KNOX2 Genes Regulate the Haploid-to-Diploid Morphological Transition in Land Plants

Abstract

A Mossy Veil Land plants have two distinct generations: a haploid gametophyte responsible for producing the gametes, and a diploid sporophyte, that in most land plants is the dominant form observed. However, in mosses, a basal land plant, the primary biomass is composed of the haploid gametophyte. Sakakibara et al. (p. 1067 ; see the Perspective by Friedman ) analyzed loss-of-function mutants of KNOX2 (class 2 KNOTTED1-LIKE HOMEOBOX) genes in the moss Physcomitrella patens. Mutant plants exhibit apospory, where fertilization apparently occurs, but the normal sporophyte phase is bypassed and instead a diploid structure resembling a haploid gametophyte is produced. The results suggest that KNOX2 regulates the alternation of generations by suppressing the haploid body plan in the diploid phase.