The New Zealand Institute of Plant and Food Research , Private Bag 92169, Auckland 1142 , New Zealand ; School of Biological Sciences, University of Auckland , Private Bag 92019, Auckland 1142 , New Zealand.
AoB Plants. 2013;5:pls047. doi: 10.1093/aobpla/pls047. Epub 2013 Jan 17.
Fruit ripening is an important developmental trait in fleshy fruits, making the fruit palatable for seed dispersers. In some fruit species, there is a strong association between auxin concentrations and fruit ripening. We investigated the relationship between auxin concentrations and the onset of ethylene-related ripening in Malus × domestica (apples) at both the hormone and transcriptome levels.
Transgenic apples suppressed for the SEPALLATA1/2 (SEP1/2) class of gene (MADS8/9) that showed severely reduced ripening were compared with untransformed control apples. In each apple type, free indole-3-acetic acid (IAA) concentrations were measured during early ripening. The changes observed in auxin were assessed in light of global changes in gene expression.
It was found that mature MADS8/9-suppressed apples had a higher concentration of free IAA. This was associated with increased expression of the auxin biosynthetic genes in the indole-3-acetamide pathway. Additionally, in the MADS8/9-suppressed apples, there was less expression of the GH3 auxin-conjugating enzymes. A number of genes involved in the auxin-regulated transcription (AUX/IAA and ARF classes of genes) were also observed to change in expression, suggesting a mechanism for signal transduction at the start of ripening.
The delay in ripening observed in MADS8/9-suppressed apples may be partly due to high auxin concentrations. We propose that, to achieve low auxin associated with fruit maturation, the auxin homeostasis is controlled in a two-pronged manner: (i) by the reduction in biosynthesis and (ii) by an increase in auxin conjugation. This is associated with the change in expression of auxin-signalling genes and the up-regulation of ripening-related genes.
果实成熟是肉质果实的一个重要发育特征，使果实对种子传播者具有吸引力。在一些果实物种中，生长素浓度与果实成熟之间存在很强的关联。我们在激素和转录组水平上研究了苹果（Malus × domestica）中生长素浓度与乙烯相关成熟开始之间的关系。
我们比较了抑制 SEPALLATA1/2（SEP1/2）类基因（MADS8/9）表达的转基因苹果（表现出严重的成熟延迟）与未转化的对照苹果。在每种苹果类型中，在早期成熟过程中测量游离吲哚-3-乙酸（IAA）浓度。根据基因表达的整体变化评估生长素的变化。
发现成熟的 MADS8/9 抑制苹果具有较高浓度的游离 IAA。这与吲哚-3-乙酰胺途径中生长素生物合成基因的表达增加有关。此外，在 MADS8/9 抑制的苹果中，GH3 生长素结合酶的表达减少。还观察到参与生长素调节转录的许多基因（AUX/IAA 和 ARF 类基因）在表达上发生变化，这表明在成熟开始时存在信号转导机制。
在 MADS8/9 抑制的苹果中观察到的成熟延迟可能部分归因于生长素浓度高。我们提出，为了实现与果实成熟相关的低生长素，生长素稳态通过两种方式得到控制：（i）通过减少生物合成和（ii）通过增加生长素结合。这与生长素信号转导基因的表达变化以及成熟相关基因的上调有关。
