Abstract
Flowering is the key process for the sexual reproduction in seed plants. In gramineous crops, the process of flowering, which includes the actions of both glume opening and glume closing, is directly driven by the swelling and withering of lodicules due to the water flow into and out of lodicule cells. All these processes are considered to be controlled by aquaporins, which are the essential transmembrane proteins that facilitate the transport of water and other small molecules across the biological membranes. In the present study, the evolution of aquaporins and their contribution to flowering process in plants were investigated via an integration of genome-wide analysis and gene expression profiling. Across the barley genome, we found that HvTIP1;1, HvTIP1;2, HvTIP2;3, and HvPIP2;1 were the predominant aquaporin genes in lodicules and significantly upregulated in responding to glume opening and closing, suggesting the importance of them in the flowering process of barley. Likewise, the putative homologs of the above four aquaporin genes were also abundantly expressed in lodicules of the other monocots like rice and maize and in petals of eudicots like cotton, tobacco, and tomato. Furthermore, all of them were mostly upregulated in responding to the process of floret opening, indicating a conserved function of these aquaporin proteins in plant flowering. The phylogenetic analysis based on the OneKP database revealed that the homologs of TIP1;1, TIP1;2, TIP2;3, and PIP2;1 were highly conserved during the evolution, especially in the angiosperm species, in line with their conserved function in controlling the flowering process. Taken together, it could be concluded that the highly evolutionary conservation of TIP1;1, TIP1;2, TIP2;3 and PIP2;1 plays important roles in the flowering process for both monocots and eudicots.
Highlights
Anthesis is the key process for the sexual reproduction in flowering plants
The phylogenetic analysis of these barley aquaporin proteins (AQPs) with those from Arabidopsis and rice revealed that barley AQPs could be clearly categorized into four clades, representing plasma membrane intrinsic proteins (PIPs), tonoplast intrinsic proteins (TIPs), NIPs, and small basic intrinsic proteins (SIPs) (Supplementary Figure 2A), including 16, 9, 11, and 2 members, respectively (Supplementary Figure 2B)
The motifs 2, 3, 6, and 9 existed in HvPIPs; the motif 5 only existed in the HvTIPs and HvNIPs; and the motif 8 was only present in HvPIP1
Summary
Anthesis is the key process for the sexual reproduction in flowering plants. Normally, expansion of petals leads to anthesis in eudicots. The action of glume opening and closing possesses great utilization values for the agricultural production. Glume opening is the basis of cross-pollination to utilize heterosis in crossbreeding of cereal crops (AbdelGhani et al, 2004; Zhang et al, 2016), which has made a great contribution to improving crop yield, quality, and tolerance to meet the demand of the increasing global population in the last few decades (Yu et al, 2020; Zhang et al, 2021). To make better use of hybrid technology in crop production, the main challenge is to ensure the efficient production of hybrid seeds, which is highly restricted by the variation in flowering synchrony of parental lines (Mondo et al, 2016b)
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