AUTHOR=Li Beibei , Wang Ruolin , Wang Shiya , Zhang Jiang , Chang Ling 

TITLE=Diversified Regulation of Cytokinin Levels and Signaling During Botrytis cinerea Infection in Arabidopsis

JOURNAL=Frontiers in Plant Science

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.584042

DOI=10.3389/fpls.2021.584042

ISSN=1664-462X

ABSTRACT=<p>Cytokinins (CKs) can modulate plant immunity to various pathogens, but how CKs are involved in plant defense responses to the necrotrophic pathogen <italic>Botrytis cinerea</italic> is still unknown. Here, we found that <italic>B. cinerea</italic> infection induced transcriptional changes in multiple genes involved in the biosynthesis, degradation, and signaling of CKs, as well as their contents, in pathogen-infected <italic>Arabidopsis</italic> leaves. Among the CKs, the gene expression of <italic>CYTOKININ OXIDASE/DEHYDROGENASE 5</italic> (<italic>CKX5</italic>) was remarkably induced in the local infected leaves and the distant leaves of the same plant without pathogen inoculation. <italic>Cis</italic>-zeatin (<italic>c</italic>Z) and its riboside (<italic>c</italic>ZR) accumulated considerably in infected leaves, suggesting an important role of the <italic>cis</italic>-zeatin type of CKs in the plant response to <italic>B. cinerea</italic>. Cytokinin double-receptor mutants were more susceptible to <italic>B. cinerea</italic> infection, whereas an exogenous CK treatment enhanced the expression levels of defense-related genes and of jasmonic acid (JA) and ethylene (ET), but not salicylic acid (SA), resulting in higher resistance of <italic>Arabidopsis</italic> to <italic>B. cinerea</italic>. Investigation of CK responses to <italic>B. cinerea</italic> infection in the JA biosynthesis mutant, <italic>jar1-1</italic>, and ET-insensitive mutant, <italic>ein2-1</italic>, showed that CK signaling and levels of CKs, namely, those of isopentenyladenine (iP), isopentenyladenine riboside (iPR), and <italic>trans</italic>-zeatin (<italic>t</italic>Z), were enhanced in <italic>jar1-1</italic>-infected leaves. By contrast, reductions in iP, iPR, <italic>t</italic>Z, and <italic>t</italic>Z riboside (<italic>t</italic>ZR) as well as <italic>c</italic>ZR contents occurred in <italic>ein2-1</italic>-infected leaves, whose transcript levels of CK signaling genes were likewise differentially regulated. The <italic>Arabidopsis Response Regulator 5</italic> (<italic>ARR5</italic>) gene was upregulated in infected leaves of <italic>ein2-1</italic> whereas another type-A response regulator, <italic>ARR16</italic>, was significantly downregulated, suggesting the existence of a complex regulation of CK signaling via the ET pathway. Accumulation of the <italic>cis</italic>-zeatin type of CKs in <italic>B. cinerea</italic>-infected leaves depended on ET but not JA pathways. Collectively, our findings provide evidence that CK responds to <italic>B. cinerea</italic> infection in a variety of ways that are differently modulated by JA and ET pathways in <italic>Arabidopsis</italic>.</p>