Proteomic analysis of grapevine (Vitis vinifera L.) leaf changes induced by transition to autotrophy and exposure to high light irradiance.

UNLABELLED

Using a proteomics approach, we evaluated the response of heterotrophic and autotrophic leaves of grapevine when exposed to high light irradiation. From a total of 572 protein spots detected on two-dimensional gels, 143 spots showed significant variation caused by changes in the trophic state. High light treatment caused variation in 90 spots, and 51 spots showed variation caused by the interaction between both factors. Regarding the trophic state of the leaf, most of the proteins detected in the heterotrophic stage decreased in abundance when the leaf reached the autotrophic stage. Major differences induced by high light were detected in autotrophic leaves. In the high-light-treated autotrophic leaves several proteins involved in the oxidative stress response were up-regulated. This pattern was not observed in the high-light-treated heterotrophic leaves. This indicates that in these types of leaves other mechanisms different to the protein antioxidant system are acting to protect young leaves against the excess of light. This also suggests that these protective mechanisms rely on other sets of proteins or non-enzymatic molecules, or that differences in protein dynamics between the heterotrophic and autotrophic stages makes the autotrophic leaves more prone to the accumulation of oxidative stress response proteins.

BIOLOGICAL SIGNIFICANCE

Transition from a heterotrophic to an autotrophic state is a key period during which the anatomical, physiological and molecular characteristics of a leaf are defined. In many aspects the right functioning of a leaf at its mature stage depends on the conditions under what this transition occurs. This because apart of the genetic control, environmental factors like mineral nutrition, temperature, water supply, light etc. are also important in its control. Many anatomical and physiological changes have been described in several plant species, however in grapevine molecular data regarding changes triggered by this transition or by light stress are still scarce. In this study, we identify that the transition from heterotrophic to autotrophic state in grapevine triggers major changes in the leaf proteome, which are mainly related to processes such as protein synthesis, protein folding and degradation, photosynthesis and chloroplast development. With the exception of proteins involved in carbon fixation, that increased in abundance, most of the proteins detected during the heterotrophic stage decreased in abundance when the leaf reached its autotrophic stage. This is most likely because leaves have reached their full size and from now they have to work as a carbon source for sink organs located in other parts of the plant. Despite the potential control of this transition by light, to date, no studies using a proteomics approach have been conducted to gain a broader view of the effects of short-term high light stress. Our results indicate that short-term high light exposure has a major impact on the proteome of the autotrophic leaves, and trigger a differential accumulation of several proteins involved in the oxidative stress response. Surprisingly, heterotrophic leaves do not display this pattern which can be attributed to a lower sensitivity of these leaves to high light stimulus. In fact we discovered that heterotrophic leaves are more tolerant to light stress than autotrophic leaves. This finding is of high biological significance because it helps to understand how young leaves are able to evolve to autotrophy in areas where high light intensities are predominant. This also reveals in this type of leaves the existence of alternative mechanisms to address this stressful condition. These observations provide new insights into the molecular changes occurring during transition of leaves to autotrophy particularly when this transition occurs under high light intensities. This for example occurs during the springtime when the grapevine buds burst and the young leaves are suddenly exposed to high light intensities.