Plant Science Center, St. Louis, Missouri 63132.
Department of Biology, Washington University, St. Louis, Missouri 63130.
Plant Cell. 2020 Nov;32(11):3500-3518. doi: 10.1105/tpc.20.00424. Epub 2020 Sep 1.
Sorghum () and its relatives in the grass tribe Andropogoneae bear their flowers in pairs of spikelets in which one spikelet (seed-bearing or sessile spikelet [SS]) of the pair produces a seed and the other is sterile or male (staminate). This division of function does not occur in other major cereals such as wheat () or rice (). Additionally, one bract of the SS spikelet often produces a long extension, the awn, that is in the same position as, but independently derived from, that of wheat and rice. The function of the sterile spikelet is unknown and that of the awn has not been tested in Andropogoneae. We used radioactive and stable isotopes of carbon, RNA sequencing of metabolically important enzymes, and immunolocalization of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) to show that the sterile spikelet assimilates carbon, which is translocated to the largely heterotrophic SS. The awn shows no evidence of photosynthesis. These results apply to distantly related species of Andropogoneae. Removal of sterile spikelets in sorghum significantly decreases seed weight (yield) by ∼9%. Thus, the sterile spikelet, but not the awn, affects yield in the cultivated species and fitness in the wild species.
高粱及其在禾本科中的亲缘植物在每一对小穗中产生花朵，其中一对小穗中的一个小穗（结实或无梗小穗 [SS]）产生种子，另一个小穗则为不育或雄性（雄花）。这种功能的分工在其他主要谷物如小麦或水稻中并不存在。此外，SS 小穗的一个苞片通常会产生一个长的延伸物，即芒，其位置与小麦和水稻的芒相同，但芒是独立衍生的。不育小穗的功能未知，禾本科中的芒的功能也尚未得到验证。我们使用碳的放射性和稳定同位素、对代谢重要酶的 RNA 测序以及 1,5-二磷酸核酮糖羧化酶/加氧酶（Rubisco）的免疫定位，表明不育小穗同化了碳，这些碳被转运到大部分异养的 SS 中。芒没有光合作用的证据。这些结果适用于禾本科中的亲缘关系较远的物种。高粱中不育小穗的去除会使种子重量（产量）显著减少约 9%。因此，不育小穗而非芒会影响栽培物种的产量和野生物种的适应性。
