The Endosperm-Specific Expression of YUCCA Genes Enhances Rice Grain Filling

Grain filling is a crucial process that affects yield in rice(Oryza sativa L.).Auxin biosynthesis and signaling are closely related to rice yield;therefore,it is important to understand the effects of auxin biosynthesis on rice grain filling to improve crop yield.In this study,we used physiological and molecular strategies to identify the roles of auxin in rice grain filling.Exogenous application of auxin(IAA)or auxin analogues(2,4-D)to young spikelets and flag leaves improved the seed-setting rate and yield per spike.Furthermore,real-time quantitative PCR assays confirmed that nine members of the OsYUCCA family of auxin biosynthetic genes were upregulated during grain filling,implication that auxin biosynthesis plays a major role in grain development.The specific expression of either Arabidopsis AtYUCCA1 or OsYUCCA2 in the endosperm or leaves resulted in increased expression of OsIAA genes and auxin content of seeds,as well as increased grain filling and seed-setting rate.This result establishes that the auxin content in grains and leaves is important for grain development.Our findings further highlight the potential applications for improving rice yield by elevating targeted gene expression in specific tissues.

Genome-Wide Analysis and Expression Patterns of the YUCCA Genes in Maize

Auxin plays important roles in various aspects of plant growth and development （Zhao, 2010）. In Arabidopsis, a number of YUCCA （YUC） genes, which are involved in auxin biosyn- thesis, have been identified （Zhao et al., 2001; Woodward et al., 2005; Cheng et al., 2006, 2007; Kim et al., 2007; Chen et al., 2014）. YUC genes encode flavin monooxygenases （FMOs） that convert indole-3-pyruvate （IPA） to indole-3-acetic acid （IAA） （Zhao, 2012）. The Arabidopsis YUC family is comprised of 11 members （Zhao et al., 2001;

Auxin biosynthesis by the YUCCA6 flavin monooxygenase gene in woodland strawberry

Auxin has been regarded as the main signal molecule coordinating the growth and ripening of fruits in strawberry, the reference genomic system for Rosaceae. The mechanisms regulating auxin biosynthesis in strawberry are largely elusive. Recently, we demonstrated that two YUCCA genes are involved in flower and fruit development in cultivated strawberry. Here, we show that the woodland strawberry （Fragaria vesca L.） genome harbors nine loci for YUCCA genes and eight of them encode functional proteins. Transcription pattern in different plant organs was different for all eight FvYUCs. Functionality of the FvYUC6 gene was studied in transgenic strawberry over- expressing FvYUC6, which showed typical high-auxin pheno- types. Overexpression of FvYUC6 also delayed flowering and led to complete male sterility in F. vesta. Additionally, specific repression of FvYUC6 expression by RNA interference signifi- cantly inhibited vegetative growth and reduced plant fertility. The development of leaves, roots, flowers, and fruits was greatly affected in FvYUC6-repressed plants. Expression of a subset of auxin-responsive genes was well correlated with the changes of FvYUC6 transcript levels and free indole-3-acetic acid levels in transgenic strawberry. These observations are consistent with an important role of FvYUC6 in auxin synthesis, and support a main role of the gene product in vegetative and reproductive development in woodland strawberry.