The Phtheirospermum japonicum isopentenyltransferase PjIPT1a regulates host cytokinin responses in Arabidopsis

Abstract

The hemiparasitic plant Phtheirospermum japonicum is a nutritional specialist that supplements its nutrient requirements by parasitizing other plants through haustoria. During parasitism, the Phtheirospermum haustorium transfers hypertrophy-inducing cytokinins (CKs) to the infected host root. The CK biosynthesis genes required for haustorium-derived CKs and the induction of hypertrophy are still unknown. We searched for haustorium-expressed isopentenyltransferases (IPTs) that catalyse the first step of CK biosynthesis, confirmed the specific expression by in vivo imaging of a promoter-reporter, and further analysed the subcellular localization, the enzymatic function, and contribution to inducing hypertrophy by studying CRISPR-Cas9 induced Phtheirospermum mutants. PjIPT1a was specifically expressed in intrusive cells of the haustorium close to the host vasculature. PjIPT1a and its closest homolog PjIPT1b located to the cytosol and showed isopentenyltransferases activity in vitro with differences in substrate specificity. Mutating PjIPT1a abolished parasite-induced CK responses in the host. A homolog of PjIPT1a with shared characteristics was also identified in the related weed Striga hermonthica. With PjIPT1a we identified a bona fide parasitism gene. We propose that PjIPT1a exemplifies how parasitism-related functions evolve through gene duplications and neofunctionalization.

Strigolactones are chemoattractants for host tropism in Orobanchaceae parasitic plants

“…With the advent of genetic tools, including ethyl methyl sulfonate-driven mutagenesis and Agrobacterium rhizogenes-mediated root transformation 10,15,16 , P. japonicum has been used as a model Orobanchaceae species to investigate parasitism. These studies have revealed the molecular mechanisms regulating haustorium development, vasculature connection and exchange of molecules [12][13][14][16][17][18][19][20] . As a facultative parasite, P. japonicum does not require host-derived stimulants, such as SLs, for germination.…”