Phyllotactic regularity requires the Paf1 complex in Arabidopsis [RESEARCH ARTICLE]

Kateryna Fal, Mengying Liu, Assem Duisembekova, Yassin Refahi, Elizabeth S. Haswell, and Olivier Hamant

In plants, aerial organs are initiated at stereotyped intervals, both spatially (every 137 degrees in a pattern called phyllotaxis) and temporally (at prescribed time intervals called plastochron). To investigate the molecular basis of such regularity, mutants with altered architecture have been isolated. However, most of them only exhibit defects in plastochron and/or produce a new, albeit equally reproducible, phyllotactic pattern. This leaves open the question of a molecular control of phyllotaxis regularity. Here we show that phyllotaxis regularity depends on the function of VIP proteins, components of the PolII-associating factor 1 (Paf1) complex. Divergence angles between successive organs along the stem exhibited increased variance in vip3-1 and vip3-2 than in the WT, in two different growth conditions. Similar results were obtained with the weak vip3-6 allele and in vip6, a mutant for another Paf1c subunit. Mathematical analysis confirmed that these defects could not be explained solely by plastochron defects. Instead, increased variance in phyllotaxis in vip3 was observed at the meristem and related to defects in spatial patterns of auxin activity. Thus the regularity of spatial, auxin-dependent, patterning at the meristem requires Paf1c.

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