Abstract
Root–shoot communication has a critical role in plant adaptation to environmental stress. Grafting is widely applied to enhance the abiotic stress tolerance of many horticultural crop species; however, the signal transduction mechanism involved in this tolerance remains unknown. Here, we show that pumpkin- or figleaf gourd rootstock-enhanced cold tolerance of watermelon shoots is accompanied by increases in the accumulation of melatonin, methyl jasmonate (MeJA), and hydrogen peroxide (H2O2). Increased melatonin levels in leaves were associated with both increased melatonin in rootstocks and MeJA-induced melatonin biosynthesis in leaves of plants under cold stress. Exogenous melatonin increased the accumulation of MeJA and H2O2 and enhanced cold tolerance, while inhibition of melatonin accumulation attenuated rootstock-induced MeJA and H2O2 accumulation and cold tolerance. MeJA application induced H2O2 accumulation and cold tolerance, but inhibition of JA biosynthesis abolished rootstock- or melatonin-induced H2O2 accumulation and cold tolerance. Additionally, inhibition of H2O2 production attenuated MeJA-induced tolerance to cold stress. Taken together, our results suggest that melatonin is involved in grafting-induced cold tolerance by inducing the accumulation of MeJA and H2O2. MeJA subsequently increases melatonin accumulation, forming a self-amplifying feedback loop that leads to increased H2O2 accumulation and cold tolerance. This study reveals a novel regulatory mechanism of rootstock-induced cold tolerance.
Highlights
IntroductionPlants frequently face challenges from various environmental factors throughout their life cycle
As sessile organisms, plants frequently face challenges from various environmental factors throughout their life cycle
Pumpkin and figleaf gourd rootstocks induced cold tolerance in watermelon shoots We first compared the leaf phenotypes, Fv/Fm values, and relative electrical conductivity (REC) of watermelon plants grafted onto the rootstocks of watermelon (Cl/Cl), pumpkin (Cl/Cm), and figleaf gourd (Cl/Cf)
Summary
Plants frequently face challenges from various environmental factors throughout their life cycle. At the whole-organism level, root-to-shoot communication is crucial for the increased survival of plants under environmental stress. In many horticultural crop species, grafting is widely applied to enhance plant tolerance to various environmental stresses, such as soil-borne pathogens, salt, and low temperature. Grafting-induced plant tolerance is associated with the inherent resistance of rootstocks and some rootstock-sourced signals that are transported to shoots and subsequently regulate shoot responses[4]. Grafting is a useful tool to reveal the signaling mechanisms related to root–shoot communication. By using cucumber scions grafted onto heat-tolerant luffa rootstock, Li et al.[5] revealed that rootproduced ABA as a long-distance signal could alter the expression of heat shock protein (HSP) 70 and subsequently improve heat tolerance of the shoots
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