Reexamination of Chlorophyllase Function Implies Its Involvement in Defense against Chewing Herbivores

Abstract

Chlorophyllase (CLH) is a common plant enzyme that catalyzes the hydrolysis of chlorophyll to form chlorophyllide, a more hydrophilic derivative. For more than a century, the biological role of CLH has been controversial, although this enzyme has been often considered to catalyze chlorophyll catabolism during stress-induced chlorophyll breakdown. In this study, we found that the absence of CLH does not affect chlorophyll breakdown in intact leaf tissue in the absence or the presence of methyljasmonate, which is known to enhance stress-induced chlorophyll breakdown. Fractionation of cellular membranes shows that Arabidopsis (Arabidopsis thaliana) CLH is located in the endoplasmic reticulum and the tonoplast of intact plant cells. These results indicate that CLH is not involved in endogenous chlorophyll catabolism. Instead, we found that CLH promotes chlorophyllide formation upon disruption of leaf cells, or when it is artificially mistargeted to the chloroplast. These results indicate that CLH is responsible for chlorophyllide formation after the collapse of cells, which led us to hypothesize that chlorophyllide formation might be a process of defense against chewing herbivores. We found that Arabidopsis leaves with genetically enhanced CLH activity exhibit toxicity when fed to Spodoptera litura larvae, an insect herbivore. In addition, purified chlorophyllide partially suppresses the growth of the larvae. Taken together, these results support the presence of a unique binary defense system against insect herbivores involving chlorophyll and CLH. Potential mechanisms of chlorophyllide action for defense are discussed.

Identification of a Chlorophyll Dephytylase Involved in Chlorophyll Turnover in Arabidopsis

“…Recent work showed that Arabidopsis CLH1, the major isoform, is localized to the tonoplast and the endoplasmic reticulum, and artificially mistargeting CLH1 into chloroplasts causes Chlide accumulation and cell death (Hu et al, 2015), which suggests detrimental effects of the constitutive presence of CLH in chloroplasts. From these observations, we infer that CLD1 catalyzes a dephytylation reaction functionally distinct from that catalyzed by CLH.…”

“…CLH was shown to be involved in chlorophyll breakdown in postharvest citrus fruits and broccoli (Brassica oleracea var italica) florets (Azoulay Shemer et al, 2008;Chen et al, 2008) but not in senescent leaves and maturing seeds of Arabidopsis Zhang et al, 2014). The exact role of CLH in chlorophyll catabolism remains controversial, but it was shown to function in defense against pathogens and herbivores, which may disrupt the integrity of chloroplasts and render accessibility of chlorophyll to CLH (Kariola et al, 2005;Hu et al, 2015).…”

The Role of Specialized Photoreceptors in the Protection of Energy‐Rich Tissues

“…However, other evidence questions whether photosynthesis is genuinely suppressed during defense responses. Chlorophyll degradation itself may be a defensive strategy, as degradation products have anti-insect activity [56]. Other studies have shown that photosynthetic rates are not perturbed when defense responses are activated in the absence of physical damage, suggesting that some reports of decreased photosynthesis could be a consequence of physical damage (e.g., localized water loss from disrupted cells) [48,49,57].…”

Extra‐plastidial degradation of chlorophyll and photosystem I in tobacco leaves involving ‘senescence‐associated vacuoles’

“…Although for a long time chlorophyllase was thought to catalyze the first reaction of chlorophyll degradation in senescing leaves, current evidence shows that it has no role during senescence (Schenk et al, 2007) or during chlorophyll turnover in Arabidopsis seedlings subjected to heat shock (Lin et al, 2014). Instead, chlorophyllase participates in defense against necrotrophic bacteria (Kariola et al, 2005) and chewing insects (Hu et al, 2015). Chlorophyll dephytilase, another enzyme catalysing the removal of the phytol side chain of chlorophyll, is not expressed in senescing leaves (Lin et al, 2016).…”