Functional interplay between protein kinase CK 2 and salicylic acid sustains PIN transcriptional expression and root development

• Published in: The Plant journal : for cell and molecular biology 2014-05, Vol.78 (3), p.411-423
• Main Authors: Armengot, Laia, Marquès‐Bueno, María Mar, Soria‐Garcia, Angel, Müller, Maren, Munné‐Bosch, Sergi, Martínez, María Carmen
• Format: Article
• Language: English
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/tpj.12481

We have previously reported that CK 2‐defective A rabidopsis thaliana plants ( CK 2mut plants) were impaired severely in root development and auxin polar transport, and exhibited transcriptional misregulation of auxin‐efflux transporters ( Plant J ., 67, 2011a, 169). In this work we show that CK 2mut roots accumulate high levels of salicylic acid ( SA ) and that the gene that encodes isochorismate synthase ( SID 2 ) is overexpressed, strongly suggesting that CK 2 activity is required for SA biosynthesis via the shikimate pathway. Moreover, SA activates transcription of CK 2‐encoding genes and, thus, SA and CK 2 appear to be part of an autoregulatory feed‐back loop to fine‐tune each other's activities. We also show that exogenous SA and constitutive high SA levels in cpr mutants reproduce the CK 2mut root phenotypes (decrease of root length and of number of lateral roots), whereas inhibition of CK 2 activity in SA ‐defective and SA ‐signalling mutants lead to less severe phenotypes, suggesting that the CK 2mut root phenotypes are SA ‐mediated effects. Moreover, exogenous SA mediates transcriptional repression of most of PIN ‐ FORMED ( PIN ) genes, which is the opposite effect observed in CK 2mut roots. These results prompted us to propose a model in which CK 2 acts as a link between SA homeostasis and transcriptional regulation of auxin‐efflux transporters. We also show that CK 2 overexpression in A rabidopsis has neither impact on SA biosynthesis nor on auxin transport, but it improves the Arabidopsis root system. Thus, unlike the outcome in mammals, an excess of CK 2 in plant cells does not produce neoplasia, but it might be advantageous for plant fitness.