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The calcium/calmodulin signal transduction system in appressorium differentiation of Colletotrichum trifolii
Abstract
Colletotrichum trifolii Bain and Essary is the causal agent of alfalfa anthracnose. Conidial germination and appressorial formation are important steps in the process of pathogenesis. These pre-penetration events, which begin with spore attachment and culminate with appressorial maturation, are prerequisite for penetration of host external barriers and subsequent colonization. This work is intended to assess the role of the Ca$\sp{2+}$/calmodulin signal transduction system during germination and appressorium development of C. trifolii. Initially, conditions were established for in vitro conidial germination and appressorium development in Colletotrichum trifolii, and the effects on these processes by modulating Ca$\sp{2+}$ and calmodulin by pharmacological agents are given. Results indicate that, as for other pathogenic fungi, appressorium development is induced on a hard surface. The data also suggest that disturbance of calcium homeostasis, by EGTA or calcium channel blocker, impairs appressorium development. Moreover, calmodulin inhibitors affect both germination and differentiation, implying that the Ca$\sp{2+}$/calmodulin signal transduction pathway is important in the early development of Colletotrichum trifolii on the plant host surface. In order to further investigate the role of calmodulin during differentiation, the unique calmodulin gene of C. trifolii was cloned, sequenced, and characterized. Sequence data show a gene with 7 exons, very similar to the calmodulin gene of N. crassa and A. nidulans. The protein coded by this gene is identical to the N. crassa calmodulin. Northern blot analysis showed that the calmodulin gene expression is higher during germination and appressorium development. To further investigate the role of calmodulin during C. trifolii development, a fragment of the calmodulin gene was cloned in an antisense orientation in front of the qa-2 promoter of N. crassa. Results showed that this promoter is functional, as calmodulin message was repressed. It is suggest that inhibition of calmodulin expression affected events of the fungal life development cycle, such as colony growth, germination, sporulation, and appressorium formation.
Subject Area
Molecular biology|Plant pathology|Microbiology
Recommended Citation
Warwar, Vitor, "The calcium/calmodulin signal transduction system in appressorium differentiation of Colletotrichum trifolii" (1995). ETD collection for University of Nebraska-Lincoln. AAI9600760.
https://digitalcommons.unl.edu/dissertations/AAI9600760