LOL2 and LOL5 loci control latex production by laticifer cells in Euphorbia lathyris

: Laticifers are specialized plant cells capable of indefinite elongation that ramify extensively and are responsible for latex biosynthesis and accumulation. However, the mechanisms underlying laticifer cell differentiation, growth and production of latex remain largely unknown. In a search for mutants showing enhanced accumulation of latex we identified two LOT OF LATEX (LOL) loci in Euphorbia lathyris. lol2 and lol5 mutants show enhanced production of latex contained within laticifer cells. The recessive lol2 mutant carries increased biosynthesis of the plant hormone jasmonoyl-isoleucine (JA-Ile) and therefore establishes a genetic link between jasmonic acid (JA) signaling and latex production in laticifers. Instead, heightened production of latex in lol5 plants obeys to enhanced proliferation of laticifer cells. Phylogenetic analysis of laticifer-expressed genes in E. lathyris and in two other latex-bearing species, Euphorbia corallioides and Euphorbia palustris, allowed the identification of canonical JA responsive elements present in the gene promoter regions of laticifer marker genes. Moreover, we identified that the hormone JA functions not as a morphogen for laticifer differentiation but as a trigger for the fill out of laticifers with latex and the associated triterpenoids. The identification of LOL loci represents a further step towards the understanding of mechanisms controlling latex production in laticifer cells.