A single amino acid substitution in MdLAZY1A dominantly impairs shoot gravitropism in Malus

Abstract

Plant architecture is one of the most important factors that determines crop yield potential and productivity. In apple (Malus domestica), genetic improvement of tree architecture has been challenging due to a long juvenile phase and growth as complex trees composed of a distinct scion and a rootstock. To better understand the genetic control of apple tree architecture, the dominant weeping growth phenotype was investigated. We report the identification of MdLAZY1A (MD13G1122400) as the genetic determinant underpinning the Weeping (W) locus that largely controls weeping growth in Malus. MdLAZY1A is one of the four paralogs in apple that are most closely related to AtLAZY1 involved in gravitropism in Arabidopsis (Arabidopsis thaliana). The weeping allele (MdLAZY1A-W) contains a single nucleotide mutation c.584T > C that leads to a leucine to proline (L195P) substitution within a predicted transmembrane domain that co-localizes with Region III, one of the five conserved regions in LAZY1-like proteins. Subcellular localization revealed that MdLAZY1A localizes to the plasma membrane and nucleus in plant cells. Over-expressing the weeping allele in apple cultivar Royal Gala (RG) with standard growth habit impaired its gravitropic response and altered the growth to weeping-like. Suppressing the standard allele (MdLAZY1A-S) by RNA interference (RNAi) in RG similarly changed the branch growth direction to downward. Overall, the L195P mutation in MdLAZY1A is genetically causal for weeping growth, underscoring not only the crucial roles of residue L195 and Region III in MdLAZY1A-mediated gravitropic response, but also a potential DNA base editing target for tree architecture improvement in Malus and other crops.

Working smarter, not harder: silencingLAZY1inPrunus domesticacauses outward, wandering branch orientations with commercial and ornamental applications.

“…Wandering branches, as in corkscrew willows and Young's weeping birch, are prized for adding winter interest to landscaping. Interestingly, this phenotype has not previously been reported for LAZY1 knockdowns, even in woody species such as apple 15 . However, this phenotype may not be limited to plum.…”

“…LAZY homolog mutants across plant clades have wider lateral organ angles [8][9][10][11][12][13][14][15] . They also exhibit slowed or absent gravitropic response, sometimes to the point that shoots grow prostrate on the ground-as in Oryza sativa (rice) 16 , Zea mays (maize) 11 , and the Arabidopsis thaliana (arabidopsis) lazy1,2,4 mutant 13 .…”

“…Consistent with this, overexpression of some LAZY homologs led to narrower branch and root angles and enhanced gravitropism [17][18][19] . LAZY homologs also are involved in responses to light quantity and quality, likely functioning to integrate light and gravity signaling during the establishment of the default lateral organ angle or "set-point angle" 15,20,21 .…”

Advancing tree genomics to future proof next generation orchard production

“…LAZY1 acts as a negative regulator of the polar auxin transport (PAT) to decrease the response to gravity, and loss-of-function mutations in rice promote a branching phenotype that is more spread apart (Li et al, 2007;Yoshihara and Iino, 2007). In apple (Malus domestica), the MdLAZY1A-W allele has a single nucleotide substitution that changes the amino acid from leucine to proline resulting in a dominant weeping phenotype (Dougherty et al, 2023). In contrast, an in-frame stop codon mutation in LAZY1 in silver birch (Betula pendula) leads to a recessive weeping phenotype (Salojärvi et al, 2017).…”