Shading stress has become a worldwide phenomenon and can lead to rice (Oryza sativa L.) yield loss by decreasing the seed setting rate, which, in rice, depends primarily on spikelet fertility. However, little is known about the effect of shading stress on rice pollination and fertilisation processes. Here, a field experiment, spanning two years, was conducted using two rice varieties grown under full sunlight and 53% shading stress. Shading stress at the heading stage significantly decreased the anther dehiscence rate, and a mass of pollen grains remained in the anthers. Together with a reduction in the in vitro pollen germination rate and stigma exsertion rate, shading stress reduced both the number of pollen grains and the number of germinated pollen grains per stigma by 29.44–71.16% and 9.82–63.16%, respectively. This ultimately resulted in yield loss due to reduction in the fertilisation and seed setting rates. We assert that shading stress decreased the seed setting rate by inhibiting the pollination and fertilisation processes of rice, particularly anther dehiscence and pollen grain release. Therefore, future studies should focus on the mechanisms behind anther dehiscence reduction under shading stress.

In animals and plants, circRNAs regulate gene expression and act as sponges that inhibit the activity of microRNAs. This study aimed to determine how specific circRNAs are expressed in rice grains at different stages of grain filling, under normal and low light conditions. We extracted total RNA from rice grains under low and sufficient light conditions. Deep sequencing was performed using circRNA libraries, and bioinformatics tools were used to identify the circRNAs. In addition, we analyzed targeted messenger RNA functions using two databases to predict the processes involved in rice grain development, and we conducted real-time PCR on 15 of the circRNAs. During the grain development process, 8015 candidate circRNAs were isolated, among which the number of known circRNAs was 1661. We also found that the number of circRNAs changed with the time of development. Among them, six circRNAs acted as sponges that targeted more than two microRNAs at different stages of development, and these circRNAs showed a regulatory pattern consistent with the transcriptome sequencing results. However, no differential circRNA expression was found under different light treatments. These findings reveal a possible link between circRNA regulation and the expression of the functional genes associated with photosignal-mediated rice grain development.