RESEARCH SUMMARY

Recent work in our group has been focused in two separate topics.

First, we have continued the genetic dissection of storage protein trafficking to the vacuole in plants, through isolation of the mtv mutants impaired in this transport process. The first MTV gene isolated was isolated was VTI12, a SNARE protein that forms a complex at the TGN required for transport of storage proteins, but not of other vacuolar cargo. Other components of this pathway subsequently identified were an SM protein that positively regulates the VTI12 SNARE complex and the sorting receptors for storage proteins.

We are currently characterising other MTV proteins, such as MTV8, which contains a lipid-binding ENTH domain and is involved both in trafficking of storage proteins and in regulating plant senescence. Several of the genes isolated are co-expressed and are activated during the massive deposition of storage proteins that occurs in maturing-seed embryos, suggesting that they are induced by a common mechanism to achieve full transport capacity in those cells. We have initiated a project to identify the cis regulatory elements and trans-acting factors that activate their transcription during seed maturation. The goal is to develop tools to activate in vegetative tissues the expression en bloc of this (limiting) transport machinery and determine whether storage capacity is altered.

A second topic in the lab was initiated through isolation of the miniyo-1 (iyo-1) mutant, which has delayed organogenesis in the shoot apical meristem. Functional characterisation of MINIYO revealed that it is a necessary and sufficient factor for initiating all events of differentiation in Arabidopsis. Moreover, our results suggest that the targeted nuclear accumulation of IYO in transition cells functions as a transcriptional switch for this fate transition. We are now studying how endogenous and environmental signals regulate IYO expression and subcellular localization to control the onset of cell differentiation and, consequently, regulate plant growth and development.