A Physcomitrella PIN protein acts in spermatogenesis and sporophyte retention

Abstract

SummaryThe auxin efflux PIN-FORMED (PIN) proteins are conserved in all land plants and important players in plant development. In the moss Physcomitrella (Physcomitrium patens) three canonical PINs (PpPINA-C) are expressed in the gametophore. PpPINA and PpPINB show functional activity in vegetative growth and sporophyte development. Here, we examined the role of PpPINC in the life cycle of Physcomitrella.We established reporter and knockout lines for PpPINC and analysed vegetative and reproductive tissues using microscopy and transcriptomic sequencing of moss gametangia.PpPINC is expressed in immature leaves, mature gametangia and during sporophyte development. The sperm cells (spermatozoids) of knockout mutants exhibit increased motility compared to the wild type and show an altered flagella phenotype. Further, the knockout mutants have a significantly increased fertility, and an increased abortion rate of premeiotic sporophytes.Here, we show that PpPINC is an important regulator for spermatogenesis and sporophyte development. We propose an evolutionary conserved way of polar growth during early moss embryo development and sporophyte attachment, while suggesting the mechanical function in sporophyte securement of a ring structure, the Lorch ring.