G1-1 and LeG1-1/LeG1-2 genes are involved in meristem activation during breakage of dormancy and early germination in potato tubers and tomato seeds

To determine the role of genes in plant development, we have analysed the expression of G1-1, a gene isolated in potato tuber and of its tomato homologues LeG1-1 and LeG1-2. Expression of G1-1 in tuber increased in buds during the first stages of sprouting, whereas almost no transcript was found in the parenchyma. The highest levels of expression were detectable in sprouts and in developing sink leaves. In situ hybridization on potato tissues showed that the G1-1 transcript was mainly localized in shoot apical meristems, suggesting that the expression of this gene was correlated to meristem activity. LeG1-1 and LeG1-2 expression, measured at different stages of tomato seed germination showed its maximum after the primordial roots emerged from the teguments. High levels of transcript were found both in roots and hypocotyls of the seedlings. Indeed LeG1-1 and LeG1-2 transcript levels were low in meristematic structures formed in the in vitro cultured tomato hypocotyls and in explants of cotyledons. All these results suggest that G1-1 and its homologues, LeG1-1 and LeG1-2, may be involved in the maintenance of the sink function of potato tuber and tomato seed. In these organs, they are also responsible for activation and growth of pre-existing meristems, but not in their de novo formation.