Functional redundancy of transcription factors SlNOR and SlNOR-like1 is required for pollen development in tomato

Abstract

In tomato, SlNOR and SlNOR-like1, members of the NAC family of transcription factors (TFs), are known to play critical roles in regulating fruit ripening and are highly expressed in floral organs. However, their role in flower development remains unclear. In this study, we generated and functionally characterized a double knockout mutant, nor/nor-like1. Our findings reveal that the pollen abortion of the nor/nor-like1 impedes ovarian enlargement, resulting in fruit formation failure. Histological analyses demonstrate that the pollen wall collapse occurs during the mature pollen stage and leads to the abnormal pollen wall component deposition at the microspore stage, resulting in the male sterility in the double knockout mutant lines. Kyoto Encyclopedia of Genes and Genomes enrichment pathway analyses further suggest that the loss of SlNOR and SlNOR-like1 function affects several metabolic pathways related to pollen development, including ‘ABC transporters’, ‘lipid metabolism’, ‘phenylpropanoid biosynthesis’, ‘hormone signal transduction’, ‘starch and sucrose metabolism’, and ‘cutin, suberine, and wax biosynthesis’. Furthermore, our results demonstrate that SlNOR and SlNOR-like1 could directly bind to the promoters of key genes associated with pollen wall formation and activate their expression, including ATP-binding cassette transporters of the G family (SlABCG8/9/23), ECERIFERUM (SlCER1), and glycine-rich protein (SlGRP92). These findings suggest that SlNOR and SlNOR-like1 may play a redundant role in the biosynthesis and transport of sporopollenin precursors, cuticular wax biosynthesis, and exine formation. In summary, our study highlights a previously uncharacterized role of SlNOR and SlNOR-like1 in tomato pollen wall formation and male fertility.

Acknowledgments

This work was funded by the National Natural Science Foundation of China (32072277).

Author Contributions

Da-Qi Fu conceived the project and supervised the work. Hong-Li Li and Ying Gao performed most of the experiments and analyzed the data and drafted the manuscript. Lan-Ting Xiang performed some of the experiments. Xiao-Dan Zhao, Ben-Zhong Zhu, Hong-Liang Zhu, and Gui-Qin Qu provided technical supports. Cai-Zhong Jiang and Yun-Bo Luo contributed to the editing and revising of the manuscript.

Data Availability

All relevant data can be found within the article and its supporting materials.

Conflict of interest statement

No conflict of interest declared.

Supplementary data

Supplementary data is available at Horticulture Research online.

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