CELL SIGNALING AND GROWTH FACTORS IN DEVELOPMENT: FROM MOLECULES TO ORGANOGENESIS

By Q. GAORI

INTERESTINGLY, SOME MUTANTS WITH SMOOTH MARGINS AND NO SECONDARY LEA ? ETS, SUCH AS SF , FEATURE LATE INITIATION OF BASAL PRIMARY LEA ? ETS AND/OR INTERCALARY LEA ? ETS THIS EXEMPLI ? ES THE EXTREME DEVELOP- MENTAL ? EXIBILITY OF THE TOMATO LEAF IT REMAINS TO BE SEEN WHETHER THE LATE ORGANOGENIC ACTIVITY IS CONTINUOUS WITH THE EARLY ACTIVITY OR WHETHER IT REPRESENTS REACTIVATION OF THE ORGANOGENIC POTENTIAL TOMATO WIRY MUTANTS SHOW A GRADIENT OF LEAF-SHAPE ABERRATIONS, WITH MILDER PHENOTYPES IN EARLY LEAVES, AND VERY SEVERE PHENOTYPE IN LATE LEAVES TYPICAL WIRY LEAF PHENOTYPES INCLUDE ALMOST NORMAL LEAVES, NARROW LEAVES THAT ARE BROADER IN THEIR DISTAL PART, LEAVES WITH TRUMPET-SHAPE DISTAL PART, AND VERY NARROW, WIRY-LIKE LEAVES ( 81, 82 ) SEVERAL ALLELIC AND NONALLELIC MUTANTS WITH THE WIRY SYN- DROME HAVE BEEN DESCRIBED ( 10, 67 ) WIRY LEAVES SHOW REDUCED LAMINA AND REDUCED LEVELS OF LEAF COMPLEXITY, BUT OFTEN HAVE INCREASED NUMBER OF INTERCALARY LEA ? ETS THE TOMATO PHANTASTICA ( PHAN ) GENE (WHICH BELONGS TO THE ARP GROUP) IS EXPRESSED IN THE ADAXIAL SIDE OF THE DEVELOPING TOMATO LEAF, AND ITS DOWNREGULATION LED TO A WIRY -LIKE PHENOTYPE ( 55 ) FURTHERMORE, ANALYSIS OF MANY SPECIES REVEALED A CORRELATION BETWEEN PHAN EXPRESSION, THE INTEGRITY OF THE ADAXIAL DOMAIN, AND LEAF SHAPE THESE OBSERVATIONS SUGGEST THAT PROPER ADAXIAL– ABAXIAL POLARITY IS IMPORTANT FOR COMPOUND-LEAF DEVELOPMENT FURTHER RESEARCH IS REQUIRED TO UNDERSTAND THE ROLE OF LEAF POLARITY IN COMPOUND-LEAF DEVELOPMENT AS THE LEAF MARGIN IS DE ? NED BY THE JUXTAPOSITION BETWEEN THE ADAXIAL AND THE ABAXIAL DOMAINS OF THE LEAF, IT IS POSSIBLE THAT THE MAINTENANCE OF THE MARGINAL BLASTO- ZONE DEPENDS ON THE PRESERVATION OF THE ABAXIAL–ADAXIAL POLARITY IN AGREEMENT, ARABIDOPSIS YABBY GENES WERE IMPLICATED IN THE INTERPRETATION OF ABAXIAL–ADAXIAL POLARITY, THE SPECI ? CATION OF THE LEAF MARGIN, THE NEGATIVE REGULATION OF KNOXI GENES AND THE PROMO- TION OF DETERMINATE GROWTH IN THE LEAVES ( 3, 83 ) AS DISCUSSED ABOVE, MAINTAINING TRANSIENT PARTIALLY INDETERMINATE GROWTH IN THE TOMATO LEAF MARGIN ENABLES THE ORGANOGENESIS OF MARGINAL STRUCTURES SUCH AS LEA ? ETS AND LOBES FROM THE MARGINAL BLASTOZONE LEA ? ET PRIMORDIA THAT INITIATE FROM THE TOMATO LEAF MARGIN SUBSTANTIALLY RESEMBLE LEAF PRIMORDIA THAT INITIATE AT THE ? ANKS OF THE SAM, DESPITE THE VERY DIFFERENT DEVELOPMENTAL CONTEXT ( 1, 15, 84 ) IN AGREEMENT, SOME OF THE MECHANISMS THAT MEDIATE 3 THE INVOLVEMENT OF ADAXIAL–ABAXIAL POLARITY IN COMPOUND-LEAF DEVELOPMENT 4 SPECI ? CATION AND SEPARATION OF LEA ? ETS CELL SIGNALING AND GROWTH FACTORS IN DEVELOPMENT