Loss of a highly conserved sterile alpha motif domain gene (WEEP) results in pendulous branch growth in peach trees.

Plant shoots typically grow upward in opposition to the pull of gravity. However, exceptions exist throughout the plant kingdom. Most conspicuous are trees with weeping or pendulous branches. While such trees have long been cultivated and appreciated for their ornamental value, the molecular basis behind the weeping habit is not known. Here, we characterized a weeping tree phenotype in Prunus persica (peach) and identified the underlying genetic mutation using a genomic sequencing approach. Weeping peach tree shoots exhibited a downward elliptical growth pattern and did not exhibit an upward bending in response to 90° reorientation. The causative allele was found to be an uncharacterized gene, Ppa013325, having a 1.8-Kb deletion spanning the 5' end. This gene, dubbed WEEP, was predominantly expressed in phloem tissues and encodes a highly conserved 129-amino acid protein containing a sterile alpha motif (SAM) domain. Silencing WEEP in the related tree species Prunus domestica (plum) resulted in more outward, downward, and wandering shoot orientations compared to standard trees, supporting a role for WEEP in directing lateral shoot growth in trees. This previously unknown regulator of branch orientation, which may also be a regulator of gravity perception or response, provides insights into our understanding of how tree branches grow in opposition to gravity and could serve as a critical target for manipulating tree architecture for improved tree shape in agricultural and horticulture applications.

A brachytic dwarfism trait (dw) in peach trees is caused by a nonsense mutation within the gibberellic acid receptor PpeGID1c.

Little is known about the genetic factors controlling tree size and shape. Here, we studied the genetic basis for a recessive brachytic dwarfism trait (dw) in peach (Prunus persica) that has little or no effect on fruit development. A sequencing-based mapping strategy positioned dw on the distal end of chromosome 6. Further sequence analysis and fine mapping identified a candidate gene for dw as a non-functional allele of the gibberellic acid receptor GID1c. Expression of the two GID1-like genes found in peach, PpeGID1c and PpeGID1b, was analyzed. GID1c was predominantly expressed in actively growing vegetative tissues, whereas GID1b was more highly expressed in reproductive tissues. Silencing of GID1c in plum via transgenic expression of a hairpin construct led to a dwarf phenotype similar to that of dw/dw peaches. In general, the degree of GID1c silencing corresponded to the degree of dwarfing. The results suggest that PpeGID1c serves a primary role in vegetative growth and elongation, whereas GID1b probably functions to regulate gibberellic acid perception in reproductive organs. Modification of GID1c expression could provide a rational approach to control tree size without impairing fruit development.

Progress studies of drought-responsive genes in rice.

Rice (Oryza sativa L.), one of the most agronomically important crops, supplies staple food for more than half of the world's population, especially those living in developing countries. The intensively increasing world population has put a great burden on rice production. Drought as one of the major limiting factors for rice productivity has challenged researchers to improve both the water management system and rice characteristics. Biotechnology has assisted researchers to identify genes that are responsive toward drought. This review consolidates the recent studies that expose a number of drought-responsive genes in rice, which are potential candidates for development of improved drought-tolerant transgenic rice cultivars. In addition, examples are provided of how various drought-responsive genes, such as transcription factor and protein kinase encoding genes, were explored to engineer rice plants for enhanced drought tolerance using transgenic approach. Furthermore, the involvement of various phytohormones in regulation of drought response as well as the complexity of drought-responsive networks, which is indicated by the crosstalks with other stress-responsive networks such as cold and salt stresses, will be discussed. It is hoped that by understanding how rice responds to drought, crop performance can be stabilized and protected under water deficit conditions.

Activation of Arabidopsis MAPK kinase kinase (AtMEKK1) and induction of AtMEKK1-AtMEK1 pathway by wounding.

We have constructed a series of deletion mutants of Arabidopsis MAPK kinase kinase (AtMEKK1) and obtained a constitutively active mutant, AtMEKK1Delta166, which lacks in self-inhibitory sequence of N-terminal 166 amino acids but still has substrate specificity. AtMEKK1Delta166 predominantly phosphorylates AtMEK1, an Arabidopsis MAPKK, but not its double mutant (AtMEK1T218A/S224E), suggesting that Thr-218 and Ser-224 are the phosphorylation sites. In wounded seedlings, AtMEKK1 was activated and phosphorylated its downstream AtMEK1. Furthermore, analysis using anti-AtMEKK1 and anti-AtMEK1 antibodies revealed that the interaction between the two proteins was signal dependent. These results suggest the presence of AtMEKK1-AtMEK1 pathway induced by wounding.