Deciphering the Responses of Root Border-Like Cells of Arabidopsis and Flax to Pathogen-Derived Elicitors    

Abstract

Plant pathogens including fungi and bacteria cause many of the most serious crop diseases. The plant innate immune response is triggered upon recognition of microbe-associated molecular patterns (MAMPs) such as flagellin22 and peptidoglycan. To date, very little is known of MAMP-mediated responses in roots. Root border cells are cells that originate from root caps and are released individually into the rhizosphere. Root tips of Arabidopsis (Arabidopsis thaliana) and flax (Linum usitatissimum) release cells known as "border-like cells." Whereas root border cells of pea (Pisum sativum) are clearly involved in defense against fungal pathogens, the function of border-like cells remains to be established. In this study, we have investigated the responses of root border-like cells of Arabidopsis and flax to flagellin22 and peptidoglycan. We found that both MAMPs triggered a rapid oxidative burst in root border-like cells of both species. The production of reactive oxygen species was accompanied by modifications in the cell wall distribution of extensin epitopes. Extensins are hydroxyproline-rich glycoproteins that can be cross linked by hydrogen peroxide to enhance the mechanical strength of the cell wall. In addition, both MAMPs also caused deposition of callose, a well-known marker of MAMP-elicited defense. Furthermore, flagellin22 induced the overexpression of genes involved in the plant immune response in root border-like cells of Arabidopsis. Our findings demonstrate that root borderlike cells of flax and Arabidopsis are able to perceive an elicitation and activate defense responses. We also show that cell wall extensin is involved in the innate immunity response of root border-like cells.

Reactive oxygen species and plant resistance to fungal pathogens

“…The chitin-elicited production of ROS and of H 2 O 2 in particular has been demonstrated in roots of M. truncatula and Arabidopsis (Kim et al, 2006;Nars et al, 2013;Plancot et al, 2013). Using an elicitor from Fusarium oxysporum, increased levels of superoxide and H 2 O 2 were also detected in the border-like cells of Arabidopsis and flax roots (Plancot et al, 2013).…”

“…For example, this method was used to detect the singlet oxygen in thylakoid membranes under photoinhibitory conditions or UV stress (Hideg et al, 1994(Hideg et al, , 1995. The singlet oxygen and superoxide anion radicals can be also detected and localised using dansyl-based fluorescence sensors such as DanePy or HO-1889-NH (Hideg et al, 2002) as well as a Singlet Oxygen Sensors Green (SOGS) (Flors et al, 2006;Plancot et al, 2013).…”

“…They consist in non-fluorescent molecules that become fluorescent when oxidised by ROS, and the emitted fluorescence can be observed by fluorimetry and/or by fluorescent microscopy, an advantage of such probes (Benikhlef et al, 2013;Bulgakov et al, 2012;Fester and Hause, 2005;Guo et al, 2010;Kolla et al, 2007;L'Haridon et al, 2011;Li et al, 2007;Liu et al, 2010;Ma et al, 2013;Peleg-Grossman et al, 2012;Plancot et al, 2013;Tada et al, 2004;Wen et al, 2008;Ye et al, 2013). Luminol or luminol analogues are sensitive chemiluminescent probes used to quantify a relative intensity of ROS by counting the emitted light with a luminometer, CDD camera or a scintillation counter (Dubreuil-Maurizi et al, 2010;Flury et al, 2013;Kunz et al, 2006;L'Haridon et al, 2011;Mersmann et al, 2010).…”

Root exudate ofSolanum tuberosumis enriched in galactose-containing molecules and impacts the growth ofPectobacterium atrosepticum

“…All plant species produce populations of border cells that vary in number, shape, size and activity (Hawes et al, 2003;Driouich et al, 2007Driouich et al, , 2012Endo et al, 2011;Plancot et al, 2013). Border cells synthesize and secrete a large variety of substances, among which are many defence-related molecules that contribute to root protection (Wen et al, 2007(Wen et al, , 2009Cannesan et al, 2011;Plancot et al, 2013;Driouich et al, 2013). These molecules also contribute to the composition of the mucilage that often encloses border cells and influences microbial dynamic and activity within the rhizosphere.…”

“…Root border cells are known to originate from the root cap meristem, to detach individually and be released within the external environment (Hawes et al, 2003(Hawes et al, , 2012. All plant species produce populations of border cells that vary in number, shape, size and activity (Hawes et al, 2003;Driouich et al, 2007Driouich et al, , 2012Endo et al, 2011;Plancot et al, 2013). Border cells synthesize and secrete a large variety of substances, among which are many defence-related molecules that contribute to root protection (Wen et al, 2007(Wen et al, , 2009Cannesan et al, 2011;Plancot et al, 2013;Driouich et al, 2013).…”