The HD-Zip I transcription factor HaHB4 produces an increment in xylem vasculature by repressing the auxin transporter LAX2

MORENO-PIOVANO GS; MORENO JE; CABELLO JV; ARCE AL; CHAN RL

Foc do Iguazu

Congreso; IPMB 2015; 2015

HaHB4, anHDZIP type I protein from Helianthus annuus, improves agronomic traitsrelated to water deprivation in Arabidopsis and other crop transgenic plants.Ectopic expression of HaHB4 in Arabidopsis induces a complex phenotypeincluding improved water use efficiency, delayed senescence and enhancedresistance to herbivory. The molecular mechanism underlying HaHB4 technologyis largely unknown. Using a bioinformatic approach, we identified the auxininflux carrier LAX2 as part of a set of HaHB4-regulated geneswith the potential to modulate water use efficiency. LAX2 geneexpression is down-regulated in HaHB4 overexpressing plants both inmicroarray and qPCR experiments. Given the importance of vascular tissues inwater transport and considering that several HDZIP type III transcriptionfactors are involved in vascular development, we decided to explore the phenotypeof lax2 mutant plants. Two differentmutant alleles of LAX2 showed an increment in xylem vasculature,including both cell number and size. Concomitantly, Arabidopsis plantsectopically expressing HaHB4 showed an increment in both phloem andxylem vasculature. In consonance with the role of xylem in water transport, weobserved that lax2 mutants consume significantly less water during a mildwater stress treatment compared to the WT genotype. Taken together, theseobservations connect auxin transport to the enhanced water use efficiencyinduced by HaHB4 in Arabidopsis and other crop plants and report theability of this HDZIP I protein to modulate vascular development.