Abstract
In maize (Zea mays L.), unilateral cross-incompatibility (UCI) is controlled by Gametophyte factors (Ga), including Ga1, Ga2, and Tcb1; however, the molecular mechanisms underpinning this process remain unexplored. Here, we report the pollination phenotype of an inbred line, 511L, which carries a near-dominant Ga2-S allele. We performed a high-throughput RNA sequencing (RNA-Seq) analysis of the compatible and incompatible crosses between 511L and B73, to identify the transcriptomic differences associated with Ga2-mediated UCI. An in vivo kinetics analysis revealed that the growth of non-self pollen tubes was blocked at the early stages after pollination in 511L, maintaining the UCI barrier in Ga2. In total, 25,759 genes were expressed, of which, 2063 differentially expressed genes (DEGs) were induced by pollination (G_GG, G_GB, B_BB, B_BG). A gene ontology (GO) enrichment analysis revealed that these genes were specifically enriched in functions involved in cell wall strength and pectic product modification. Moreover, 1839, 4382, and 5041 genes were detected to differentially express under same pollination treatments, including B_G, BG_GG, and BB_GB, respectively. A total of 1467 DEGs were constitutively expressed between the two inbred lines following pollination treatments, which were enriched in metabolic processes, flavonoid biosynthesis, cysteine biosynthesis, and vacuole functions. Furthermore, we confirmed 14 DEGs related to cell wall modification and stress by qRT-PCR, which might be involved in Ga2-S-mediated UCI. Our results provide a comprehensive foundation for the molecular mechanisms involved in silks of UCI mediated by Ga2-S.
Highlights
Maize (Zea mays L.) is a typical cross-pollinating crop with distinct male and female flowers on the same plant. Both selfing and crossing strategies are readily successful in most maize lines; certain lines fail to set seeds when pollinated with non-self pollen, hybridizing in only one direction
Among the 44 downregulated genes, the 10 most downregulated genes were annotated as members of the “Hsp20/alpha crystallin family”, which are involved in the response to heat, high light intensity, and protein folding, indicating that Hsp20-mediated signaling may contribute to the Ga2-S cross-incompatibility process (Figure 4C, Table S9)
Given that Ga2-S is constitutively expressed in 511L silks, we sought to identify the specific differentially expressed genes (DEGs) in different genetic backgrounds under same pollination treatments, including between the two genotypes (B_G), BG_GG, and BB_GB
Summary
Maize (Zea mays L.) is a typical cross-pollinating crop with distinct male and female flowers on the same plant. During pollen–pistil interactions, the pollen (or pollen tube) and pistil (or embryo sac) secrete cysteine-rich proteins and lipid transfer proteins to exert diverse functions [39,40], such as self-recognition in the self-incompatibility (SI) system via the male determinant S locus cysteine-rich protein (SCR) [41,42], or the guidance of female tissues to regulate pollen tube growth [43,44]. Other factors, such as rapid alkalinization factors (RALFs) 4 and 19, were reported to interact with the receptor-like kinase (RLK) Catharanthus roseus RLK1-like subfamily (CrRLK1L) to maintain pollen tube integrity [45,46]. No significant differences in the number of genes present in each of the above four categories were detected between the silks of B, BB, and BG, nor between the silks of G, GG, and GB
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