Different Mechanisms Are Responsible for Chlorophyll Dephytylation during Fruit Ripening and Leaf Senescence in Tomato    

Abstract

Chlorophyll breakdown occurs in different green plant tissues (e.g. during leaf senescence and in ripening fruits). For different plant species, the PHEOPHORBIDE A OXYGENASE (PAO)/phyllobilin pathway has been described to be the major chlorophyll catabolic pathway. In this pathway, pheophorbide (i.e. magnesium-and phytol-free chlorophyll) occurs as a core intermediate. Most of the enzymes involved in the PAO/phyllobilin pathway are known; however, the mechanism of dephytylation remains uncertain. During Arabidopsis (Arabidopsis thaliana) leaf senescence, phytol hydrolysis is catalyzed by PHEOPHYTINASE (PPH), which is specific for pheophytin (i.e. magnesium-free chlorophyll). By contrast, in fruits of different Citrus spp., chlorophyllase, hydrolyzing phytol from chlorophyll, was shown to be active. Here, we enlighten the process of chlorophyll breakdown in tomato (Solanum lycopersicum), both in leaves and fruits. We demonstrate the activity of the PAO/phyllobilin pathway and identify tomato PPH (SlPPH), which, like its Arabidopsis ortholog, was specifically active on pheophytin. SlPPH localized to chloroplasts and was transcriptionally up-regulated during leaf senescence and fruit ripening. SlPPH-silencing tomato lines were impaired in chlorophyll breakdown and accumulated pheophytin during leaf senescence. However, although pheophytin transiently accumulated in ripening fruits of SlPPH-silencing lines, ultimately these fruits were able to degrade chlorophyll like the wild type. We conclude that PPH is the core phytol-hydrolytic enzyme during leaf senescence in different plant species; however, fruit ripening involves other hydrolases, which are active in parallel to PPH or are the core hydrolases in fruits. These hydrolases remain unidentified, and we discuss the question of whether chlorophyllases might be involved.

Phytochrome Interacting Factors (PIFs) in Solanum lycopersicum: Diversity, Evolutionary History and Expression Profiling during Different Developmental Processes

“…The leaves showed clear signs of senescence as evidenced by the reduction in chlorophyll content at the seventh day (S4A Fig). The degreening was explained by the increment in PHEOPHYTINASE expression, the enzyme responsible for chlorophyll dephytylation in tomato leaves [32] and accompanied by a reduction in SlGLK1 transcripts. Additionally, the induction of senescence was confirmed by the mRNA accumulation of the senescence marker SENESCENCE-ASSOCIATED GENE 12 ( SlSAG12 , [33]) and A .…”

“…Significant differences ( P <0.05) among treatments are indicated by asterisks. (b) Expression profile of GOLDEN 2-LIKE 1 ( SlGLK1 , involved in chloroplast development, [65]), SENESCENCE-ASSOCIATED GENE 12 ( SlSAG12 , late senescence marker, [32]), PHEOPHYTINASE ( SlPPH , involved in leaf chlorophyll degradation, [56]) and, three genes tomato genes homologs to the Arabidopsis thaliana ORESARA 1 ( SlORE1S02 , SlORE1S03 and SlORE1S06 , senescence-related transcription factor). Heatmap representation of the relative mRNA abundance compared to day 0.…”

Identification of a Chlorophyll Dephytylase Involved in Chlorophyll Turnover in Arabidopsis

“…Instead of dephytylation of chlorophyll a, chlorophyll breakdown in leaf senescence is mainly initiated by removing the magnesium ion from chlorophyll a to yield Phein a by Mg-dechelatase (Shimoda et al, 2016). Phein a is then dephytylated by pheophytinase (PPH), generating pheophorbide (Pheide) a for further degradation via the PHEOPHORBIDE A OXYGENASE pathway (Morita et al, 2009;Schelbert et al, 2009;Guyer et al, 2014). In contrast to CLH, recombinant PPH can dephytylate Pheins but not chlorophylls (Morita et al, 2009;Schelbert et al, 2009).…”

“…Thus, the enzyme responsible for removing the phytol chain from chlorophyll has remained elusive. Recently, PPH was found to be dispensable for chlorophyll breakdown during Arabidopsis seed maturation (Zhang et al, 2014) and tomato (Solanum lycopersicum) fruit ripening (Guyer et al, 2014), indicating the existence of an alternative dephytylating enzyme(s).…”

Regulação da biossíntese da vitamina E em tomateiro (Solanum lycopersicum L.): da diversidade natural à manipulação do metabolismo

“…Em tomateiro, Guyer et al (2014) recentemente mostraram que, em linhagens transgênicas silenciadas para PPH, embora a degradação de clorofila esteja comprometida durante a foliar senescência, os frutos ainda são capazes de degradar clorofila durante o amadurecimento. Os resultados sugerem a participação de outras hidrolases na defitilação da clorofila em frutos como as clorofilases ou outra(s) hidrolase(s) ainda não identificada(s) (Guyer et al, 2014).…”