Cereal cystatins delay sprouting and nutrient loss in tubers of potato, Solanum tuberosum.

Aurélie Munger,Marie-Aube Simon,Dominique Michaud,Marie-Claire Goulet,Moustafa Khalf

doi:10.1186/s12870-015-0683-2

Abstract

BackgroundRecent studies have reported agronomically useful ectopic effects for recombinant protease inhibitors expressed in leaves of transgenic plants, including improved tolerance to abiotic stress conditions and partial resistance to necrotrophic pathogens. Here we assessed the effects of these proteins on the post-dormancy sprouting of storage organs, using as a model potato tubers expressing cysteine protease inhibitors of the cystatin protein superfamily.ResultsSprout emergence and distribution, soluble proteins, starch and soluble sugars were monitored in tubers of cereal cystatin-expressing clones stored for several months at 4 °C. Cystatin expression had a strong repressing effect on sprout growth, associated with an apparent loss of apical dominance and an increased number of small buds at the skin surface. Soluble protein content remained high for up to 48 weeks in cystatin-expressing tubers compared to control (untransformed) tubers, likely explained by a significant stabilization of the major storage protein patatin, decreased hydrolysis of the endogenous protease inhibitor multicystatin and low cystatin-sensitive cysteine protease activity in tuber tissue. Starch content decreased after several months in cystatin-expressing tubers but remained higher than in control tubers, unlike sucrose showing a slower accumulation in the transgenics. Plantlet emergence, storage protein processing and height of growing plants showed similar time-course patterns for control and transgenic tubers, except for a systematic delay of 2 or 3 d in the latter group likely due to limited sprout size at sowing.ConclusionsOur data point overall to the onset of metabolic interference effects for cereal cystatins in sprouting potato tubers. They suggest, in practice, the potential of endogenous cysteine proteases as relevant targets for the development of potato varieties with longer storage capabilities.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0683-2) contains supplementary material, which is available to authorized users.

Highlights

Recent studies have reported agronomically useful ectopic effects for recombinant protease inhibitors expressed in leaves of transgenic plants, including improved tolerance to abiotic stress conditions and partial resistance to necrotrophic pathogens
Little is known about the endogenous targets of cystatins in planta, but the ectopic effects reported for these proteins, the large numbers of Cys protease-encoding genes in plant genomes [10] and the well established roles of Cys proteases in such key physiological processes as programmed cell death, senescence, defense and storage protein mobilization [12] make the regulation of these enzymes an interesting route for crop improvement
Comparable levels of oryzacystatin I (OCI) transcripts were found in the 5th leaf of lines K52 and K53, compared to undetectable levels in the 5th leaf of control line K used as parent for genetic transformation (Fig. 1a)

Summary

Introduction

Recent studies have reported agronomically useful ectopic effects for recombinant protease inhibitors expressed in leaves of transgenic plants, including improved tolerance to abiotic stress conditions and partial resistance to necrotrophic pathogens. We assessed the effects of these proteins on the post-dormancy sprouting of storage organs, using as a model potato tubers expressing cysteine protease inhibitors of the cystatin protein superfamily. Little is known about the endogenous targets of cystatins in planta, but the ectopic effects reported for these proteins, the large numbers of Cys protease-encoding genes in plant genomes [10] and the well established roles of Cys proteases in such key physiological processes as programmed cell death, senescence, defense and storage protein mobilization [12] make the regulation of these enzymes an interesting route for crop improvement. A gibberellin-induced up-regulation of Cys protease genes concomitant with the repression of cystatin genes leads, to a low cystatin::Cys protease balance favoring storage protein mobilization and plantlet growth [14, 17,18,19,20]

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Results

Conclusion