BcMF27 , a Pectin Methylesterase Gene, Regulates Pollen Development And Pollen Tube Growth in Brassica Campestris

Functional pollen grains are an essential ingredient of successful reproduction in flowering plants and are protected by outer walls. Pectin methylesterases (PMEs) modify pectin, a structural component of pollen intine. However, there are few studies on PMEs. Artificial microRNA (amiRNA) and overexpression technology was performed to investigate the function of pollen-specific PME gene, BcMF27, in pollen development. Knockdown of BcMF27 led to pollen wall collapse, 20% of which unknown material adhered to. Wall-collapsed pollen had abnormally thick intine outside of the germinal furrows. A portion of the cytoplasm was degraded in the remaining pollen with unknown material on the wall, in addition to a thick intine. Overexpression of BcMF27 resulted in 66.67% pollen wall disruption, causing an abnormally thick intine. In addition, functional interruption of BcMF27 gave rise to pollen tubes twisted in vitro. Taken together, BcMF27 contributes to the intine morphogenesis during pollen development and stabilizes pollen tube elongation. This research can promote knowledge of PMEs function and the molecular mechanism in pollen wall construction.

BcMF27, A Pectin Methylesterase Gene, Regulates Pollen Development and Pollen Tube Growth in Brassica Campestris

Functional pollen grains are an essential ingredient of successful reproduction in flowering plants and are protected by outer walls. Pectin methylesterases (PMEs) modify pectin, a structural component of pollen intine. However, there are few studies on PMEs. Artificial microRNA (amiRNA) and overexpression technology was performed to investigate the function of pollen-specific PME gene, BcMF27, in pollen development. Knockdown of BcMF27 led to pollen wall collapse, 20% of which unknown material adhered to. Wall-collapsed pollen had abnormally thick intine outside of the germinal furrows. A portion of the cytoplasm was degraded in the remaining pollen with unknown material on the wall, in addition to a thick intine. Overexpression of BcMF27 resulted in 66.67% pollen wall disruption, causing an abnormally thick intine. In addition, functional interruption of BcMF27 gave rise to pollen tubes twisted in vitro. Taken together, BcMF27 contributes to the intine morphogenesis during pollen development and stabilizes pollen tube elongation. This research can promote knowledge of PMEs function and the molecular mechanism in pollen wall construction.

The Arabidopsis thaliana Class II Formin FH13 Modulates Pollen Tube Growth

Formins are a large, evolutionarily conserved family of actin-nucleating proteins with additional roles in regulating microfilament, microtubule, and membrane dynamics. Angiosperm formins, expressed in both sporophytic and gametophytic tissues, can be divided into two subfamilies, Class I and Class II, each often exhibiting characteristic domain organization. Gametophytically expressed Class I formins have been documented to mediate plasma membrane-based actin assembly in pollen grains and pollen tubes, contributing to proper pollen germination and pollen tube tip growth, and a rice Class II formin, FH5/RMD, has been proposed to act as a positive regulator of pollen tube growth based on mutant phenotype and overexpression data. Here we report functional characterization of the Arabidopsis thaliana pollen-expressed typical Class II formin FH13 (At5g58160). Consistent with published transcriptome data, live-cell imaging in transgenic plants expressing fluorescent protein-tagged FH13 under the control of the FH13 promoter revealed expression in pollen and pollen tubes with non-homogeneous signal distribution in pollen tube cytoplasm, suggesting that this formin functions in the male gametophyte. Surprisingly, fh13 loss of function mutations do not affect plant fertility but result in stimulation of in vitro pollen tube growth, while tagged FH13 overexpression inhibits pollen tube elongation. Pollen tubes of mutants expressing a fluorescent actin marker exhibited possible minor alterations of actin organization. Our results thus indicate that FH13 controls or limits pollen tube growth, or, more generally, that typical Class II formins should be understood as modulators of pollen tube elongation rather than merely components of the molecular apparatus executing tip growth.

Ovary Signals for Pollen Tube Guidance in Chalazogamous Mangifera indica L.

Most flowering plants show porogamy in which the pollen tubes reach the egg apparatus through the micropyle. However, several species show chalazogamy, an unusual pollen tube growth, in which the pollen tubes reach the embryo sac through the chalaza. While ovary signals for pollen tube growth and guidance have been extensively studied in porogamous species, few studies have addressed the process in chalazogamous species such as mango (Mangifera indica L.), one of the five most important fruit crops worldwide in terms of production. In this study, we characterize pollen–pistil interaction in mango, paying special attention to three key players known to be involved in the directional pollen tube growth of porogamous species such as starch, arabinogalactan proteins (AGPs), and γ-aminobutyric acid (GABA). Starch grains were observed in the style and in the ponticulus at anthesis, but their number decreased 1 day after anthesis. AGPs, revealed by JIM8 and JIM13 antibodies, were homogenously observed in the style and ovary, but were more conspicuous in the nucellus around the egg apparatus. GABA, revealed by anti-GABA antibodies, was specifically observed in the transmitting tissue, including the ponticulus. Moreover, GABA was shown to stimulate in vitro mango pollen tube elongation. The results support the heterotrophic growth of mango pollen tubes in the style at the expense of starch, similarly to the observations in porogamous species. However, unlike porogamous species, the micropyle of mango does not show high levels of GABA and starch, although they were observed in the ponticulus and could play a role in supporting the unusual pollen tube growth in chalazogamous species.

The expression pattern of OsDim1 in rice and its proposed function

Development of plant tissues is dependent on numerous factors, including hormone activity, signaling, cell division, and elongation. In plants, Defective Entry into Mitosis 1 (Dim1) homologs are recognized as pivotal in leaf senescence and progress of normal growth, but their role in rice has not been functionally characterized. The findings presented in this paper suggest that OsDim1 is important in early seedling development, pollen tube elongation, and impacts rice yield components. The gene is expressed in the scutellum, endosperm, embryonic root, shoot, pollen grains and tubes, as well as in several organs of the rice flower. According to the present study findings, RNAi mediated knockdown of OsDim1 resulted in phytohormonal imbalance, reduced amylase activity, affected differentiation of embryonic root elongation zone tissues, suppressed embryonic root and shoot growth, and impaired pollen tube elongation. In contrast, overexpression of OsDim1 showed significant growth in embryonic roots and shoots, while it increased culm length, total number of tillers per plant, seed setting rate, and total number of grains per panicle compared to its wild type line. In summary, we propose OsDim1 plays an important role in seedling growth and pollen tube elongation, and has pleiotropic effects on reproductive tissues.