photo: Belinda Pratten/freeswimmers

It is possible to create water-efficient wheat varieties because plant traits contributing to transpiration efficiency have proved to be heritable. The School of Biology Environmental Biology group is currently focussing on understanding which genes are responsible for transpiration efficiency and how they operate.

Dr Josette Masle compared two strains of Arabidopsis that differed in a large number of molecular markers and which also differed in transpiration efficiency. By comparing these strains, a relevant genetic region was identified that contained ERECTA - a candidate gene. The team then assembled a population of Arabidopsis that comprised wild types and mutant plants that either lacked, or failed to express genes within the ERECTA family.

After undertaking a direct test for an ERECTA effect on transpiration efficiency, they then compared three erecta mutants with three lines that were essentially homozygous for the ERECTA allele. The ERECTA lines returned higher transpiration efficiency than the erecta mutants, by up to 20 percent. Significantly, the erecta mutant with lowest transpiration efficiency carried a null allele, and is characterised by an absence of ERECTA transcripts.

Spurred by that success, Dr Masle and her team next confirmed what had become a putative role for ERECTA in determining leaf transpiration efficiency. Over the past three years, they have transformed the null mutant and two additional mutants in different genetic backgrounds with a construct carrying the ERECTA allele. This particular construct was derived from a laboratory strain of Arabidopsis called Columbia. Resultant transgenic plants all expressed the typical ERECTA phenotype, and all returned higher transpiration efficiency. Comprehensive studies on further lines homozygous for the ERECTA transgene have confirmed that outcome and researchers in the Environmental Biology group are now investigating the underlying molecular and physiological mechanisms including leaf transpiration and photosynthesis.

The work of Josette Masle and her team has given a first clue into the genetic controls that influence transpiration efficiency by identifying a key gene family for the coordination of leaf photosynthesis and transpiration. With ERECTA identified as a locus driving plant attributes that contribute to overall transpiration efficiency, plant biologists now have in their hands a major tool for linking plant molecular biology with the quantitative genetics of a critical heritable trait, and its physiology.

Further Info Online:

• www.rsbs.anu.edu.au/Profiles/Josette_Masle