The role of SYN1 in early Arabidopsis meiosis

Abstract

SYN1 is a meiosis-specific Arabidopsis homologue of yeast REC8. REC8 is an important component of the meiotic cohesion complex which maintains cohesion between sister chromatids. Cytological analysis of syn1$^{-/-}$ has shown chromosome fragmentation at metaphase I. To determine the basis of chromosome fragmentation in the syn1$^{-/-}$, three double mutants were constructed. I have demonstrated that chromosome fragmentation in syn1 is AtSPO11-1-dependent. Moreover, I have also shown that SYN1 has a role in DSB repair by analysing Atdmc1$^{-/-}$/syn1$^{-/-}$ meiocytes. To investigate this further, immunolocalization studies in wild-type and syn1$^{-/-}$ were conducted. Distribution of ASY1 and AtZYP1 was affected in syn1$^{-/-}$. Both proteins appeared as aggregates, developing into an abnormal short linear signal in early prophase I, suggesting that both axis formation and synapsis are compromised. Distribution of the recombination proteins AtRAD51 and AtMLH1 was also aberrant. Localization of SYN1 in wild-type nuclei revealed a continuous signal along the chromosome axes. However, careful inspection revealed that this was accompanied by patches of more intense signals, possibly corresponding to DSB regions. To investigate this further I analysed SYN1 distribution in an Atspo11-1-4$^{-/-}$ mutant. Whilst faint SYN1 signals were apparent along the axis, no patches of intense signals were visible. Cisplatin-induced DSBs restored AtZYP1 foci in Atspo11-1-4$^{-/-}$ and also resulted in restoration of intense patches of the SYN1 signals. This is consistent with the recruitment of SYN1 to DSB sites