The effector PHYL1 from Candidatus Phytoplasma ziziphi induces abnormal floral development by destabilising flower development proteins.

Phytoplasmas can induce complex and substantial phenotypic changes in their hosts in ways that favour their colonisation, but the mechanisms underlying these changes remain largely unknown. Jujube witches' broom (JWB) disease is a typical phytoplasma disease causing great economic loss in Chinese jujube (Ziziphus jujuba Mill.). Here, we reported an effector, PHYL1 from Candidatus Phytoplasma ziziphi, which implicated in inducing abnormal floral organogenesis. Utilising a combination of in vivo and in vitro methods, we investigated the influence of PHYL1 on the proteins associated with floral development. Our findings reveal that PHYL1 facilitates the proteasome-mediated degradation of essential flower morphogenetic regulators, including AP1, SEP1, SEP2, SEP3, SEP4, CAL, and AGL6, through a distinctive pathway that is dependent on the activity of the 26S proteasome, thus obviating the requirement for lysine ubiquitination of the substrates. Further, the Y2H analysis showed that the leucine at position 75th in second α helix of PHYL1 is fundamental for the interactions of PHYL1 with AP1 and SEP1-4 in jujube and Arabidopsis. Our research carry profound implications for elucidating the contribution of PHYL1 to the aberrant floral development in diseased jujube, and help to establish a robust theoretical underpinning for the prophylaxis and therapy of JWB disease.