Abstract
The involvement of ethylene in fruit ripening is well documented, though knowledge regarding the crosstalk between ethylene and other hormones in ripening is lacking. We discovered that AUXIN RESPONSE FACTOR 2A (ARF2A), a recognized auxin signaling component, functions in the control of ripening. ARF2A expression is ripening regulated and reduced in the rin, nor and nr ripening mutants. It is also responsive to exogenous application of ethylene, auxin and abscisic acid (ABA). Over-expressing ARF2A in tomato resulted in blotchy ripening in which certain fruit regions turn red and possess accelerated ripening. ARF2A over-expressing fruit displayed early ethylene emission and ethylene signaling inhibition delayed their ripening phenotype, suggesting ethylene dependency. Both green and red fruit regions showed the induction of ethylene signaling components and master regulators of ripening. Comprehensive hormone profiling revealed that altered ARF2A expression in fruit significantly modified abscisates, cytokinins and salicylic acid while gibberellic acid and auxin metabolites were unaffected. Silencing of ARF2A further validated these observations as reducing ARF2A expression let to retarded fruit ripening, parthenocarpy and a disturbed hormonal profile. Finally, we show that ARF2A both homodimerizes and interacts with the ABA STRESS RIPENING (ASR1) protein, suggesting that ASR1 might be linking ABA and ethylene-dependent ripening. These results revealed that ARF2A interconnects signals of ethylene and additional hormones to co-ordinate the capacity of fruit tissue to initiate the complex ripening process.
Highlights
The significance of the gaseous hormone ethylene in the ripening of fleshy fruit has been recognized for almost sixty years [1]
We investigated the role of AUXIN RESPONSE FACTOR 2A (ARF2A) in tomato fruit ripening and suggest that it may be involved in the crosstalk between ethylene and other hormones
We show that overexpression of ARF2A (ARF2-OX) causes the fruit to ripen in an uneven, blotchy manner
Summary
The significance of the gaseous hormone ethylene in the ripening of fleshy fruit has been recognized for almost sixty years [1]. Mutants altered in pathways of hormone biosynthesis or signaling such as the auxin pathway mutant diageotropica (dgt) and the gibberellic acid (GA) pathway mutant parthenocarpic fruit (pat), provided evidence for the role of hormones other than ethylene in fruit development and ripening [8, 9]. These studies pointed towards the involvement of a multihormone signaling pathway in fruit ripening, for instance, tomato fruit with reduced ABA biosynthesis displayed reduced ethylene emission [10]. Auxin movement was shown to be inhibited in transgenic tomato plants with reduced levels of the ethylene receptor ETR1 [18]
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