Regulation of Pathogenic Spore Germination by CgRac1 in the Fungal Plant Pathogen Colletotrichum gloeosporioides

Abstract

Colletotrichum gloeosporioides is a facultative plant pathogen: it can live as a saprophyte on dead organic matter or as a pathogen on a host plant. Different patterns of conidial germination have been recognized under saprophytic and pathogenic conditions, which also determine later development. Here we describe the role of CgRac1 in regulating pathogenic germination. The hallmark of pathogenic germination is unilateral formation of a single germ tube following the first cell division. However, transgenic strains expressing a constitutively active CgRac1 (CA-CgRac1) displayed simultaneous formation of two germ tubes, with nuclei continuing to divide in both cells after the first cell division. CA-CgRac1 also caused various other abnormalities, including difficulties in establishing and maintaining cell polarity, reduced conidial and hyphal adhesion, and formation of immature appressoria. Consequently, CA-CgRac1 isolates were completely nonpathogenic. Localization studies with cyan fluorescent protein (CFP)-CgRac1 fusion protein showed that the CgRac1 protein is abundant in conidia and in hyphal tips. Although the CFP signal was equally distributed in both cells of a germinating conidium, reactive oxygen species accumulated only in the cell that produced a germ tube, indicating that CgRac1 was active only in the germinating cell. Collectively, our results show that CgRac1 is a major regulator of asymmetric development and that it is involved in the regulation of both morphogenesis and nuclear division. Modification of CgRac1 activity disrupts the morphogenetic program and prevents fungal infection.

Involvement of Botrytis cinerea Small GTPases BcRAS1 and BcRAC in Differentiation, Virulence, and the Cell Cycle

“…Thus, collectively, the genetic (mutant strains) and pharmacological data all support an association between BcRAC and cell cycle progression through mitosis. Our findings strengthen a small number of previous reports that hint at an association between RAC and the cell cycle: in the dimorphic fungus U. maydis, CDC42 and RAC affect cytokinesis (20), and in Colletotrichum gloeosporioides, modification of RAC leads to changes in the cell cycle and nuclear division (19). Interestingly, a multinucleated phenotype similar to the one observed in the CA-BcRAC strain (gain of function) was previously reported for B. cinerea BcCDC42 (38).…”

“…A small number of reports have connected RAC proteins with cell cycle progression (19,50,51). We used RAC-and cell cycleinhibitory compounds to address the possible role of BcRAC in germination and nuclear division.…”

“…For example, in A. nidulans, these small GTPases have been associated with control of hyphal morphogenesis and polarity establishment (18). In Colletotrichum gloeosporioides, CgRAC1 is associated with asymmetric development and with the regulation of morphogenesis, pathogenesis, and nuclear division (19). In Ustilago maydis, RAC and CDC42 regulate polarized growth, cytokinesis, and pathogenicity (20).…”

Transcriptome Profiling of Botrytis cinerea Conidial Germination Reveals Upregulation of Infection-Related Genes during the Prepenetration Stage

“…aeschynomenes (1), breaking of spore dormancy is often induced by surface contact stimuli, such as surface hardness and hydrophobicity, either alone or in combination with nutrient signals. Although some signal transduction components, such as cAMP, Ras2, and Rac1, have been found to be involved in the germination process of these fungi, the regulatory mechanisms are still poorly understood (1,9,10). After germination on appropriate surfaces such as host cuticles, germ tube elongation occurs until perception of physical and/or chemical stimuli by the germ tube tip, resulting in the cessation of germ tube elongation and appressorium formation (7,11,12,13,14,15).…”

Caracterización química y evaluación de la actividad antifúngica del aceite esencial foliar de Lippia alba contra Colletotrichum gloeosporioides

“…& H. Schrenk) es el agente causal de la antracnosis en diferentes plantas tropicales (Bussaman et al 2012). Es un hongo facultativo, ya que puede vivir como saprofito o como patógeno en una planta (Nesher et al 2011). Dentro del género Colletotrichum se encuentran especies que causan importantes enfermedades en un amplio rango de plantas las cuales incluyen legumbres, cereales, verduras y frutos cultivables (Talhinhas et al 2005).…”