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Probing the Unknowns in Cytokinin-Mediated Immune Defense in Arabidopsis with Systems Biology Approaches

Libertas Academica
Publication Date
  • Bioinformatics And Biology Insights
  • Volume: 2014
  • Issue: 8
  • Biology
  • Computer Science


35Bioinformatics and Biology insights 2014:8 Open Access: Full open access to this and thousands of other papers at Bioinformatics and Biology Insights Introduction The small molecule hormone cytokinin occurs in different N6 derivatives of adenines. It is indispensible for almost every aspect of plant growth and development. In Arabidopsis, the signal of cytokinin is conveyed by two-component signaling systems (TCS; all abbreviations in Table 1).1 The first com- ponent of this system is composed of membrane-spanning Arabidopsis histidine kinases (AHKs), which sense the bind- ing of cytokinin to its CHASE domain. AHKs are not only limited to plasma membrane but also located on endoplasmic reticulum (ER).2 The second component of TCS is provided by nuclear response regulators (Arabidopsis response regula- tors type-B (type-B ARRs)), which are linked to AHKs by Arabidopsis histidine phosphotransfer proteins (AHPs). The type-B ARRs are positive regulators of cytokinin signaling and are transcriptional activators of type-A ARRs. The latter inhibit cytokinin signaling.1,2 Cytokinin plays an important role in controlling various functions such as cell proliferation and differentiation, nodulation, nutrient acquisition, circadian rhythm, abiotic stress responses, light responses, senescence, and immunity as signaling outputs.1–3 The interplay between cytokinin and auxin as well as ethylene (Et) has already been established.4,5 However, efforts elucidating the crosstalk between cytokinin and immune pathways in plants are still lagging behind. Generally, plants defend themselves against biotrophic infections through salicylic acid (SA)-mediated resistance and deter necrotrophic pathogens through the jas- monic acid (JA) pathway.6 Enhanced plant cytokinin responses have been shown to enhance plant immunity against diverse pathogens such as biotrophs,7 hemi-biotrophs,8,9 as well as necrotrophs.9,10 We, therefore, hypothesize that cytokinin cell

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