Abstract
KLU, encoded by a cytochrome P450 CYP78A family gene, generates an important—albeit unknown—mobile signal that is distinct from the classical phytohormones. Multiple lines of evidence suggest that KLU/KLU-dependent signaling functions in several vital developmental programs, including leaf initiation, leaf/floral organ growth, and megasporocyte cell fate. However, the interactions between KLU/KLU-dependent signaling and the other classical phytohormones, as well as how KLU influences plant physiological responses, remain poorly understood. Here, we applied in-depth, multi-omics analysis to monitor transcriptome and metabolome dynamics in klu-mutant and KLU-overexpressing Arabidopsis plants. By integrating transcriptome sequencing data and primary metabolite profiling alongside phytohormone measurements, our results showed that cytokinin signaling, with its well-established function in delaying leaf senescence, was activated in KLU-overexpressing plants. Consistently, KLU-overexpressing plants exhibited significantly delayed leaf senescence and increased leaf longevity, whereas the klu-mutant plants showed early leaf senescence. In addition, proline biosynthesis and catabolism were enhanced following KLU overexpression owing to increased expression of genes associated with proline metabolism. Furthermore, KLU-overexpressing plants showed enhanced drought-stress tolerance and reduced water loss. Collectively, our work illustrates a role for KLU in positively regulating leaf longevity and drought tolerance by synergistically activating cytokinin signaling and promoting proline metabolism. These data promote KLU as a potential ideal genetic target to improve plant fitness.
Highlights
As sessile organisms, plants have several adaptive mechanisms allowing them to cope with fluctuating environmental conditions
MA plots showed that a high number of differentially expressed genes (DEGs) were detected when comparing KLU-overexpression lines with both WT and the klu mutants, whereas very few DEGs were found between WT and klu (Figure 1, D, Supplemental Figure S1, A, and Supplemental Table S1)
Reverse transcription quantitative PCR (RT-qPCR) revealed that the expression levels of several other members of this family were increased in the klu mutant, whereas they were decreased in 35S:KLU1 plants (Supplemental Figure S1, C)
Summary
Plants have several adaptive mechanisms allowing them to cope with fluctuating environmental conditions. Leaf senescence greatly increases plant fitness, reproduction, and survival by actively recycling nutrients and energy from old leaves into newly developing organs or offspring (Yoshida, 2003; Lim et al, 2007). Leaf senescence occurs in an age-dependent manner, and its related processes, including chlorophyll degradation and programmed cell death, are finely tuned by the Received October 07, 2020.
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