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Characterisation of ethylene pathway components in non-climacteric capsicum.

Aizat WM, Able JA, Stangoulis JC, Able AJ - BMC Plant Biol. (2013)

Bottom Line: Even though capsicum is in the same family as the well-characterised climacteric tomato (Solanaceae), it is non-climacteric and does not ripen normally in response to ethylene or if harvested when mature green.Ethylene did not stimulate capsicum ripening but 1-methylcyclopropene treatment delayed the ripening of Breaker-harvested fruit.The differential expression of several ethylene pathway components during ripening and upon ethylene or 1-methylclopropene treatment suggests that the ethylene pathway may be regulated differently in non-climacteric capsicum compared to the climacteric tomato.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Agriculture, Food and Wine, Waite Research Institute, The University of Adelaide, Glen Osmond SA 5064, Australia. amanda.able@adelaide.edu.au.

ABSTRACT

Background: Climacteric fruit exhibit high ethylene and respiration levels during ripening but these levels are limited in non-climacteric fruit. Even though capsicum is in the same family as the well-characterised climacteric tomato (Solanaceae), it is non-climacteric and does not ripen normally in response to ethylene or if harvested when mature green. However, ripening progresses normally in capsicum fruit when they are harvested during or after what is called the 'Breaker stage'. Whether ethylene, and components of the ethylene pathway such as 1-aminocyclopropane 1-carboxylate (ACC) oxidase (ACO), ACC synthase (ACS) and the ethylene receptor (ETR), contribute to non-climacteric ripening in capsicum has not been studied in detail. To elucidate the behaviour of ethylene pathway components in capsicum during ripening, further analysis is therefore needed. The effects of ethylene or inhibitors of ethylene perception, such as 1-methylcyclopropene, on capsicum fruit ripening and the ethylene pathway components may also shed some light on the role of ethylene in non-climacteric ripening.

Results: The expression of several isoforms of ACO, ACS and ETR were limited during capsicum ripening except one ACO isoform (CaACO4). ACS activity and ACC content were also low in capsicum despite the increase in ACO activity during the onset of ripening. Ethylene did not stimulate capsicum ripening but 1-methylcyclopropene treatment delayed the ripening of Breaker-harvested fruit. Some of the ACO, ACS and ETR isoforms were also differentially expressed upon treatment with ethylene or 1-methylcyclopropene.

Conclusions: ACS activity may be the rate limiting step in the ethylene pathway of capsicum which restricts ACC content. The differential expression of several ethylene pathway components during ripening and upon ethylene or 1-methylclopropene treatment suggests that the ethylene pathway may be regulated differently in non-climacteric capsicum compared to the climacteric tomato. Ethylene independent pathways may also exist in non-climacteric ripening as evidenced by the up-regulation of CaACO4 during ripening onset despite being negatively regulated by ethylene exposure. However, some level of ethylene perception may still be needed to induce ripening especially during the Breaker stage. A model of capsicum ripening is also presented to illustrate the probable role of ethylene in this non-climacteric fruit.

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A proposed model for the ripening of non-climacteric capsicum. The ethylene pathway generally involves different isoforms of ACO and ACS to produce ethylene before it is perceived by ETR for other downstream responses. In tomato, System 1 ethylene production during development will be followed by System 2 ethylene production to induce climacteric ripening [8]. However, in non-climacteric capsicum ripening, System 2 may be absent based on the limited expression (dotted arrows) of certain System 2-associated isoforms such as CaACS2 and CaACO1 during ripening and upon ethylene treatment (compared to their homologue expression in tomato). The expression of CaACS1 and CaACO4 during capsicum ripening was associated with System 1 due to their significant reduction upon ethylene treatment at either or both G and B stages. This is in contrast to the CaACO4 homologue in tomato, LeACO4, which is a System 2-associated isoform [22]. Therefore System 1 may be predominantly operating in capsicum to produce the basal ethylene level (while inhibiting System 2 ethylene production). The basal ethylene level may be needed to maintain the rate of ETR turnover, particularly subfamily II CaETR4 and CaETR5, as ethylene perception removal (through 1-MCP treatment) severely affected the CaETR expression as well as other possible downstream CaACO and CaACS isoforms. These subfamily II CaETRs may become saturated, and perhaps together with ethylene independent pathways upon ripening onset, non-climacteric capsicum ripening could be initiated. The ethylene independent pathways may also involve some ripening regulators such as RIN transcription factors and their presence may induce the expression of CaACO4 upon ripening onset.
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Figure 6: A proposed model for the ripening of non-climacteric capsicum. The ethylene pathway generally involves different isoforms of ACO and ACS to produce ethylene before it is perceived by ETR for other downstream responses. In tomato, System 1 ethylene production during development will be followed by System 2 ethylene production to induce climacteric ripening [8]. However, in non-climacteric capsicum ripening, System 2 may be absent based on the limited expression (dotted arrows) of certain System 2-associated isoforms such as CaACS2 and CaACO1 during ripening and upon ethylene treatment (compared to their homologue expression in tomato). The expression of CaACS1 and CaACO4 during capsicum ripening was associated with System 1 due to their significant reduction upon ethylene treatment at either or both G and B stages. This is in contrast to the CaACO4 homologue in tomato, LeACO4, which is a System 2-associated isoform [22]. Therefore System 1 may be predominantly operating in capsicum to produce the basal ethylene level (while inhibiting System 2 ethylene production). The basal ethylene level may be needed to maintain the rate of ETR turnover, particularly subfamily II CaETR4 and CaETR5, as ethylene perception removal (through 1-MCP treatment) severely affected the CaETR expression as well as other possible downstream CaACO and CaACS isoforms. These subfamily II CaETRs may become saturated, and perhaps together with ethylene independent pathways upon ripening onset, non-climacteric capsicum ripening could be initiated. The ethylene independent pathways may also involve some ripening regulators such as RIN transcription factors and their presence may induce the expression of CaACO4 upon ripening onset.

Mentions: Overall, the limited level of ethylene produced in non-climacteric capsicum may be contributed by the rate limiting ACS activity which restricts the ACC content. Furthermore, several isoforms of ethylene-related genes were differentially expressed in capsicum, suggesting alternative regulation and the likelihood that ethylene production in non-climacteric ripening is predominantly by System 1 with System 2 being absent (summarised in Figure 6). Ethylene independent pathway(s) may also be present during capsicum ripening onset but some level of ethylene perception may still be needed for the induction of non-climacteric fruit ripening (Figure 6).


Characterisation of ethylene pathway components in non-climacteric capsicum.

Aizat WM, Able JA, Stangoulis JC, Able AJ - BMC Plant Biol. (2013)

A proposed model for the ripening of non-climacteric capsicum. The ethylene pathway generally involves different isoforms of ACO and ACS to produce ethylene before it is perceived by ETR for other downstream responses. In tomato, System 1 ethylene production during development will be followed by System 2 ethylene production to induce climacteric ripening [8]. However, in non-climacteric capsicum ripening, System 2 may be absent based on the limited expression (dotted arrows) of certain System 2-associated isoforms such as CaACS2 and CaACO1 during ripening and upon ethylene treatment (compared to their homologue expression in tomato). The expression of CaACS1 and CaACO4 during capsicum ripening was associated with System 1 due to their significant reduction upon ethylene treatment at either or both G and B stages. This is in contrast to the CaACO4 homologue in tomato, LeACO4, which is a System 2-associated isoform [22]. Therefore System 1 may be predominantly operating in capsicum to produce the basal ethylene level (while inhibiting System 2 ethylene production). The basal ethylene level may be needed to maintain the rate of ETR turnover, particularly subfamily II CaETR4 and CaETR5, as ethylene perception removal (through 1-MCP treatment) severely affected the CaETR expression as well as other possible downstream CaACO and CaACS isoforms. These subfamily II CaETRs may become saturated, and perhaps together with ethylene independent pathways upon ripening onset, non-climacteric capsicum ripening could be initiated. The ethylene independent pathways may also involve some ripening regulators such as RIN transcription factors and their presence may induce the expression of CaACO4 upon ripening onset.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
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Figure 6: A proposed model for the ripening of non-climacteric capsicum. The ethylene pathway generally involves different isoforms of ACO and ACS to produce ethylene before it is perceived by ETR for other downstream responses. In tomato, System 1 ethylene production during development will be followed by System 2 ethylene production to induce climacteric ripening [8]. However, in non-climacteric capsicum ripening, System 2 may be absent based on the limited expression (dotted arrows) of certain System 2-associated isoforms such as CaACS2 and CaACO1 during ripening and upon ethylene treatment (compared to their homologue expression in tomato). The expression of CaACS1 and CaACO4 during capsicum ripening was associated with System 1 due to their significant reduction upon ethylene treatment at either or both G and B stages. This is in contrast to the CaACO4 homologue in tomato, LeACO4, which is a System 2-associated isoform [22]. Therefore System 1 may be predominantly operating in capsicum to produce the basal ethylene level (while inhibiting System 2 ethylene production). The basal ethylene level may be needed to maintain the rate of ETR turnover, particularly subfamily II CaETR4 and CaETR5, as ethylene perception removal (through 1-MCP treatment) severely affected the CaETR expression as well as other possible downstream CaACO and CaACS isoforms. These subfamily II CaETRs may become saturated, and perhaps together with ethylene independent pathways upon ripening onset, non-climacteric capsicum ripening could be initiated. The ethylene independent pathways may also involve some ripening regulators such as RIN transcription factors and their presence may induce the expression of CaACO4 upon ripening onset.
Mentions: Overall, the limited level of ethylene produced in non-climacteric capsicum may be contributed by the rate limiting ACS activity which restricts the ACC content. Furthermore, several isoforms of ethylene-related genes were differentially expressed in capsicum, suggesting alternative regulation and the likelihood that ethylene production in non-climacteric ripening is predominantly by System 1 with System 2 being absent (summarised in Figure 6). Ethylene independent pathway(s) may also be present during capsicum ripening onset but some level of ethylene perception may still be needed for the induction of non-climacteric fruit ripening (Figure 6).

Bottom Line: Even though capsicum is in the same family as the well-characterised climacteric tomato (Solanaceae), it is non-climacteric and does not ripen normally in response to ethylene or if harvested when mature green.Ethylene did not stimulate capsicum ripening but 1-methylcyclopropene treatment delayed the ripening of Breaker-harvested fruit.The differential expression of several ethylene pathway components during ripening and upon ethylene or 1-methylclopropene treatment suggests that the ethylene pathway may be regulated differently in non-climacteric capsicum compared to the climacteric tomato.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Agriculture, Food and Wine, Waite Research Institute, The University of Adelaide, Glen Osmond SA 5064, Australia. amanda.able@adelaide.edu.au.

ABSTRACT

Background: Climacteric fruit exhibit high ethylene and respiration levels during ripening but these levels are limited in non-climacteric fruit. Even though capsicum is in the same family as the well-characterised climacteric tomato (Solanaceae), it is non-climacteric and does not ripen normally in response to ethylene or if harvested when mature green. However, ripening progresses normally in capsicum fruit when they are harvested during or after what is called the 'Breaker stage'. Whether ethylene, and components of the ethylene pathway such as 1-aminocyclopropane 1-carboxylate (ACC) oxidase (ACO), ACC synthase (ACS) and the ethylene receptor (ETR), contribute to non-climacteric ripening in capsicum has not been studied in detail. To elucidate the behaviour of ethylene pathway components in capsicum during ripening, further analysis is therefore needed. The effects of ethylene or inhibitors of ethylene perception, such as 1-methylcyclopropene, on capsicum fruit ripening and the ethylene pathway components may also shed some light on the role of ethylene in non-climacteric ripening.

Results: The expression of several isoforms of ACO, ACS and ETR were limited during capsicum ripening except one ACO isoform (CaACO4). ACS activity and ACC content were also low in capsicum despite the increase in ACO activity during the onset of ripening. Ethylene did not stimulate capsicum ripening but 1-methylcyclopropene treatment delayed the ripening of Breaker-harvested fruit. Some of the ACO, ACS and ETR isoforms were also differentially expressed upon treatment with ethylene or 1-methylcyclopropene.

Conclusions: ACS activity may be the rate limiting step in the ethylene pathway of capsicum which restricts ACC content. The differential expression of several ethylene pathway components during ripening and upon ethylene or 1-methylclopropene treatment suggests that the ethylene pathway may be regulated differently in non-climacteric capsicum compared to the climacteric tomato. Ethylene independent pathways may also exist in non-climacteric ripening as evidenced by the up-regulation of CaACO4 during ripening onset despite being negatively regulated by ethylene exposure. However, some level of ethylene perception may still be needed to induce ripening especially during the Breaker stage. A model of capsicum ripening is also presented to illustrate the probable role of ethylene in this non-climacteric fruit.

Show MeSH
Related in: MedlinePlus