Tang and Wang et al. explore the mechanism underlying pollen tube tip swelling in the self-incompatibility response.
By Chao Tang1,2, Peng Wang1,2, Shaoling Zhang1,2 and Juyou Wu1,2,3
1 Sanya Institute of Nanjing Agricultural University, State Key Laboratory of Crop Genetics & Germplasm Enhancement and Utilization, Nanjing Agricultural University, Nanjing 210095, China
2 Jiangsu Engineering Research Center for Pear, Nanjing 210014, China
3 Jiangsu Key Laboratory for Horticultural Crop Genetic Improvement, Nanjing 210014, China
Background: Self-incompatibility is a widespread genetic mechanism in flowering plants that prevents self-fertilization and promotes outbreeding. S-RNase-based SI is characterized by the arrest of pollen tube growth through the pistil, resulting in disrupted and swollen pollen tube tips that do not reach the ovule and therefore fail to complete fertilization. However, the underlying molecular mechanism responsible for pollen tube tip swelling is still largely unknown.
Question: Which factors play roles in pollen tube tip swelling during the self-incompatibility response?
Findings: Here we report that the swelling at the tips of incompatible pollen tubes in pear is mediated by self-incompatibility–induced acetylation of the soluble inorganic pyrophosphatase PbrPPA5. Acetylation at Lys-42 of PbrPPA5 by the acetyltransferase PbrGNAT1 caused PbrPPA5 to accumulate in the nucleus. Acetylated PbrPPA5 bound to the transcription factor PbrbZIP77 to form a transcriptional repression complex that inhibited the expression of the pectin methylesterase gene PbrPME44. Downregulating PbrPME44 resulted in increased levels of methyl esterified pectins in growing pollen tubes, leading to swelling at their tips.
Next steps: In future studies, we aim to further investigate how the acetyltransferase PbrGNAT1 responds to self-incompatibility signaling and how the soluble inorganic pyrophosphatase PbrPPA5 accumulates in the nucleus.
Chao Tang, Peng Wang, Xiaoxuan Zhu, Kaijie Qi, Zhihua Xie, Hao Zhang, Xiaoqiang Li, Hongru Gao, Tingting Gu, Chao Gu, Shan Li, Barend H. J. de Graaf, Shaoling Zhang, Juyou Wu. (2023). Acetylation of inorganic pyrophosphatase by S-RNase signaling induces pollen tube tip swelling by repressing pectin methylesterase. https://doi.org/10.1093/plcell/koad162