Identification and changes of the drought-induced cysteine protease transcriptome in soybean (Glycine max) root nodules

The formation and lifespan of soybean root nodules is affected by drought-stress, compromising the nitrogen supply of soybean plants. Expression of nodule cysteine proteases, involved in the regulation of the bacterial symbiosis and leghemoglobin degradation, increases during nodule senescence. Changes in the root nodule transcriptome were studied under varying drought-stress conditions using RNA-seq to identify nodule cysteine proteases induced following exposure to drought-stress conditions. Eight cysteine proteases belonging to the C1 family (papain-like cysteine proteases) and three cysteine proteases belonging to the C13 family (legumains or vacuole processing enzymes (VPE)) were induced by drought-stress. Expression of one C1 cysteine protease, Glyma.10G207100, was highly induced during drought but not under natural nodule senescence. A possible function of one C13 cysteine protease (alpha 1-VPE-deficient), which was highly expressed in nodules under drought, was further investigated in Arabidopsis mutant plants. C13 mutant plants showed decreased C1 cysteine protease activity, had higher biomass and protein levels under stress conditions compared to wild-type plants. From our study we conclude that the C1 cysteine protease, Glyma.14G085800 will be a useful indicator for drought-induced premature senescence of soybean root nodules and that silencing of C13 cysteine proteases (VPEs) might be a strategy to reduce the consequences C1 cysteine protease activity during drought-stress.