Male sterility in plants refers to the inability to produce functional pollen, which plays a significant role in hybrid seed production by facilitating cross-pollination. Among various male sterility systems, the two-line system based on photoperiod- and thermo-sensitive genic male sterility (P/TGMS) has proven advantageous. P/TGMS lines exhibit male sterility under high temperatures or long-day conditions, making them suitable for hybrid seed production. Conversely, they regain fertility under low temperatures or short-day conditions, allowing self-reproduction.

Mechanisms Underlying P/TGMS Fertility

The fertility of a P/TGMS line depends on microspore development and its ability to withstand environmental fluctuations. Several key mechanisms have been identified:

  • Reactive Oxygen Species (ROS) Homeostasis: Proper regulation of ROS levels influences fertility restoration in P/TGMS lines.
  • Developmental Regulation: Slow development in reproductive tissues under unfavorable conditions can contribute to sterility.

Multiple P/TGMS genes have been identified in rice, maize, sorghum, wheat, and tomato, each controlling pollen formation through distinct molecular pathways (Fan & Zhang, 2018). These genes offer unique mechanisms for fertility restoration in crop breeding programs.

Advances in P/TGMS Line Development

Traditionally, most P/TGMS lines were identified through random discoveries. However, recent advancements have led to more targeted genetic screening strategies, including:

  • Ethyl Methane Sulfonate (EMS) Mutagenesis: A chemical-induced mutagenesis approach to generate novel P/TGMS mutants.
  • Gene Editing: CRISPR and other gene-editing techniques enable precise modifications to P/TGMS-related genes.
  • Mutant Libraries: Large-scale screening of mutant populations to identify novel P/TGMS candidates.

Key Molecular Players in P/TGMS Regulation

Recent research has uncovered critical genetic components involved in P/TGMS regulation:

  • MYB Transcription Factors: Rice has evolved two MYB proteins, CSA2 and CSA, which regulate sugar transport in anthers under long-day and short-day conditions, respectively (Wang et al., 2021). This highlights the photoperiodic regulation of male fertility.
  • Novel P/TGMS Lines: The rice line ostms15, obtained via genetic screening, demonstrates stable sterility under long photoperiods and high temperatures. However, its fertility is restored under low temperatures, emphasizing temperature’s predominant role in TGMS traits (Han et al., 2023).

Conclusion

The understanding of P/TGMS mechanisms has significantly evolved, offering new avenues for hybrid seed production. Advances in genetic screening and molecular research continue to refine breeding strategies, ensuring more stable and efficient hybrid crop production. Future research will likely focus on fine-tuning environmental responsiveness to enhance the adaptability of P/TGMS lines in diverse agricultural conditions.

References

  1. Fan, Y., & Zhang, Q. (2018). Genetic and molecular characterization of photoperiod and thermo-sensitive male sterility in rice. Plant Reprod., 31, 3–14.
  2. Han, Y., Jiang, S. Z., Zhong, X., Chen, X., Ma, C. K., Yang, Y. M., Mao, Y. C., Zhou, S. D., Zhang, Y. F., & Huang, X. H. (2023). Low temperature compensates for defective tapetum initiation to restore the fertility of the novel TGMS line ostms15. Plant Biotechnol. J., 21, 1659–1670.
  3. Wang, D., Li, J., Sun, L., Hu, Y., Yu, J., Wang, C., Zhang, F., Hou, H., Liang, W., & Zhang, D. (2021). Two rice MYB transcription factors maintain male fertility in response to photoperiod by modulating sugar partitioning. New Phytol., 231, 1612–1629.