Protein ubiquitination is a very diverse post-translational modification leading to protein degradation or delocalization, or altering protein activity. In Arabidopsis thaliana, two E3 ligases, BIG BROTHER (BB) and DA2, activate the latent peptidases DA1, DAR1 and DAR2 by mono-ubiquitination at multiple sites. Subsequently, these activated peptidases destabilize various positive regulators of growth. Here, we show that two ubiquitin-specific proteases, UBP12 and UBP13, deubiquitinate DA1, DAR1 and DAR2, hence reducing their peptidase activity. Overexpression of UBP12 or UBP13 strongly decreased leaf size and cell area, and resulted in lower ploidy levels. Mutants in which UBP12 and UBP13 were downregulated produced smaller leaves that contained fewer and smaller cells. Remarkably, neither UBP12 nor UBP13 were found to be cleavage substrates of the activated DA1. Our results therefore suggest that UBP12 and UBP13 work upstream of DA1, DAR1 and DAR2 to restrict their protease activity and hence fine-tune plant growth and development.

中文翻译：

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UBP12和UBP13负调控泛素依赖性肽酶DA1，DAR1和DAR2的活性

蛋白质泛素化是一种非常多样化的翻译后修饰，可导致蛋白质降解或异位，或改变蛋白质活性。在拟南芥中，两个E3连接酶BIG BROTHER（BB）和DA2通过在多个位点单泛素化激活潜在的肽酶DA1，DAR1和DAR2。随后，这些活化的肽酶使各种生长的正调节剂不稳定。在这里，我们显示了两个泛素特异性蛋白酶UBP12和UBP13使泛素作用于DA1，DAR1和DAR2，从而降低了它们的肽酶活性。UBP12或UBP13的过表达强烈降低了叶的大小和细胞面积，并导致较低的倍性水平。UBP12和UBP13的突变体被下调的植物产生的叶子越来越小，其中的细胞越来越少。显着地，未发现UBP12和UBP13都不是活化的DA1的切割底物。因此，我们的结果表明，UBP12和UBP13在DA1，DAR1和DAR2的上游起作用，以限制其蛋白酶活性，从而微调植物的生长发育。