Abstract
Male gametogenesis in plants is tightly controlled and involves the complex and precise regulation of transcriptional reprogramming. Interactions between WRKY proteins and VQ motif-containing proteins are required to control these complicated transcriptional networks. However, our understanding of the mechanisms by which these complexes affect downstream gene expression is quite limited. In this study, we found that WRKY2 and WKRY34 repress MYB97, MYB101, and MYB120 expression during male gametogenesis. MYB expression was up-regulated in the wrky2-1 wrky34-1 vq20-1 triple mutant during male gametogenesis. The expression levels of six potential targets of the three MYBs increased the most in the wrky2-1 wrky34-1 vq20-1 triple mutant, followed by the wrky2-1 wrky34-1 double mutant, compared with in wild-type. Yeast one-hybrid and dual luciferase reporter assays indicated that WRKY2 and WRKY34 recognized the MYB97 promoter by binding to its W-boxes. MYB97 overexpression caused defects in pollen germination and pollen tube length, which impacted male fertility. Thus, WRKY2/34–VQ20 complexes appear to negatively regulate the expression of certain MYBs during plant male gametogenesis.
Highlights
IntroductionThe male gametophyte (pollen) delivers the male gametes (sperm nuclei) to the embryo sac for double fertilization (McCormick, 2004; Berger and Twell, 2011)
In flowering plants, the male gametophyte delivers the male gametes to the embryo sac for double fertilization (McCormick, 2004; Berger and Twell, 2011)
We examined the expression patterns of WRKY2, WRKY34, VQ20, MYB97, MYB101, and MYB120 during male gametogenesis using publicly availabe microarray data, and the data indicated that the WRKY34 and VQ20 expression patterns had opposite trends as those of the three MYBs during this process (Supplementary Figure S1)
Summary
The male gametophyte (pollen) delivers the male gametes (sperm nuclei) to the embryo sac for double fertilization (McCormick, 2004; Berger and Twell, 2011). The developmental phase consists of microsporogenesis and microgametogenesis (Sanders et al, 1999). During this phase, the uninucleate microspore undergoes pollen mitosis I to create bicellular pollen containing a large vegetative cell and a generative cell. The progamic phase initiates after the pollen grain lands on the stigma, and includes pollen germination, pollen tube growth through the transmitting tissue, sperm nuclei discharge into the embryo sac, and the fusion of the male and female gametes (Borg et al, 2009; Hafidh et al, 2016). The two WRKY–VQ Complexes Regulate MYBs phases are highly transcriptionally regulated (Honys and Twell, 2004; Rutley and Twell, 2015); little is known regarding the transcription factors involved in the temporal and spatial regulation of pollen development (Ma and Sundaresan, 2010; Berger and Twell, 2011; Hafidh et al, 2016)
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