Dans un mode de réalisation, l’invention concerne le procédé de préparation et de détermination d’un altPEP tel que décrit précédemment, dans lequel ladite protéine est codée par un gène choisi parmi : Aae15 (Acyl-activating enzyme 15), Aae16 (AMP-dependent synthetase and ligase family protein), Abcg11 (White-brown complex-like protein), Abdcg34 (ABC transporter G family member 34), Acc1 (Acetyl-CoA Carboxylase), Agb1 (GTP binding protein beta 1), Als (Acetolactate synthase (chloroplastic)), Anac076 (NAC domain-containing protein 76), Apg9 (Autophagy 9), Arlb1 (GTP-binding protein 1), Arr1 (Two-component response regulator ARR1), Arr5 (Two-component response regulator ARR5), Arr6 (Two-component response regulator ARR6), At59 (Pectate lyase family protein), Bak1 (Brassinosteroid insensitive 1-associated receptor kinase 1), Bccp1 (Acetyl-CoA Carboxylase (chloroplastic) subunit 1), Bccp2 (Acetyl-CoA Carboxylase (chloroplastic) subunit 2), Bri1 (Brassinosteroid insensitive 1), Bzo2h3 (bZIP transcription factor family protein), Cesa6 (Cellulose synthase A catalytic subunit 6), Cipk3 (CBL-interacting protein kinase 3), Cks1 (Cyclin-dependent kinases regulatory subunit 1), Cobl8 (COBRA-like protein 8 precursor), Coi1 (Coronatine-insensitive protein 1), Cpk3 (Calcium-dependent protein kinase 3), Crk34 (Cysteine-rich receptor-like protein kinase 34), Cyp705a18 (Cytochrome P450, family 705, subfamily A, polypeptide 18), Cyp71b26 (Cytochrome P450, family 71, subfamily B, polypeptide 26), Cyp78a8 (Cytochrome P450, family 78, subfamily A, polypeptide 8), Cyp97b3 (Cytochrome P450, family 97, subfamily B, polypeptide 3), Dcl1 (Endoribonuclease Dicer homolog 1), Dur3 (Urea-proton symporter DUR3), Ein2 (Ethylene-insensitive protein 2), Emb175 (Pentatricopeptide repeat-containing protein), Emb2726 (Elongation factor Ts family protein), Emb9 (Dihydrofolate synthetase), Epsps (5-enolpyruvylshikimate-3-phosphate (chloroplastic)), Fnr1 (Ferredoxin-NADP[+]-oxidoreductase 1), Fve (Transducin family protein / WD-40 repeat family protein), Ga2ox7 (Gibberellin 2-beta-dioxygenase 7), Gapc (Glyceraldehyde-3-phosphate dehydrogenase), Gcn2 (ABC transporter family protein), Gdi2 (Guanosine nucleotide diphosphate dissociation inhibitor 2), Gln2 (Glutamine synthetase (chloroplastic)), Gsl3 (Callose synthase 2), Hag5 (Histone acetyltransferase of the MYST family 2), Hda18 (Histone deacetylase 18), Hexo1 (Beta-hexosaminidase 1), Hppd (4-hydroxyphenyl-pyruvate-dioxygenase), Hsl1 (B3 domain-containing transcription repressor VAL2), Iaa31 (Indole-3-acetic acid inducible 31), Iqd28 (IQ-domain 28), Jac1 (J-domain protein required for chloroplast accumulation response 1), Jar1 (Jasmonoyl--L-amino acid synthetase), Kp1 (Kinesin-like protein 1), Lrx2 (Leucine-rich repeat/extensin 2), Mapkkk3 (Mitogen-activated protein kinase kinase kinase 3), Mapkkk5 (Mitogen-activated protein kinase kinase kinase 5), Mfp2 (Multifunctional protein 2), Mrb1 (Transmembrane protein, putative (DUF3537)), Nsp1 (Nodulation signaling pathway 1), Pds (Phytoene desaturase (chloroplastic)), Pen3 (Phosphatidylinositol 3,4,5-trisphosphate 3-phosphatase and protein-tyrosine-phosphatase), Phyb (Phytochrome B), Pif3 (Phytochrome interacting factor 3), Pizza (Brassinosteroid-related acyltransferase 1), Ppox1 (Protoporphyrinogen oxidase (chloroplastic) 1), Ppox2 (Protoporphyrinogen oxidase (chloroplastic) 2), Prp39 (Tetratricopeptide repeat (TPR)-like superfamily protein), PsbA (Photosystem II D1 protein), Pskr1 (Phytosulfokin receptor 1), Rd21 (Granulin repeat cysteine protease family protein), Ring1 (RING/U-box superfamily protein), Ros1 (DNA glycosylase/AP lyase ROS1), Rpt4a (26S proteasome regulatory subunit 10B homolog A), Sfr6 (Mediator of RNA polymerase II transcription subunit 16), Shr (Protein SHORT-ROOT), Shy2 (Auxin-responsive protein IAA3), Skl (EIN2-like protein, nramp transporter), Sps1 (Sucrose phosphate synthase 2F), Spt (Transcription factor SPATULA), Stn8 (Serine/threonine-protein kinase), Tap46 (PP2A regulatory subunit TAP46), Topp6 (Serine/threonine-protein phosphatase PP1 isozyme 7), TubB6 (Tubulin), TubB8 (Tubulin), Uba1a (RNA-binding (RRM/RBD/RNP motifs) family protein), Vim3 (E3 ubiquitin-protein ligase), Sgr1 (Magnesium dechelatase), Abi5 (Abscisic acid (ABA)-insensitive 5), Hsp101 (Heat shock protein 101), Rh10 (ATP-dependent RNA helicase) et Wus (WUSCHEL).