For example, mutations in the Wx gene and its regulator DULL cause low amylose ent and hence whole selleck chem Imatinib Mesylate opaque endosperm. The amylose extender mutant has reduced activity of branching enzyme II, causing alteration in the fine structure of grain amylopectin. The flo 2 floury endosperm mutant harbors mutations affecting rice branching enzyme I activity. The floury endo sperm 4 mutant and the sugary 1 mutant are defective in pyruvate orthophosphate dikinase and debranching enzymes activity respectively. The formation of grain chalkiness can also be influ enced by various external stresses during the grain filling stage. Temperatures higher than 26 C, for example, could easily cause chalky appearance and a reduction in grain weight.

Microscopic observation showed that, compared with the translucent portion of rice endosperm that ripened under normal temperature which were filled with densely packed and polygonal granules, the chalky portion of high temperature ripened grains were loosely packed with elliptical shaped starch granules containing air spaces which caused random light reflection and hence chalky appearance. These observations demonstrated that environmental stresses represent another major cause for grain chalki ness in rice. Furthermore, imaging on endosperm amy loplast development of various japonica and indica rice lines indicated that starch synthesis in the rice grain may involve complicated genetic networks. Pre vious studies have detected many major quantitative trait loci that may underlie chalkiness in rice, however, only few QTLs have been isolated and functionally analyzed.

Thus, the molecular mechan isms underlying the formation of rice grain endosperm chalkiness still remain poorly understood. In this study, we performed a comparative transcrip tome analysis of the caryopses of a near isogenic line CSSL50 1 and its low chalkiness parental line Asominori. Corroborated with the pheno typic and physico biochemical observations, our gen ome wide transcription analysis supports the notion that rice grain endosperm development is controlled by a delicate, but complex genetic network. Notably, several pathways related to signal transduction, cell rescue defense, transcription, protein degradation, carbohydrate metabolism and redox homeostasis were found to be predominant among the differentially expressed genes. Results Phenotypic and physiochemical properties of Asominori and CSSL50 1 grains CSSL50 1 is derived from the near isogenic line CSSL50 with a small substituted segment Anacetrapib of chromosome 8 from the original donor IR24 in the largely Asominori back ground. CSSL50 1 displays high chalkiness under normal field conditions whereas its parental line Asominori has normal grains.