PIN 1 gene in tomato ( Solanum lycopersicum ) defines organ initiation

21 22 23 24. CC-BY 4.0 International license peer-reviewed) is the author/funder. It is made available under a The copyright holder for this preprint (which was not. Abstract 25 The spatiotemporal localization of the plant hormone auxin acts as a positional cue 26 during early leaf and flower organogenesis. One of the main contributors to auxin localization is 27 the auxin efflux carrier PIN-FORMED1 (PIN1). Phylogenetic analysis has revealed that PIN1 28 genes are split into two sister clades; PIN1 and the relatively uncharacterized Sister-Of-PIN1 29 (SoPIN1). In this paper we identify entire-2 as a loss-of-function SlSoPIN1a (Solyc10g078370) 30 mutant in Solanum lycopersicum. The entire-2 plants are unable to specify proper leaf initiation 31 leading to a frequent switch from the wild type spiral phyllotactic pattern to distichous and 32 decussate patterns. Leaves in entire-2 are large and less complex and the leaflets display 33 spatial deformities in lamina expansion, vascular development, and margin specification. During 34 sympodial growth in entire-2 the specification of organ position and identity is greatly affected 35 resulting in variable branching patterns on the main sympodial and inflorescence axes. To 36 understand how SlSoPIN1a functions in establishing proper auxin maxima we used the auxin 37 signaling reporter DR5::Venus to visualize differences in auxin localization between entire-2 and 38 wild type. DR5::Venus visualization shows a widening of auxin localization which spreads to 39 subepidermal tissue layers during early leaf and flower organogenesis, showing that SoPIN1 40 functions to focus auxin signaling to the epidermal layer. The striking spatial deformities 41 observed in entire-2 help provide a mechanistic framework for explaining the function of the 42 SoPIN1 clade in angiosperm species.