The calcium sensor CBL7 is required for Serendipita indica -induced
growth stimulation in Arabidopsis thaliana, controlling defense against
the endophyte and K + homeostasis in the symbiosis
Abstract
Calcium (Ca 2+) is an important second messenger in
plants. The activation of Ca 2+ signaling cascades is
critical in the activation of adaptive processes in response to
perceived environmental stimuli, including biotic stresses. The
colonization of roots by the plant growth promoting endophyte
Serendipita indica involves the increase of cytosolic Ca
2+ levels in Arabidopsis thaliana. In this
study, we investigated transcriptional changes in Arabidopsis roots
during symbiosis with S. indica. RNA-seq profiling disclosed the
significant induction of CALCINEURIN B-LIKE 7 ( CBL7)
during early- and later phases of the interaction. Consistent with the
transcriptomics analysis, reverse genetic evidence and yeast two-hybrid
studies highlighted the functional relevance of CBL7 and tested the
involvement of a CBL7-CBL-INTERACTING PROTEIN KINASE 13 (CIPK13)
signaling pathway in the establishment of the mutualistic relationship
that promotes plant growth. The loss-of-function of CBL7
abolished the growth promoting effect of S. indica and affected
the colonization of the root by the fungus. The subsequent
transcriptomics analysis of cbl7 revealed the involvement of this
Ca 2+ sensor in activating plant defense responses.
Furthermore, we report on the contribution of CBL7 to potassium
transport in Arabidopsis. Triggered by the differential expression of a
small number of K + channels/transporter genes, we
analyzed K + contents in wild-type and cbl7
plants and observed a significant accumulation of K +
in root of cbl7 plants, while shoot tissues demonstrated K
+ depletion. Taken together, our work associates CBL7
with an important role in the mutual interaction between Arabidopsis and
S. indica and links the CBL7 Ca 2+ receptor
protein to K + transport.