Phytoplasma Effector SAP54 Hijacks Plant Reproduction by Degrading MADS-box Proteins and Promotes Insect Colonization in a RAD23-Dependent Manner

Abstract

The phytoplasma bacterial plant parasite depends on leafhopper insects to spread and propagate itself. This study reveals how phytoplasma subverts plant development to turn flowers into leaves and thus make its host more attractive to leafhoppers.

MADS-domain transcription factors and the floral quartet model of flower development: linking plant development and evolution

“…One characteristic phenotype ('phyllody') of phytoplasma-infected plants from diverse species, including A. thaliana, resembles the phenotype of class E floral homeotic mutants, with floral organs unable to develop proper floral organ identity. This was recently shown to be due to proteasome-mediated degradation of the class A and E floral homeotic proteins AP1, CAULIFLOWER (CAL) and SEP3, which is initiated by interaction of the floral homeotic proteins with phytoplasma-secreted effector proteins termed SAP54 or PHYL1 (Maejima et al, 2014;MacLean et al, 2014). An in silico study suggests that the PHYL1 structure resembles that of the K domain, thus facilitating dimerization between some floral homeotic proteins and PHYL1 (Rümpler et al, 2015).…”

MicroRNA396-Targeted SHORT VEGETATIVE PHASE Is Required to Repress Flowering and Is Related to the Development of Abnormal Flower Symptoms by the Phyllody Symptoms1 Effector

“…Moreover, the miRNA expression patterns of PHYL1 plants (PHYL1 of PnWB) were also consistent with those of SAP54 plants. SAP54 and PHYL1 of onion yellows phytoplasma plants mediate AtAP1, AtSEP3, and AtCAL proteasomal degradation (MacLean et al, 2014;Maejima et al, 2014); therefore, MTF degradation might result in abnormal miRNA expression. These results indicate that these effectors contain common motif(s) for triggering leafy flower formation and altering miRNA expression.…”

“…These MTFs are key regulators in floral development and were triggered by SAP54/ PHYL1-mediated ubiquitin/26S proteasomal degradation by interacting with the RADIATION SENSITIVE23 (RAD23) family, resulting in interference in floral homeotic gene expression levels (MacLean et al, 2014;Maejima et al, 2014). Consistently, the ap1 mutant, ap1/cal double mutant, and sep1/sep2/sep3/sep4 quadruple mutant manifest various types of leafy flower (e.g.…”

“…PHYL1 and SAP54 interact with MADS domain transcription factors (MTFs) in Arabidopsis, such as SEPALLATA3 (AtSEP3), APETALA1 (AtAP1), and CAULIFLOWER (AtCAL; MacLean et al, 2014;Maejima et al, 2014). These MTFs are key regulators in floral development and were triggered by SAP54/ PHYL1-mediated ubiquitin/26S proteasomal degradation by interacting with the RADIATION SENSITIVE23 (RAD23) family, resulting in interference in floral homeotic gene expression levels (MacLean et al, 2014;Maejima et al, 2014).…”

Degradation of class E MADS-domain transcription factors in Arabidopsis by a phytoplasmal effector, phyllogen

“…12,14,15 Phyllogens interact with and degrade some MADS TFs, including SEP3 of Arabidopsis. 15,16 However, it is unknown whether the other 3 class E proteins (SEP1, SEP2, and SEP4) of Arabidopsis are also degraded by phyllogens, though their interactions with a phyllogen were shown in a yeast 2-hybrid assay. 16 It is also interesting from the perspective of the phylogenetic differences between SEP Keywords: Arabidopsis, floral development, MADS transcription factors, phyllody, phyllogen, phytoplasma, SEPALLATA genes: in an evolutionary analysis of SEP gene sub-family, SEP3 and the other 3 SEP genes of Arabidopsis were divided into 2 different clades.…”