Importance of methionine biosynthesis for Arabidopsis seed germination and seedling growth

Abstract

Proteomics of Arabidopsis seeds revealed the differential accumulation during germination of two housekeeping enzymes. The first corresponded to methionine synthase that catalyses the last step in the plant methionine biosynthetic pathway. This protein was present at low level in dry mature seeds, and its level was increased strongly at 1-day imbibition, prior to radicle emergence. Its level was not increased further at 2-day imbibition, coincident with radicle emergence. However, its level in 1-day imbibed seeds strongly decreased upon subsequent drying of the imbibed seeds back to the original water content of the dry mature seeds. The second enzyme corresponded to S-adenosylmethionine synthetase that catalyses the synthesis of S-adenosylmethionine from methionine and ATP. In this case, this enzyme was detected in the form of two isozymes with different pI and Mr. Both proteins were absent in dry mature seeds and in 1-day imbibed seeds, but specifically accumulated at the moment of radicle protrusion. Arabidopsis seed germination was strongly delayed in the presence of dl-propargylglycine, a specific inhibitor of methionine synthesis. Furthermore, this compound totally inhibited seedling growth. These phenotypic effects were largely alleviated upon methionine supplementation in the germination medium. The results indicated that methionine synthase and S-adenosylmethionine synthetase are fundamental components controlling metabolism in the transition from a quiescent to a highly active state during seed germination. Moreover, the observed temporal patterns of accumulation of these proteins are consistent with an essential role of endogenous ethylene in Arabidopsis only after radicle protrusion.

The Effect of α-Amanitin on the Arabidopsis Seed Proteome Highlights the Distinct Roles of Stored and Neosynthesized mRNAs during Germination

“…7B), thus reinforcing the good matching between the protein patterns revealed by coloration with silver nitrate (total proteome) and through the incorporation of radiolabeled Met into newly synthesized proteins (de novo proteome). Several of the protein spots whose de novo synthesis increased in the presence of a-amanitin could be assigned to known proteins from reference maps of Arabidopsis seed proteins (Gallardo et al, 2001(Gallardo et al, , 2002a(Gallardo et al, , 2002b. They are listed in Table IV.…”

“…160), which corresponds to the last enzyme in the Met biosynthetic pathway (Ravanel et al, 1998). This metabolic pathway is of paramount importance for Arabidopsis seed germination and seedling growth since seed germination was shown to be strongly delayed in the presence of DL-propargylglycine, a specific inhibitor of Met synthesis, while this compound totally inhibited seedling growth (Gallardo et al, 2002b).…”

“…The radiolabeled proteome in Figure 6A was compared with the total proteome obtained after silver staining of the same gels (see Fig. 7) and also with the reference maps established for the Arabidopsis seed proteome (Gallardo et al, 2001(Gallardo et al, , 2002a(Gallardo et al, , 2002b. These comparisons can provide a means to tentatively assign some of the [ 35 S]Met-labeled protein spots to proteins previously characterized by matrix-assisted laser-desorption ionization time of flight (MALDI-TOF) analysis, although we cannot rule out the possibility that at least some of the [ 35 S]Met-labeled spots corresponded to very low abundant proteins that co-migrated with more abundant proteins.…”

“…We have initiated a global study of Arabidopsis seed germination by proteomics (Gallardo et al, 2001(Gallardo et al, , 2002a(Gallardo et al, , 2002b; http://seed.proteome.free.fr). In the present work, we wished to characterize those proteins for which accumulation level can be affected by a-amanitin during germination, thereby allowing the identification of genes that are under transcriptional control during this process.…”

“…Although it is widely documented that, in addition to the storage proteins, mature dry seeds accumulate during maturation a number of proteins that are involved in various cellular processes such as DNA replication and transcription, translation, metabolism, or defense mechanisms (e.g. see Bewley and Black, 1994;Gallardo et al, 2001Gallardo et al, , 2002aGallardo et al, , 2002b, their role and functionality has not yet been thoroughly documented. It is also known that mature dry seeds contain mRNAs stored during maturation, also called long-lived mRNAs to indicate that they can survive desiccation and remain active in dry quiescent embryos.…”