microRNAs associated with phosphate starvation and secondary metabolism are down-regulated in Xylella fastidiosa-infected grapevine. Vitis vinifera

The xylem-limited bacterium Xylella fastidiosa (XF) is the causal agent of Pierce’s disease (PD) in grapes and is a major threat to fruit, nut, olive, and coffee groves. PD is vectored by xylem sap-sucking insects and vector feeding preferences for XF-infected vines and olfactory cues like secondary metabolites of host plants may be important for PD etiology. Obvious PD symptoms are anthocyanin (red pigment) accumulation in leaves at the scorched periphery and shriveling of berries that impacts fruit quality and yield. The etiology of pleiotropic symptoms such as matchstick petioles and green cane islands by XF is not understood. XF may exploit host miRNAs as a 'Trojan horse' to circumvent or derange innate pathogen immunity responses. Our working hypothesis is that phosphate- and sugar-regulated microRNAs (miRNAs), initially described in Arabidopsis and associated with host Pi derangement in citrus greening disease Huanglongbing (HLB), mediate pleiotropic PD symptoms by Post-Transcriptional Gene Silencing (PTGS) mechanisms including amplification by miR828-triggered production of phased small-interfering RNAs (phasi-RNAs).