Abstract
Understanding the behavior of pollen during pollination is important for food security in the future. The elucidation of pollen development and growth regulation largely relies on the study of the dicotyledonous model plant Arabidopsis thaliana. However, rice (Oryza sativa) pollen exhibits different characteristics to that of Arabidopsis. The latter undergoes programmed dehydration and withstands adverse environmental conditions, whereas rice pollen is sensitive to desiccation. Moreover, the short longevity of rice pollen significantly hampers hybrid seed production. Although the “omics” data for mature rice pollen have been accumulated, few genes that control pollination and pollen hydration have been identified. Therefore, to facilitate future studies, it is necessary to summarize the developmental processes involved in pollen production in rice and to consolidate the underlying mechanisms discovered in previous studies. In this review, we describe the pollen developmental processes and introduce gametophytic mutants, which form defective pollen in Arabidopsis and rice. In addition, we discuss the perspectives on the research on pollen longevity, adhesion and hydration.
Highlights
During the final stage of maturation, pollen grains are generally dehydrated to reach a metabolically inactive state [1]
Rice produces recalcitrant pollen grains, which become unviable within five minutes of exposure to air because of their sensitivity to desiccation [5]
In Arabidopsis and rice, the pollen wall is known to be a multilayered structure: (1) the intine is the innermost pollen wall and mainly comprises pectin, cellulose, hemicellulose and proteins; (2) the pollen coat fills the empty cavities of the exine and contains lipids, proteins, pigments and aromatic compounds; and (3) the exine is the outer pollen wall and contains multilayered sporopollenin [6,7]
Summary
During the final stage of maturation, pollen grains are generally dehydrated to reach a metabolically inactive state [1]. This improves the resistance of “orthodox” pollen to environmental changes [1,2]. To maintain or improve the yield of rice, pollen must rapidly land on the stigma and hydrate before losing water (Figure 1A,B) [5]. Rapid pollen swelling isswelling the driving force behind rupture the anther arrows indicate indicate the pressure caused by swollen mature pollen grains;. The pollen coat is mobilized on the stigma to form a after landing on the stigma. The pollen coat is mobilized on the stigma to form a “pollen foot”.
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