Analysis Of Carbohydrate Metabolism And Key Genes Expression In The Leaf Sheath Of Early Senescence Leaves (esl) Rice Mutant During Grain Filling Stage

To elucidate the contribution of flag leaf sheath to the grains development during the grain filling stage, change of carbohydrates contents and transcript level sof relative genes involved in carbohydrate metabolism were investigated in the flag leaf sheaths of two rice genotypes, including early senescence leaf (esl) rice mutant and its wild type. The results showed that the contents of starch and sucrose in the leaf sheath of esl mutant decreased with the progress of grain filling, but accumulated again in wild type at the late grain filling stage. At the molecular level, SUT1 and SUT4 were significantly expressed in the leaf sheaths of two genotypes. The expression of SUT4 in the leaf sheath of esl mutant was higher than wild type at the early grain filling stage, suggesting an important role in sucrose transportation at the early grain filling stage in the leaf sheath of esl mutant. The expressions of CIN1, SuSyl and SuSy2 were associated with the genotype-dependent sucrose degradation and fructose formation during the entire grain filling period. On the other hand, the high transcriptional level of Amy4A at the early grain filling stage favored the mobilization of starch in the leaf sheath of esl mutant. However, the transcriptional levels of starch synthesis genes, such as AGPS1, AGPS2a, AGPL1, AGPL2, AGPL3, GBSSⅡ, SSSⅠ, SSSⅡc, SSSⅢb and SSS Ⅵb, in the flag leaf sheath of esl mutant were lower than those of wild type. This suggested that starch synthesis in the flag leaf sheath of esl mutant was limited, whereas in wild type, high soluble sugar levels favored the expression of AGPS1 and AGPL1 at the late grain filling stage, resulting in starch re-accumulation in the flag leaf sheath. Thus, we concluded that the flag leaf sheath served as source tissue for developing grains and as sink tissue for source leaf in esl mutant and its wild type respectively, during the grain filling stage. The functional transition of flag leaf sheaths in rice was genotype-dependent, and was distinguishable in different source leaf rice cultivars.