A stable Leifsonia xyli subsp. xyli GFP‐tagged strain reveals a new colonization niche in sugarcane tissues

Abstract

Ratoon stunting disease (RSD), caused by the bacterium Leifsonia xyli subsp. xyli (Lxx), is one of the most economically important diseases of sugarcane worldwide. Because knowledge on the interaction of Lxx with its host at the microscopic level is limited, the development of tools to monitor Lxx during the colonization process could shed new light on the processes that control disease development. In this investigation, a transformation protocol was optimized and a mutant Lxx strain engineered that stably expressed the gfp gene in sugarcane tissues. In vitro, the growth of the mutant did not differ from that of the wild type. Also, plants inoculated with both strains showed comparable growth and development when analysed 180 days after inoculation (dai). Fluorescence microscopy of roots, stalks, meristems and leaf tissues of Lxx‐GFP‐inoculated plants was performed at 180 dai. In the leaves, Lxx‐tagged cells were observed within the xylem vessels as has been described before but, in addition, they were found in a new niche within the host tissues, in the mesophyll and in the bundle sheath cells surrounding the vascular system. This finding indicates that Lxx is able to move from the xylem to the parenchyma of the leaf cells. This first report of an Lxx mutant expressing a heterologous gene revealed that colonization of sugarcane by this pathogen is not limited to the xylem vessels as commonly reported.

The physiological characteristics and associated gene expression of sugar cane inoculated with Leifsonia xyli subsp. xyli

“…The bacterium Lxx is difficult to isolate and culture because its growth is very slow (Haapalainen, Mattinen, & Metzler, ). Previous studies have shown that this pathogen colonises xylem vessels, the mesophyll and bundle sheath cells surrounding the vascular system (Maramorosch, Plavsic‐Banjac, Bird, & Liu, ; Quecine et al., ). These bacteria are physically transmitted from infected to healthy plants during mechanical harvesting (Hoy & Grisham, ) and can also spread via the planting of infected seedcanes.…”

Activities of key enzymes in the C4 pathway and anatomy of sugarcane infected by Leifsonia xyli subsp . xyli

“…In 2016, a new niche for colonization of sugarcane by Lxx has been described. Green fluorescent protein‐labelled Lxx bacteria appeared not only in the xylem vessels, but also in the mesophyll cell (MC) and in the bundle sheath cells (BSC) surrounding the vascular system of infected sugarcane leaves (Quecine et al ). This finding indicates that Lxx is able to transpose from the xylem to the parenchyma of the leaf cells.…”

Identification of candidate resistance metabolites to <em>Leifsonia xyli</em> subsp. <em>xyli</em> in sugarcane through metabolomic profiling

“…It has no flagella and colonizes the xylem vessels and meristem cells (Brumbley et al 2004). Recent studies using Lxx-GFP cells showed that this bacterium also colonizes the mesophyll and the bundle sheath cells surrounding the vascular system (Quecine et al 2016). In vitro cultivation of Lxx is difficult and requires a complex growth medium due to its fastidious nature (Davis et al 1980).…”

“…xyli (Lxx), which colonizes the xylem vessels, the meristem (Brumbley et al 2004), and the mesophyll and the bundle sheath cells of the host (Quecine et al 2016). This disease has been described in all sugarcane growing regions (Young and Nock 2017) and it can result in yield losses up to 80%, depending on environmental conditions (Li et al 2014).…”

“…The disease is caused by Leifsonia xyli subsp. xyli, a gram-positive and nutritionally fastidious bacterium that so far has been found to colonize the xylem vessels and bundle sheath cells surrounding the vascular system of sugarcane (Quecine et al 2016;Young 2016b;Monteiro-Vitorello et al 2004b). Lxx is regarded as an obligatory endophytic organism that grows to parasitic levels depending on yet poorly understood biotic and abiotic factors (Zavaglia et al 2016).…”