Nonpathogenic Strains ofColletotrichum lindemuthianumTrigger Progressive Bean Defense Responses during Appressorium-Mediated Penetration

Abstract

The fungal bean pathogen Colletotrichum lindemuthianum differentiates appressoria in order to penetrate bean tissues. We showed that appressorium development in C. lindemuthianum can be divided into three stages, and we obtained three nonpathogenic strains, including one strain blocked at each developmental stage. H18 was blocked at the appressorium differentiation stage; i.e., no genuine appressoria were formed. H191 was blocked at the appressorium maturation stage; i.e., appressoria exhibited a pigmentation defect and developed only partial internal turgor pressure. H290 was impaired in appressorium function; i.e., appressoria failed to penetrate into bean tissues. Furthermore, these strains could be further discriminated according to the bean defense responses that they induced. Surprisingly, appressorium maturation, but not appressorium function, was sufficient to induce most plant defense responses tested (superoxide ion production and strong induction of pathogenesis-related proteins). However, appressorium function (i.e., entry into the first host cell) was necessary for avirulence-mediated recognition of the fungus.

Entry Mode–Dependent Function of an Indole Glucosinolate Pathway in Arabidopsis for Nonhost Resistance against Anthracnose Pathogens

“…Of note, Cgstimulated PEN2, PEN3, CYP79B2, and CYP81F2 expression was detectable even earlier, at 9 hpi ( Figure 5A), indicating that Arabidopsis perceives the attack on the leaf surface and mounts defense responses to the intruder prior to the initiation of invasive growth. This is consistent with previous work on nonpathogenic Colletotrichum lindemuthianum mutant strains, showing that on leaves of its host, Phaseolus vulgaris, the formation of nonfunctional appressoria (i.e., failure to grow inside plant cells) was sufficient to induce plant defense responses (oxidative burst and PR protein accumulation; Veneault-Fourrey et al, 2005).…”

Melanin Is Not Required for Turgor Generation but Enhances Cell-Wall Rigidity in Appressoria of the Corn Pathogen Colletotrichum graminicola

“…Melanized appressoria of M. oryzae accumulate solutes with an osmotic potential of up to 8.0 MPa, which is 30 to 70% higher than in appressoria of melanin-deficient mutants of this fungus (Dean 1997). Similarly, nonmelanized appressoria of C. lindemuthianum showed cell collapse at much lower osmolyte concentrations than melanized appressoria (Veneault-Fourrey et al 2005).…”

Differential protein expression in Colletotrichum acutatum: changes associated with reactive oxygen species and nitrogen starvation implicated in pathogenicity on strawberry

“…Rapid accumulation of ROS by the host, which was observed beneath the appressorial structures, is apparently caused by local mechanical pressure generated by the developing appressoria. In C. lindemuthianum , it was shown that appressorium maturation, but not function, is sufficient to induce most plant defence responses (Veneault‐Fourrey et al ., 2005). The presence of abundant ROS produced by the host to account for penetration failure has also been observed for Colletotrichum coccodes causing anthracnose disease in tomato.…”