Abstract
In the life cycle of a flowering plant, the male gametophyte (pollen grain) produced in the anther reaches the stigmatic surface and initiates the pollen–pistil interaction, an important step in plant reproduction, which ultimately leads to the delivery of two sperm cells to the female gametophyte (embryo sac) inside the ovule. The pollen tube undergoes a strictly apical expansion characterized by a high growth rate, whose targeting should be tightly regulated. A continuous exchange of signals therefore takes place between the haploid pollen and diploid tissue of the pistil until fertilization. In compatible interactions, theses processes result in double fertilization to form a zygote (2n) and the triploid endosperm. Among the large number of signaling mechanisms involved, the redox network appears to be particularly important. Respiratory burst oxidase homologs (Rbohs) are superoxide-producing enzymes involved in a broad range of processes in plant physiology. In this study, we review the latest findings on understanding Rboh activity in sexual plant reproduction, with a particular focus on the male gametophyte from the anther development stages to the crowning point of fertilization. Rboh isoforms have been identified in both the male and female gametophyte and have proven to be tightly regulated. Their role at crucial points such as proper growth of pollen tube, self-incompatibility response and eventual fertilization is discussed.
Highlights
Reviewed by: Wei-Hua Tang, Chinese Academy of Sciences, China Miguel Angel Torres, Universidad Politécnica de Madrid, Spain
We review the latest findings on understanding Respiratory burst oxidase homologs (Rbohs) activity in sexual plant reproduction, with a particular focus on the male gametophyte from the anther development stages to the crowning point of fertilization
An apoplastic peroxidase-catalyzed oxidative burst following biotic stress has been described in different species such as Arabidopsis thaliana or Phaseolus vulgaris (Bolwell et al, 2002; O’Brien et al, 2012), NADPH oxidase and other sources including mitochondria contribute to reactive oxygen specie (ROS) generation (O’Brien et al, 2012)
Summary
The superoxide radical (O2−), a short-lived reactive oxygen specie (ROS) characterized by moderate reactivity, is able to trigger a cascade of reactions (enzymatic, metal-catalyzed, and even direct reactions) in order to produce others ROS species. Apart from the production of free radicals that occurs as a result of the side reactions of metabolism and electron leakage, the plant oxidative burst was first described as the physiologically-controlled and rapid ROS generation during the early responses to pathogen infections, to what occurs in animal phagocytic cells. This process has been described as involving the activity of NADPH oxidase enzymes, called Rbohs, in plants (Lamb and Dixon, 1997). Rboh-derived O2− has been shown to mediate cell-to-cell communication over long distances in plants (Miller et al, 2009)
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