Membrane receptor-mediated mechano-transduction maintains cell integrity during pollen tube growth within the pistil

OsMTD2-mediated reactive oxygen species (ROS) balance is essential for intact pollen-tube elongation in rice

The highly specialized haploid male gametophyte-pollen consist of two sperm cells and a large vegetative cell. Successful fertilization requires proper growth timing and rupture of the pollen tube until it delivers sperm cells, which occur immediately after a pollen grain hydrates. Although a tight regulation on polar cell-wall expansion of the pollen tube is fundamentally important, the underlying molecular mechanism remains largely unknown, especially in crop plants. Here, we characterized the function of male-gene transfer defective 2 (OsMTD2) gene in rice (Oryza sativa), which belongs to the plant-specific receptor-like kinase, the CrRLK1L family. We demonstrated that OsMTD2 is an essential male factor participating in pollen-tube elongation based on genetic evidence and physiological observations. Because of unavailability of homozygous mutant via conventional methods, we used CRISPR-Cas9 system to obtain homozygous knockout mutant of OsMTD2. We were able to identify phenotypic changes including male sterility due to early pollen-tube rupture in the mutant. We observed that the production of reactive oxygen species (ROS) was dramatically reduced in mutants of OsMTD2 pollen grain and tubes with defective pectin distribution. Transcriptome analysis of osmtd2-2 versus wild-type anthers revealed that genes involved in defense responses, metabolic alteration, transcriptional and protein modification were highly upregulated in the osmtd2-2 mutant. Through yeast-two-hybrid screening, we found that OsMTD2 kinase interacts with E3 ligase SPL11. Taken together, we propose that OsMTD2 has crucial functions in promoting pollen-tube elongation through cell-wall modification, possibly by modulating ROS homeostasis during pollen-tube growth.

Feeling the pressure: A mechanical tale of the pollen tube journey through the pistil

The pollen tube grows inside the pistil, carrying male gametes to the ovule. During this journey, it invades diverse tissues, sensing and adapting to abrupt transitions in mechanical environment. In this issue of Developmental Cell, Zhou et al. identify a receptor-like kinase/Rho-GTPase module that regulates adaptation to such a transition.