Root-derived trans-zeatin cytokinin protects Arabidopsis plants against
photoperiod stress
Abstract
Recently, a novel type of abiotic stress caused by a prolongation of the
light period - coined photoperiod stress - has been described in
Arabidopsis. During the night after the prolongation of the light
period, stress and cell death marker genes are induced. The next day,
strongly stressed plants display a reduced photosynthetic efficiency and
leaf cells eventually enter programmed cell death. The phytohormone
cytokinin (CK) acts as a negative regulator of this photoperiod stress
syndrome. In this study, we show that Arabidopsis wild-type plants
increase the CK concentration in response to photoperiod stress.
Analysis of cytokinin synthesis and transport mutants revealed that
root-derived trans-zeatin (tZ)-type CKs protect against photoperiod
stress. The CK signaling proteins ARABIDOPSIS HISTIDINE PHOSPHOTRANSFER
PROTEIN 2 (AHP2), AHP3 and AHP5 and transcription factors ARABIDOPSIS
RESPONSE REGULATOR 2 (ARR2), ARR10 and ARR12 are required for the
protective activity of CK. Analysis of higher order B-type arr mutants
suggested that a complex regulatory circuit exists in which the loss of
ARR10 or ARR12 can rescue the arr2 phenotype. Together the results
revealed the role of root-derived CK acting in the shoot through the
two-component signaling system to protect from the negative consequences
of strong photoperiod stress.